NOTE: The FL7040 & FL7060 probes requires an FI7000 for power and communication.
Well actually, yes. These new laser-powered E-Field probes from AR are so versatile; they do the work of multiple probes, with outstanding accuracy and linearity for your demanding field monitoring requirements. They contain an internal microprocessor that provides advanced control and communication functions while automatically correcting for measurement drift caused by ambient temperature variations.
Our newest laser probes are available in two models, which cover an exceptionally wide frequency range. Model FL7040 covers the 2 MHz – 40 GHz range while Model FL7060 covers the entire 2 MHz – 60 GHz range.So you don’t have to settle for what they have, but what you want. Being a laser probe you also have theconvenience of never having to replace or recharge batteries. In addition, AR provides the largest family of probes in the industry.
Like all AR products, our new probes are backed by the best and most comprehensive warranty along with the strongest support in the industry.
To learn more, visit www. ar-worldwide.com or call us at 215-723-8181.
Model FL70402 MHz – 40 GHz range
Model FL7060 2 MHz – 60 GHz range
rf/microwave instrumentationOther ar divisions: modular rf • receiver systems • ar europeUSA 215-723-8181. For an applications engineer, call 800-933-8181.In Europe, call ar United Kingdom 441-908-282766 • ar France 33-1-47-91-75-30 • emv GmbH 89-614-1710 • ar Benelux 31-172-423-000
2 interference technology emc test & design guide 2010
SPECIAL FEATUREPAGE 20
2011 EMC TEST LAb dIRECToRy
More than 300 EMC Test Laboratories, arranged by state, with details of services offered and contact phone numbers, are presented as a quick reference guide to EMC testing services.
08 TESTING & TEST EQUIPMENT
1.04m Rod, Antenna Factor and Received Level in MIL-STD 462/461E Compared to MIL-STD 461F Test Set Up .....................8DaviD a. Weston, eMC Consulting inC.
Effective EMC Troubleshooting with Handheld Probes ............14terry noe, beehive eleCtroniCs; uDoM vaniCh, paCifiCa international
Managing EMC Performance of a Product as it Ages .............. 36gert greMMen, Ce test; tiM haynes, seleX s&as; ralph MCDiarMiD; eD priCe, CubiC Defense appliCations; john WooDgate, jM WooDgate anD assoCiates
USB Interface on Laboratory Surge Generators ....................... 42jeffrey D. linD, CoMplianCe West usa
46 EMC dESIGN / FILTERS
Clocking Strategies for EMI Reduction ...................................... 46sassan tabatabaei, sitiMe Corporation
2010contents
8 18
CHANGING THE STANDARDS
CST of America®, Inc. | To request literature, call (508) 665 4400 | www.cst.com
Y Get equipped with leading edge EM technology.
CST’s tools enable you to characterize, design and
optimize electromagnetic devices all before going
into the lab or measurement chamber. This can help
save substantial costs especially for new or cutting
edge products, and also reduce design risk and
improve overall performance and profitability.
Involved in EMC/EMI analysis? You can read about
how CST technology is used for EMC/EMI analysis
at www.cst.com/emc. If you’re more interested in
microwave components or signal integrity analysis,
we’ve a wide range of worked application examples
live on our website at www.cst.com/apps.
The force is with youUnleash the power of CST STUDIO SUITE®,
the No 1 technology for electromagnetic simulation.
Now even more choice for EMC/EMI simulation. The
extensive range of tools integrated in CST STUDIO
SUITE enables numerous applications to be analyzed
without leaving the familiar CST design environment.
This complete technology approach enables
unprecedented simulation reliability and additional
security through cross verification.
Y Grab the latest in simulation technology. Choose
the accuracy and speed offered by CST STUDIO SUITE.
4 interference technology emc test & design guide 2010
departments
Editorial.............................6
Test Lab Directory .........20
Index of Advertisers .....88
InterferenceTechnology—The EMC Directory & Design Guide, The EMC Symposium Guide, and The EMC Test & Design Guide are distributed annually at no charge to qualified engineers and managers who are engaged in the application, selection, design, test, specification or procurement of electronic components, systems, materials, equipment, facilities or related fabrication services. To be placed on the subscriber list, complete the subscription qualification card or subscribe online at InterferenceTechnology.com.
ITEM PublIcaTIons endeavors to offer accurate information, but assumes no liability for errors or omissions in its technical articles. Furthermore, the opinions contained herein do not necessarily reflect those of the publisher.
ITEMTM, InterferenceTechnology™—The EMC Directory & Design GuideTM, and Interference Technology.comTM are trademarks of ITEM PublIcaTIons and may not be used without express permission. ITEM, InterferenceTechnology—The Annual EMC Guide, The EMC Symposium Guide, The EMC Test & Design Guide and InterferenceTechnology.com, are copyrighted publications of ITEM PublIcaTIons. contents may not be reproduced in any form without express permission.
contents2010contents
55 LIGHtnInG,transIents&esd
How Smaller Form Factors Exacerbate ESD Risks and How Foil Resistors Can Help ........................................................................... 55Yuval hernik, vishaY international inc.
60 teLeCOm
Understanding the Changes to FCC 5GHz Part 15.407 Regulations ....................................................................................... 60DaviD a. case, cisco sYstems
62 sHIeLdInG
Differential Transfer Impedance of Shielded Twisted Pairs .... 62michel marDiguian, emc consultant
74 pOWerQuaLIty
System Compatibility an Essential Ingredient for Achieving Electromagnetic Compatibility and Power Quality for Lighting Control Systems ...............................................................................74philip keebler, kermit phipps, Frank sharp, epri lighting laboratorY.
76
64
Validate your radiated and conducted test setup daily in less than 10 minutes.How many times has it happened? After completing a test or a series of tests, a problem is discov-ered which brings the results into question. It can be due to some malfunctioning instrument or a bad connector or cable? Use the Comb Generator as a reference signal source to quickly verify the OATS or Anechoic chamber. Com-Power Comb Generators are available up to 34 GHz. Please read the application note on our website www.com-power.com/tech-notes.html for more details.
OTHER PRODUCTS INCLUDE: Antennas • Spectrum Analyzers & Receivers • Near Field ProbesPreamplifiers • LISNs • CDNs • Power Amplifiers • Turntables • Masts & Tripods
114 Olinda Drive, Brea, CA 92823 • tel 714.528.8800 • fax 714.528.1992 • [email protected]
S u b s c r i p t i o n sITEM, InterferenceTechnology—The EMC Directory & Design Guide, The EMC Symposium Guide, The EMC Test & Design Guide and The Europe EMC Guide are distributed annually at no charge to engineers and managers who are engaged in the application, selection, design, test, specification or procurement of electronic components, systems, materials, equipment, facilities or related fabrication services. Subscriptions are available through interferencetechnology.com.
As the economy gained momentum in late 2009 and early 2010, engineering organizations, like every other business
sector, sensed promise that a strong, self-sustaining recovery was kicking in. Yet, as government spending to stimulate the economy trailed off and businesses concentrated on rebuilding their inventories, the growth rated started to slow – a pattern that continued through the summer.
Long-term economic growth rate - trending at about 2.5 percent - is not much better, but several market reports released by industry analyst NanoMarkets this year indicate that there are indeed some bright spots for the EMC community.
EMC materials and components markets had until recently been considered highly mature, with few opportunities for firms that were not well established in this field. However, the dramatic increase in the use of radio frequency emitters in the recent past has given a boost to the industry.
In addition to the most visible drivers for the EMC protection markets such as the rise of WiFi and 3G mobile communications, less obvious opportunities are appearing, including the spread of wireless-based navigation systems and electric and hybrid vehicles in the automotive industry, and EMI/RFI and electromagnetic pulse concerns in military electronics. (Smartphones generated 46% of traffic in May 2010, up from 22% two years ago, and 24% of traffic in the U.S. came over Wifi, according to mobile advertising marketplace AdMob. U.S. handset-based navigation usage rose to 24% in 2010 vs. 19% in 2009).
New business revenue opportunities for conductive coatings are emerging from developments in the display, lighting, solar panel, battery and sensor markets. The makers of conductive coatings also will have the opportunity to capitalize on the growth in e-paper and touch-screen displays and the resurgence of crystalline silicon photovoltaics.
Conductive polymers and nanomaterials are gaining importance in the EMI/RFI sector and there is a robust market for laminates and tapes, as well as higher value component products.
Finally, increased miniaturization of PCBs and hard drives coupled with ever smaller devices on computer chips will increase the threats of damage and costs caused by static electricity which will, in turn, provide the ESD products and coatings market with growth for years to come.
Thus, even as uncertainty remains pervasive throughout the global economy, EMI engineers can take heart in their industry’s resiliency.
8 interference technology emc test & design guide 2010
MIL-STD 462/461E CoMparED To MIL-STD461F TEST SET Uptesting & test equipment
david a. Westonemc consulting inc. merrickville, ontario, canada
i. introduction
This paper shows that the antenna factor of the receiving rod antenna and the E field incident on it, from a standard
source of radiation, both change when the counterpoise of the rod is either isolated from the ground plane on the table (new MIL-STD-461F set up), or connected, as per MIL-STD-461E and earlier.
The antenna factor (AF) in dB is defined as 20 log the incident E field in V/m divided by the received level in volts 20*log(E/V).
Reference 1 and Reference 2 discuss the measured antenna factor (AF) of the 41 inch (1.04m) receiving antenna with buffer. The measurements were made using different sources, such as a vertical transmission line and a second passive 1.04m monopole.
It was establ ished that both the inci-dent E field and the AF depends on the type of source and on the connection of the monopole coun-terpoise to ground. MIL-STD-462 and MIL-STD-461D and E show the counter-poise extended and connected to the table via a bonding strap. This strap is often a
metal sheet with the same width as the monopole counterpoise, as specified in MIL-STD-461E. One of the two configura-tions tested and reported in this paper was with a metal sheet bonding strap connecting the antenna counterpoise to a ground plane on the table top. MIL-STD-461F categori-cally states “For rod antenna measurements, electrical bonding of the counterpoise is prohibited” and this was the second con-figuration tested. This paper shows that measurements made with the counterpoise bonded versus not bonded results in very different received levels. MIL-STD-461F also modifies the rod antenna height so that the center point of the rod is 1.2m above the floor ground plane.
ii. MeasureMent set upIn all measurements the receiving rod
antenna cable was loaded with 28 material cores. This provides a high impedance and reduces common mode currents on the antenna cable.
The E field incident on the rod antenna, measured with the rod removed is made using a 10cm long bow tie antenna. This is connected to a low noise differential input buffer amplifier with an input resistance of 2 Megohms and an input capacitance of approximately 3pF. The wiring from bow tie to differential input adds approximately a further 2.2pF of capacitance. The differen-tial input is converted to a single sided signal and applied to a detector with a logarithmic response. The detector allows a very high dynamic range. The output of the detector is connected to an A/D converter the output of which is translated to a digital data stream which is the input of a fiber optic driver.
1.04m rod, antenna Factor and received Level in MiL-std 462/461e compared to
MiL-std 461F test set up
Figure 1. Photo of test set up.
CPI: Powering your world.
For more information please contact:Communications & Power Industries Canada,Inc.45 River Drive, Georgetown, Ontario,Canada L7G 2J4
For Sales offices worldwide please e-mail: [email protected] look us up on the Web at: www.cpii.com/emc
TWTAs for EMC applications
1.0 -18.0 GHz up to 1000 W CW (10 kW available over select bands)
18.0-40.0 GHz up to 150 W (2.0 kW over select bands)
40.0 – 50.0 GHz up to 80 W
Full Pulsed Amplifier Suites to 8 kW (megawatts pulsed power capability)
Meet the new automotive and military EMC standards with CPI high-powered TWT amplifiers.EMC facilities worldwide depend on CPI amplifiers for superior performance, reliability, and quality. CPI has a proven track record of consistent performance, service, and support. For EMC testing, CPI is the only manufacturer of both the TWT and the amplifier, ensuring quality designs and smooth operation. CW and pulsed amplifiers are available from 1 to 95 GHz, with power levels exceeding 2 kW over selected frequencies.
C
M
Y
CM
MY
CY
CMY
K
CPI_EMC_WORLD_1page.pdf 1 10/1/09 8:45 AM
10 interference technology emc test & design guide 2010
MIL-STD 462/461E CoMparED To MIL-STD461F TEST SET Uptesting & test equipment
The electronics and battery are contained in a 6cm x 6cm x 2.5cm shielded box and the only connection to the box is the non-conductive fiber optic cable. The 10cm bow tie is connected to the box using 13cm long thin wires. Thus the perturbation in the measured E field by the measuring antenna cable and equipment is kept to a minimum. The bow tie is calibrated under a strip line antenna. Reference 1 describes the test set up in more detail.
The source is a 0.44m x 0.38m metal box, representing the Equipment Under Test (EUT). The box is insulated from the ground plane and connected to the center conductor of an N type connector mounted in the table top ground plane. The front edge of the box is 10cm from the front edge of the table in a typical MIL-STD test set up. A photo of the test set up is shown in Figure 1. The signal is injected between the box and ground plane which simulates an EUT with an RF potential between the enclosure and ground plane. This potential is often the result of common mode currents on cables connected to the EUT. Even with the EUT enclosure bonded to the ground plane via a bonding strap, the RF potential may be developed when sufficient current flows to ground in the strap.
The measurements were made in a damped anechoic chamber to simulate a typical MIL-STDRE102 test. This chamber also contains localized ferrite tiles as well as absorber loads and is described in Reference 3 page 581. Although well damped above 50MHz the chamber does exhibit resonances below 50MHz. Reference 4 describes the chamber to chamber deviations for five different cham-bers. These range from one containing the MIL-STD-461F minimum absorber requirements to one containing hybrid absorber in a CISPR 25 compliant chamber.
III. MeasureMentsMany commercially available 1.04m rod antennas are
not calibrated but rely on a purely theoretical value based on antenna and buffer input capacitances. A test method useful from 0.01 to 5MHz, which simulates far field con-ditions using a plate antenna is described in Reference 1. The results using the plate antenna with a commercially available buffered rod antenna correspond well with the manufacturers published data. However when the source of radiation is a vertical transmission line, a second rod antenna or the enclosure in a MIL-STD-461 RE102 test set up the measured AF is very different from the far field and dependent on the source.
We measure both the E field incident on the rod antenna with and without bonding the counterpoise to the table as well as the AF of the rod antenna with and without counter-poise bonded. The most significant data for manufacturers of equipment is the received level with the same input signal level applied to the same source measured with and without bonding the counterpoise to the table. Here we assume that the manufacturer uses the same published far field AF of the rod antenna regardless of the test set up.
Figure 2 shows the AF measured both with and without the counterpoise bonded to the table. As seen in Reference 2 the variation in AF below 20MHz is much greater with the counterpoise not bonded. From 20MHz to 30MHz the AF with the counterpoise not bonded is 6dB higher and this is also seen in the Reference 1 test results. Reference 1 provides the AF calibrated on a free space range and the large variations seen in Figure 2 below 20MHz are missing indicating that these are due to the anechoic chamber.
The E field incident on the rod antenna is higher with the counterpoise bonded at most frequencies and this is shown in Figure 3.
Using the same buffered rod antenna the received level with the monopole counterpoise bonded is up to 18dB higher than with the counterpoise not bonded and this is shown in Figure 4.
Reference 4 describes a traditional (MIL-STD-461E) monopole antenna set up in five different chambers with different types and amounts of absorber. It also describes measurements made with a MIL-STD 461F set up. The source of radiation was either a vertical rod above the table top ground plane or a horizontal rod above the table top ground plane. From Reference 4 these resonances are at-tributable to “ RF current loops between the counterpoise, ground plane, ground plane to chamber connection point (wall to floor), chamber floor and the capacitive coupling back to the antenna counterpoise causes resonant condi-tions”. However, in Reference 2 the measurements with the counterpoises uncoupled on a free space range with no un-derlying ground plane shows exactly the same dip followed by peak in AF with approximately the same magnitude as References 4 and 5.
The power cords to the signal generator and spectrum analyzer in the Reference 2 measurement were the only connection to ground and the transmit rod and receive
Figure 2. Measured AF of monopole with and without counterpoise bonded and with a simulated EUT as the source.
Measurement with counterpoise bonded Measurement without counterpoise bonded
PARTNERSHIP FOR DEFENSE INNOVATION RESEARCH & DEVELOPMENT LABThe PDI R&D Lab is a 10,000 sq. ft. facility located in the All American Military Business Park in Fayetteville, N.C., next to Fort Bragg. The lab provides electromagnetic compatibility (EMC) testing, environmental testing, RF emissions pre-compliance testing, engineering design, integration, and consulting services to local, state, regional government and commercial clients.
ENGINEERING SERVICES • Feasibility Studies
• Design Engineering
• Network Engineering
• IT & Communications System Integration
• Field Testing
• Network Component Testing
• End User Security Training- Gov’t Only
• Network Connectivity • 100 Megabit per second Ethernet connection to the North Carolina Research and Engineering Network (NCREN) and peered networks such as the Internet2, National LambdaRail, and the Defense Research and Engineering Network (DREN).
EMC COMPLIANCE TESTING
The PDI R&D Lab performs EMI/EMC testing in a large shielded semi-anechoic test chamber which simulates an open field, radio frequency quiet environment.
• Shielded from outside environment
• Internally lined with RF absorbing materials
• Capable of testing small or large systems
• Cell phones, routers, wireless devices
• Vehicular-mounted systems
•Rack-mounted systems
SEMI-ANECHOIC EMI CHAMBER • Dimensions
36’L x 36’W x 18’H
• 24 ft. turntable capable of handling a 55,000 lb payload
The PDI R&D Lab performs environmental testing utilizing specialized environmental test chambers to include:
Vertical Air-to-Air Thermal Shock Chamber • Work Space Volume
9 Cubic feet (225 L)
• Temperature Range
-75˚C to +190˚C (Cold Chamber)
+70˚C to +210˚C (Hot Chamber)
• Temperature Stability
±1˚C after recovery period
• Dimensions
Product Test Area: 25”W x 25”D x 25”H
Temperature Humidity Chamber • Work Space Volume 32 cubic feet (905 L) • Temperature Range -73˚C to +190˚C • Humidity Range 10% to 98% RH • Interior Dimensions 38”W x 38”D x 38”H • Shelf Load Capacity • 100 lbs distributed • 55 lbs concentrated
Temperature Altitude Chamber • Work Space Volume 32 cubic feet (905 L) • Temperature Range -73˚C to +177˚C (Achievable from site level to 40,000 ft.)
Altitude without temperature control, 100,000 ft. • Temperature Control ±1˚C at site level • Interior Dimensions 38”W x 38”D x 38”H
12 interference technology emc test & design guide 2010
MIL-STD 462/461E CoMparED To MIL-STD461F TEST SET Uptesting & test equipment
rod cables were covered in 28 material ferrite. This means that some other mechanism may at least contribute to the dip and peak.
The measurements described in Reference 4 showed the resonance effects to be greater from 10MHz to 30MHz in the MIL-STD-461E set up compared to MIL-STD-461F whereas our measurements showed the reso-nances to be greater in the MIL-STD-461F set up. Reference 5 describes an analysis of the MIL-STD –461E and MIL-STD-461F using a bare room without absorber. Here the predic-tion is that the resonant frequencies change but the amplitudes remain the same when comparing MIL-STD 461E to F. The same paper shows the room resonances with only 10cm absorber foam but no resonances from 3MHz to 30MHz with 100cm foam exhibit-ing only 9.5dB attenuation at 30MHz.
Reference 4 shows the received level for a vertically oriented source in a well damped chamber to be from 5 to 8dB higher for MIL-STD-461F and 5-10dB higher for the horizontally oriented source.
Figure 3. Measured E field incident on the antenna counterpoise with the rod removed.
Whereas Reference 5 shows the theoretical received level to be 10dB higher for MIL-STD-46E versus MIL-STD-461F set up. Also Reference 2 shows the AF to be 21dB higher at 16MHz for the MIL-STD-461F set up i.e. 30dB (with delta in E field from Figure 4 ) – 8dB from Figure 2 = 21dB. This means that the received level may be 21dB lower for the MIL-STD-461F versus MIL_STD-46E test set up. The major difference in the Reference 2 set up was that the measurements were made on a free space range with and without ground planes under a trans-mitting rod antenna and a receiving rod antenna.
This report shows 18dB higher received level for the MIL-STD-461E set up.
Reference 2 also showed the re-ceived level from a vertical wire 10cm above a vertical ground plane was higher in the MIL-STD-461E versus MIL-STD-461F test set up. The verti-cal test set up simulated cables routed down a 18 inch rack. The vertical test set up simulated cables routed down a 18 inch rack.
Measurements with rod removed and without bonded counterpoise. 10cm bow tie
Measurements with rod removed with counterpoise bonded. 10cm bow tie
IV. ConClusIonsReferences 2, 5 and this report (above 20MHz) show the
output level from a 1.04m rod antenna to be higher with a MIL-STD-461E test set up than MIL-STD 461F. From this report and , depending on the source of radiation, we see it may be up to 18dB lower in the MIL-STD-461F test. This is important information for EMI test personnel and manufacturers of equipment as it means that an EUT which fails RE102 from 10kHz (2MHz) to 30MHz in earlier MIL-STD-461E (and lower) measurements may now pass using the MIL-STD-461F test set up.
reFerenCes• [1]. D. A. Weston Calibration of the 41 inch (1.04m) receiving mono-
pole. Available on the EMC Consulting web site http://www.emcco-nsulting.com/docs/1mMono.pdf, Feb 22 2009
• [2]. D. A. Weston. High frequency calibration of the 41 inch (1.04m) receiving monopole with and without connecting counterpoises and with different sources. EMC Europe. Wroclaw Poland Wed. 15/09/2010
• [3]. Electromagnetic Compatibility Principles and Applications: D. A. Weston, Marcel Dekker 2000
David A. Weston is principle EMC Engineer at EMC Consulting Inc., Merrickville, Ontario Canada. A member of IEEE and NARTE, Weston has worked full time in EMC for the last 30 years. He is author of the book “Electromagnetic Compatibility: Principles and Application,s” as well as numerous papers and reports, many of which are available at emcconsult inginc.com. He studied at Croydon Technical College from 1960 to 1965. n
Figure 4. Received level from the buffered monopole from the same source with and without the antenna counterpoise bonded to the table ground plane.
MORE ON OUR wEbsitE
Dealing with MIL-STD issues? The
Interference Technology website
includes a Testing Channel focused
on standards, test products and
developments and a Testing
Forum. Whatever the testing needs
of a particular application,
you will find many sources of
valuable information at
www.interferencetechnology.com.
STANDARD 5 YEAR WARRANTY ON ALL MACTON PRODUCTS!
EMI, RFI, EMC &RadaR TuRnTablEs
Custom Engineered Antenna and Radar Profiling Positioning Equipment
Indoor and outdoor applications•systems ranging up to 60’ in diameter•100–ton capacities•Variable speed control capabilities •and positioning accuracy of ±0.001°dozens of military and private •contractor installations
Measurement without counterpoise bonded Measurement with counterpoise bonded
14 interference technology emc test & design guide 2010
EffEct ivE EMc troublEshoot ing with handhEld ProbEs testing & test equipment
Terry NoeBeehive electronics sebastopol, cA
Udom VaNich Pacifica international rohnert Park, cA
iNTrodUcTioN
EMC testing is an unavoidable part of the development cycle for electronic products. As clock frequencies con-
tinue to increase, radiated emissions get harder to control. In an ideal world, the R&D engineer would test the emissions from his product early in the design stage and retest frequently as design changes were made, just ass he tests whether his product meets its other design requirements.
Unfortunately, practical constraints make this difficult. Regulatory requirements dictate that radiated emissions be tested at open sites or in shielded rooms. Most companies don’t have the equipment to do this testing, and subcontract it to outside test houses. Even if a company has its own test facilities, these may be booked well in advance, making testing difficult. Either way, the end result is that EMC testing fre-quently is not done until late in the project development cycle. As a result, designers do not discover EMC failures until late in the development cycle, when schedule pressures are at their highest.
The TesT-Tweak cycle When a product fails EMC testing, the
design engineer brings the product back to the lab and tries to isolate the source of the problem. Using measurements, rules of thumb, and intuition, he makes modifica-tions to the design. These changes might include adding shielding to problem cir-cuits, adding filtering to I/O lines, or other modifications.
The product is then returned to the EMC test site, and the tests are repeated. If the product fails, this cycle is repeated again, as many times as necessary:
Each iteration through the loop delays product shipment, costs money, and adds to frustration.
To break this loop, we need to be able to do two things: To make radiated emissions measurements on the bench, and to be able to establish correlation between measure-ments in the lab and measurements at the test site.
esTablishiNg lab-TesT siTe correlaTioN The lab engineer can measure emissions from his product in the R&D lab using handheld EMC probes. The ideal probes have the following characteristics: • Handheld • Repeatable • Compact • Flexible • Wide frequency response • Sensitive to magnetic or electric fields
The probes in the Beehive Electronics 101A EMC probe set have all these char-acteristics. Unlike homebrew probes, their sensitivity is known and specified. The
effective emc Troubleshooting with handheld Probes
With More Control And A More Intuitive Interface. AR’s new SW1007 software performs Radiated Susceptibility and Conducted Immunity tests automatically. So that’s one less thing you have to worry about. Actually, it’s a lot less things – including test accuracy and customized test reports.
New features include: • New user interface that’s easier to navigate • Improved report control • Tracking/notification of equipment calibration dates • More calibration options: • Ability to control more equipment The SW1007 comes with standards built in: • Updated test set-up screen IEC/EN, DO160, MIL-STD-461. GR1089, ISO/Automotive. You can change the test standards with just one click; and adding test standards is simple.
FREE Software Available Now! To request your free SW1007 EMC test software, complete the form at www.ar-worldwide.com/SW1007.Or ask your AR sales associate for a free hard copy. It’s easy to use. It’s accurate and it’s free. That’s a win/win/win. Unless, of course, you really enjoy spending all that time running tests manually.
To learn more, visit www.ar-worldwide.com or call us at 215-723-8181.
Fully Automated EMC TestingEasier & Better Than Ever.
rf/microwave instrumentationOther ar divisions: modular rf • receiver systems • ar europeUSA 215-723-8181. For an applications engineer, call 800-933-8181.In Europe, call ar United Kingdom 441-908-282766 • ar France 33-1-47-91-75-30 • emv GmbH 89-614-1710 • ar Benelux 31-172-423-000
16 interference technology emc test & design guide 2010
EffEct ivE EMc troublEshoot ing with handhEld ProbEs testing & test equipment
"The Test-Tweak Cycle” probe set con-tains both magnetic- and electric-field probes, with individual probes opti-mized for different frequency ranges. Since the probes use push-on SMB con-nectors, cables won’t kink when twist-ing the probes to reach tight corners.
With repeatable probes, it is pos-sible to establish correlation between measurements on the lab bench and measurements at the EMC test site. The lab bench and test site readings will then be related by a simple frequency-dependent offset. Although it is difficult to predict this offset in advance, it is easy to calculate it in practice with data from both locations.
aN examPle of sUccessfUl TroUbleshooTiNg The following example shows how these principles have been successfully used in practice to solve EMC problems by one of the authors.
The product in question underwent radiated emissions testing to CISPR 11 specifications. After testing in the semi-anechoic room (Figure 2), the device un-der test (DUT) failed the specification at a frequency of 100 MHz (Figure 3, 100 MHz peak marked with red arrow).
In the graph of Figure 3, the dashed red line represent the pass-fail limit for testing in this particular semi-anechoic room. The 100 MHz emissions were approximately 22 dB beyond the speci-fication limit. This was an alarming problem. Experience suggests that it is very difficult to improve emissions by over 20 dB without significant design changes.
A problem of this magnitude will usually require several design changes to improve the emissions enough to meet the specification. The typical ap-proach would be to make a number of design changes to improve the emis-sions. After each change, the DUT would be returned to the semi-anechoic room and radiated emissions testing would be repeated. This process is both time-consuming and expensive. In this case, the project schedule would not allow the weeks that might be required to solve the problem.
For this reason, it was necessary to take a different approach. Rather than Figure 1. The Test-Tweak Cycle.
If you are developing prototype electrical devices and need to evaluate the EMI performance of your new designs and devices, Agilent’s N6141A/W6141A EMC measurement application for its X-Series signal analyzers can help complete your compliance testing successfully. It is the only pre-compliance test solution that enables you to reduce test margins while ensuring your device meets all regulatory limits.
Reduce test margins with superior measurement accuracy• Identify low-level signals with excellent sensitivity from X-Series signal analyzers• Ensure more precise signal measurements
Easily identify out-of-limit device emissions• See device emissions typically hidden in the noise fl oor• Differentiate between ambient and DUT signals using signal list features• Identify intermittent signals using Strip Chart features
Maximize signals and compare against commercial and MIL-STD limits• Meet test requirements with built-in commercial and MIL-STD compliant bandwidths, detectors and presets• Compare measured emissions with pass/fail and delta indicators• Use frequency scan to identify, measure and store results
To learn more about EMI testing, request the free application note Making Radiated and Conducted Emissions Measurements at www.agilent.com/fi nd/emc-int
The concept of getting a new product to market on time and within budget is nothing new. Recently, manufacturers have realized that electromagnetic interference (EMI) compliance testing can be a costly bottle neck in the product development process. To help ensure successful EMI compliance testing, pre-compliance testing has become an important addition to the development cycle. The basic premise is to measure the conducted and radiated emissions performance of a product during the development phase to identify problems early and thereby solving them before moving on to the next phase of development.
Conducted and radiated EMI emissionsMany manufacturers use EMI measurement systems to perform conducted and radiated EMI emissions evaluation prior to sending their product to a test facility for full compliance testing. Conducted and radiated emissions testing focuses on unwanted signals that are on the AC mains generated by the equipment under test (EUT).
Pre-compliance testingThe frequency range for conducted commercial measurements is from 9 kHz to 30 MHz, depending upon the regulation. Radiated emissions testing looks for signals broadcast for the EUT through space. The frequency range for these measurements is between 30 MHz and 1 GHz and based upon the regulation, can go up to 6 GHz and higher. These higher test frequencies are based on the highest internal clock frequency of the EUT. This preliminary testing is called pre-compliance testing.
18 interference technology emc test & design guide 2010
EffEct ivE EMc troublEshoot ing with handhEld ProbEs testing & test equipment
The source was quickly identified as the DUT’s LAN cable.
Next, the DUT’s cov-er was then removed and further probing was done inside the box. Using the probe, it was easy to identify the source of the emissions. The 100 MHz emission was the 5th harmonic of the 20 MHz microprocessor clock in the system. This was cou-pling into the LAN circuitry and, from there, coupled onto the LAN cable.
With the source of the problem identified, the next step was to use the probe to evaluate the effectiveness of design changes. When ‘sniffing’ for radiated emis-sions, repeatability will be improved if the probe loca-tion is held constant. For
this reason, the probe was at-tached directly to the LAN cable with cable ties (Figure 4). The probe output was monitored on a spectrum analyzer.
The spectrum analyzer was tuned to a center frequency of 100 MHz, and the level of radiated emissions was read using the spectrum analyzer’s markers. Several changes to the design were made. After each design change, the level of the 100 MHz emission was recorded.
Three changes were identified that made significant improvements in the level of radiated emissions: • Ferrites were added to the transmit and receive lines
between the LAN transformer module and the RJ45 connector.
• The LAN transformer was changed to a model with a built-in EMI suppressor.
• The LAN cable that ships with the product was changed to one that had a ferrite core around it. Although this was effective, it raises difficult issues. Even if the product is shipped with the special LAN cable, there’s nothing to prevent the customer from using an ordinary cable in the field. Benchtop measurements predicted that the first two
modifications, taken together, would reduce emissions by the required 22 dB. The third fix, changing the LAN cable, should not be necessary. The DUT was returned to the semi-anechoic room with the first two changes, and the CISPR 11 test was repeated. The results are shown in Figure 5 (100 MHz peak marked with red arrow).
As can be seen from the graph, emissions at 100 MHz were reduced enough to meet the CISPR 11 specification. Despite the fact that over 20 dB improvement in 100 MHz emissions was needed, the first test of those improvements
evaluating each design change in the semi-anechoic room, each design change would be evaluated on the benchtop in the R&D lab using a small magnetic field loop probe. The improvement in radiated emissions would be measured for each design change. Only when lab measurements showed that the improvements were sufficient to enable the DUT to pass spec would the DUT be returned to the semi-anechoic room for additional (and hopefully final) testing. If the correlation between benchtop and test site measurements was good enough, only one more pass through the semi-anechoic room would be necessary.
Back in the lab, the first step was to identify the source of the emissions. A small magnetic field loop probe was used to find the location of the strongest 100 MHz emissions.
Figure 2. Radiated emissions testing in the semi-anechoic room.
resulted in success. Because radiated emissions could be measured effectively on the lab bench, the test-tweak cycle had been broken.
TERRY NOE has worked for 25 years in the fields of EMC, RF, and analog
design. He is president of Beehive Electronics, which produces a line of EMC test equipment. He also pro-vides consulting and custom design services in the fields of EMC, RF elec-tronics, and transceiver design. He received a BSEE from Virginia Tech in 1985 and a MSEE from Stanford University in 1989.
Udom Vanich received a bach-elor’s degree in Electrical Engineer-ing from San Jose State University and a master’s degree in Electrical Engineering from Colorado State University in 1987. He was co-founder of Pacifica International, LLC from 2003 to 2006. He is currently an RF application engineer for CSR. n
Figure 4. Lab measurement of radiated emissions.
Figure 5 (left). Radiated emissions after design changes.
MORE ON OUR wEbsitE
Handheld probes are just one solution to EMC troubleshooting.
Get information on the latest news and products on the
Testing Channel at www.interferencetechnology.com.
20 interference technology emc test & design guide 2010
ESD
Euro
CErTI
FICATI
oNS
FCC PA
rT 15
& 18
FCC PA
rT 68
IMMu
NITY
LIGHT
NING S
TrIKE
MIL-S
TD 18
8/12
5MI
L-STD
461/
462
NVLA
P/A2
LA AP
ProV
ED
ProD
uCT S
AFETY
rADH
AZ TE
STING
rS03
> 20
0 V/M
ETEr
rEPA
Ir/CA
LIBrA
TIoN
rTCA D
o-160
SHIEL
DING E
FFECT
IVENE
SS
TEMPES
T
BELLC
orE/
TELCo
rDIA
CB/C
AB/T
CBEM
ISSIoN
SEM
P/LIG
HTNIN
G EFFE
CTS
City Companyname ContaCt
2011 emc test lab directory
2011emCtestLaboratoryDirectoryCommonsenseteLLsus that most engineers and designers prefer to use local testing facilities. We have created an easy-to-use directory of labs and their services grouped alphabetically by state and city, so that our readers can identify those labs closest to them. We have endeavored to make this directory as accurate as possible; however, we realize that we have not found every lab or listed every service offered. If you own or work for an EMC test lab and we have missed you or omitted one of your services, please let us know. You can add a listing or update your current listing by logging onto www.interferencetechnology.com and following the easy step-by-step instructions. You can also e-mail your addi-tions, revisions, and suggestions to [email protected].
The listings above— Interference Technology’s “2011 EMC Test Lab Directory”—are our effort to provide our readers with accurate and current information on the vast number of testing capabilities available. We also realize that events move swiftly in the testing sector and that new services are added on a regular basis. If, after reading the Directory, you notice an inaccurate inclusion or omission, please join the effort for accuracy by forwarding the details to [email protected].
Interference Technology eNews brings you a weekly dose of:
• News• Standards Updates• New Product Announcements• Conferences and Events• Contract and Award Announcements• Surveys• Forums• Product and Services Directories• Jobs• White Papers and Application Notes
Get all this and more delivered directly to your inbox once a week.
Join the growing number of subscribers to stay up to date – subscribe online today.
Sign up today at www.interferencetechnology.com
Your weeklY eMC update!
EM TEST AG; Reinach, Switzerland; +41 61 717 91 91www.emtest.com
Save Time and Money by Shopping From A Single SourceCom-power offers a wide variety of products for compliance testing. We provide quick delivery, the best warranty in our industry, and very reasonable prices.
OTHER PRODUCTS INCLUDE: Spectrum Analyzers & Receivers • Power Amplifiers • Turntables • Masts & Tripods • Product Safety Accessories
114 Olinda Drive, Brea, California 92823 • tel 714.528.8800 • fax 714.528.1992 • [email protected]
36 interference technology emc test & design guide 2010
testing & test equipment EMC PErforManCE ovEr a L ifEt iME
gert gremmen, tim haynes, ralph mcdiarmid, ed price, john woodgate
EMC performance of a product is likely to vary with age as the physical charac-teristics change, e.g. caps dry out and
metal junctions oxidize, etc. Obviously, the product is designed with the intention of consistent compliance over the life of the product, but are there any requirements or guidance relating to preventing or control-ling this change in EMC performance over time?
This question posed recently on a prod-uct safety forum garnered some interesting responses from EMC and product safety experts. Interference Technology delved a little deeper and asked a panel of experts their thoughts on the topic:
Can environmental factors that jeop-ardize EMC over a product’s lifetime result in performance, reliability and even safety implications?
gremmen: Yes, but it will need a risk analysis in the design phase to identify the risks associated with aging. That risk analy-sis should include the whole spectrum of aging aspects, from components, to solder-ing techniques, contact properties related to oxidation, moisture, vibration, but also need to incorporate equipment properties that are not expected to “age”, such as software.
The analysis also needs to consider
emc performance of a product over its lifetime
changing properties that at first sight do not impact EMC properties, such as enclosures of which radiation patterns and resonance properties may change and have a bigger impact on EMI as initially assumed.
Ultimately, it is impossible to maintain EMC properties over a long time, and there-fore a definition of the lifetime of a piece of equipment is required. Very little work has been done on the calculation of lifetime for electronics in general, but a lot of data on failure rates is available, for example, in soldered contacts, and individual compo-nents. I have been involved in developing a simple method of creating a lifetime expectation based on collected statistical data for component lifetimes, but that does not include many relevant aspects, such as enclosure lifetime under miscellaneous (hards) conditions.
PrICe: In the military product area, most products don’t live long enough for aging to be as important as the (usually) very hostile physical environment. One further specific instance is damage to cable / backshell junc-tions due to abuse by users and/or vibration and shock.
Haynes: Expanding only slightly, corro-sion can reduce screening at interfaces of boxes, cables, connectors etc., gaskets can deteriorate, components can age and affect EMI performance.
Can lifetime reliability be better as-sured by simulating product aging
before EMC testing is done? How can lifetime EMC integrity be assured when equipment is still gener-ally tested only once?
Woodgate: It depends on how realistic the simulation is, given that no simulation can be wholly realistic.
[Lifetime EMC integrity can be assured] by careful selection of components, operating them well below their maximum stresses and careful overall design (e.g., assure continued integrity of seams in enclosures).
Haynes: Some requirements (possibly customer require-ments in defence/aerospace) need environmental testing (heat cycling / vibration) to be completed before EMC tests are undertaken. No “repairs” are allowed between environ-mental and EMC testing.
PrICe: In a Qualification test scenario, it is our practice to run the temp cycling, vibration, humidity types of tests before the system goes to EMC. True, some tests (high-G shock, blowing rain, transportation shock, high-G centri-fuge) are often done on a separate system.
gremmen: I am not aware of simulation software with a view on EMC related to aging. I think that in order to incorporate aging as a factor in EMC, we need to lend a ear
to environmental testing specialists, and start collecting events, and try to couple this to EMC properties. A knowl-edge base may be created that allows designers to identify potential risks.
mCdIarmId: In my brief experience in private industry (since 1983) I can recall only one legitimate complaint concerning radio interference from a product. It’s my ex-perience that EMC problems during operational service of a product designed and verified through type testing to comply with the applicable standards is a rare thing, even over its operational lifetime. It may be that most products functionally fail and are removed from service before they become an EMC nuisance.
Many companies control the configuration of their prod-ucts by keeping a list of EMC critical components, much like a list of safety critical components for use in UL and CSA compliance. If a component, like a power MOSFET, needs to change manufacturer, then all the specifications are carefully checked and an EMC retest (at least for emissions) may be performed before qualifying the alternate source. If a product complies with the applicable RF emission and immunity standards, it will likely never be a problem dur-ing its lifetime.
38 interference technology emc test & design guide 2010
testing & test equipment EMC PErforManCE ovEr a L ifEt iME
Are there any regulatory requirements to artificially age a product prior to EMC testing? If so, are the requirements industry specific?
Woodgate: Not for commercial products in Europe, as far as I am aware.
Direct controls of performance are not appropriate for safety-critical applications. Each product has its require-ments set by following a procedure, which is described in the multi-part standard IEC 61508.
Haynes: There may be some implicit requirements, such as in section 6 of the UK Health and Safety at Work Etc. Act 1974 - Duties Towards Articles Used At Work. There may be other such requirements in legislation (possibly in the Provision and Use of Work Equipment?). There may also be requirements in Joint Airworthiness Requirements (JARs) that require a ground-based “golden sample” aircraft to be exposed to more hours of simulated flying than the worst-case flight-cleared aircraft of the type. This is to identify fatigue failures in the ground-based model before they can happen in the flight-cleared aircraft.
PrICe: USA military procurements are controlled by a strict and extremely specific list of contractually obligating “Line Items”, so this is all defined by the contract.
gremmen: There are no such regulations I am aware of. At least there are no such for ordinary commercial and residential equipment, not even for high-end laboratory equipment.
Can a well-defined maintenance schedule help en-sure regular surveillance of components that will affect the EMC performance of a product?
Woodgate: Possibly: Some EMC characteristics can be checked simply enough for inclusion in a maintenance schedule (e.g. low-frequency conducted emissions), while others cannot (e.g. high-frequency immunity). Some might think that ESD immunity could be checked in a mainte-nance process, but this raises safety issues in itself.
Haynes: Yes - but only where there is a conscientious maintainer. This may be much more important in respect of vehicle maintenance (screening of the engine management unit, braking control, etc.), than it would be to have annual maintenance on your TV or washing machine. However, how many garage mechanics would be trained in “EMC”?
PrICe: Military systems have several levels of mainte-nance, with the first line generally not going beyond “pull that box that doesn’t work and put in a new one.” First level people are usually not opening boxes, fixing cables or doing other intrusive things. At the depot level, a manufacturer should specify if EMC items should be replaced as part of maintenance (perhaps a particular EMI gasket is good for only a few open/close cycles).
GErt GrEmmEn is a senior test engineer in EMC and product safety for electronic and electrical products, director of ce-test qualified testing bv in the Netherlands and an expert in CE marking.
ralph mcDiarmiD, aSct, has 12 years ex-perience in power electronics circuit design and simulation - converers and inverters to 3kW - and 10 years experience with regula-tory international product approvals, includ-ing CSA, UL and CE.
ED pricE, a NARTE certified EMC engineer, has worked in the Electromagnetic Compat-ibility Lab at Cubic Defense Applications in San Diego, Calif. since 1993.
John WooDGatE of J.M. Woodgate and Associates has a background in the consumer products and sound reinforcement sectors of the electronics industry, as well as product management and marketing of audio, high fidelity and video products. He became an independent consultant in 1984.
* Participants’ comments do not necessarily reflect the views of their employers.
tim haynES, electromagnetic engineering specialist at SELEX S&AS, has worked on space systems, avionics, marine and sub-marine equipment for the defense industry and has employed forensic techniques in resolving problems, in particular EMC issues during design and development of hardware.
gremmen: Applications that require tight control of EMC properties during a defined lifetime definitely need adequate service. Maintenance has traditionally been focused on functional parameters only, even in aerospace and aviation technology. Many EMC-related components can get defective without even being noticed in functional testing, so additional testing has to be defined in order to recognize potential failures of this kind. While emission
gremmen: Many EMC properties of equipment are undefined in the design phase. If a problem during initial testing is found, remedial measures such as filters may help controlling emissions. However, the source of the problems is not under control. A change of manufacturer for a mi-croprocessor, for example, may change emission levels to a high degree, even if the component is pin and specification compatible. The EMC properties of such a component are in general not specified in a datasheet. A newer process on chip level, or even change of location of manufacture may impact those properties. The manufacturer is not bound to notice their customers, as EMC properties go undocu-mented. I lately witness a large number of SMPS related problems in EMI where just the ongoing progress in FET developments results in much faster switching times as before, creating substantial interference problems in the 30-200 MHz range. The manufacturers of the switchers, confronted with the problem, told us that they had updated their switching FETS as older (tested) models quickly became obsolete and the FET manufacturer provided them with equivalents and pin compatible models with a faster switching time. Even software can have an impact on EMC; simple changes in firmware (updates) can create sudden changes in emissions or immunity behavior that are completely outside the view of the software designers.
properties may be quickly established using, for example, a tabletop spectrum analyzer on a comparative basis (com-pared to a new piece of equipment), immunity problems will remain unnoticed until a full test suite for immunity has been carried out. As many EMC components have a function towards common mode phenomena, traditional test techniques that use differential mode signals are not capable of detecting failures in such components. A surge suppressor, for example, may be connected to the enclosure and not to system signal ground, and may look connected to nothing from the point of view of traditional automated test sets. In addition to that, commercial test setups for components operate on PCB level, and not on equipment or even system level.
Even with regulatory and contractual compliance established at the outset, could changes be made to a product that may compromise its EMC per-formance?
Woodgate: If you mean ‘changes during life’, the answer must be ‘yes’. [This can be avoided by] total encapsulation, making the product unrepairable. But then how can the heat be dissipated? Heat pipes? Such ‘heroic’ measures are hardly justified.
The largest range of impulse test equipment up to 100kV and 100kA A Swiss Company [email protected] www.emc-partner.com
40 interference technology emc test & design guide 2010
testing & test equipment EMC PErforManCE ovEr a L ifEt iME
Woodgate: It’s far too LATE at the onset of testing. These requirements must be applied at the outset of DE-SIGN, where they pay a dividend of around 1000%.
Haynes: There is much greater benefit to be obtained by considering ALL environment and EMC requirements that will apply during the product lifecycle at the very beginning - at the concept stage of the product/project.
PrICe: I think everybody says it’s good to plan ahead.
gremmen: Yes, if EMC is recognized to have a substan-tial impact on reliability and safety, taking in consideration all these aspects will create benefits for both manufacturers as well as consumers.
Do you have any anecdotal examples that illustrate the above points or would be helpful to fellow engineers?
Haynes: Some radio equipment was EMC tested af-ter vibration and thermal testing had been successfully completed. The equipment failed EMC on emissions and immunity. The cause was “cracked” semi-rigid coax / con-nector joints where either vibration or thermal expansion had caused the connector to cable-sheath interface to crack, causing the transfer impedance to increase and allow signals into / out of the coax cable. If the equipment had not been vibration / thermal tested before the EMC - this failure would not have been found.
PrICe: Same scenario; this time finding connector nuts that were improperly torqued and allowed the connectors to loosen. n
Given the fact that modern software development heavily depends on external modules and libraries, such changes may even be unnoticed to the manufacturer of the product. Again, EMC properties of the building blocks of electronic are most of the time undocumented.
And yes, during testing it is too late. Too many definite choices have been made at that point already.
Haynes: A rack of equipment installed in an EMC cabinet passes the required tests with the doors closed. The customer can use the equipment with the doors closed but they are always open because he wants to see the flashing lights and alpha/numeric displays to ensure the equipment is working ...
To limit customer-based changes - design products that are actually fit-for-purpose - or should that be fit-for-the-users-purpose. Otherwise implement measures to prevent EMC features being “overridden”.
PrICe: Keep close to your customer so they can acciden-tally show you all the new and exciting things they do with your product. You will learn the most interesting things.
Is there a benefit to considering environmental and EMC requirements at the outset of testing a product?
www.interferencetechnology.eu
The online edition of the 2011 Interference Technology Europe EMC Guide will be updated periodically during 2010/2011.
Subscribe online to receive notification of these edition updates.
42 interference technology emc test & design guide 2010
USB Interface on LaBoratory SUrge generatorStesting & test equipment
Jeffrey D. LinDcompliance West, usA del mar, cA
A s any laboratory engineer knows, harsh, noisy lab environments of-ten result in data loss and/or resets
of test equipment or host computers. A potential solution to this challenge is the successful implementation of mains power distribution in the lab, and an isolated se-rial/USB design for laboratory computer systems. This will allow the lab to utilize the strengths of both the computer’s USB interface and the laboratory equipment's existing serial interface technology.
The advent of USB controlled devices in the laboratory has been a boon in many ways. “Plug and play” devices make installa-tion easy, and ubiquitous USB connectivity on modern laptops and desktop comput-ers allow powerful data processing to be available easily. The speed of modern USB connections, USB 2.0 and above, allow real-time data collection. The hot-swappable feature allows technicians to change setups at will without worrying about restarting the computer.
USB connectivity does not always need to be used for real-time data collection. The convenience lends itself to other uses as well. For simpler installations, the inter-face between the test equipment and the personal computer is used only for control of the test equipment, to provide test equip-ment status for display on the computer
screen for operator convenience, or for basic housekeeping information, in which the computer is updated by the test equipment regarding its actions. In this case, the speed advantages of the USB interface are not realized, but the convenience of connection still makes the USB interface a good choice.
In many cases, operators who are rushed for time may not investigate a non-USB connection because these non-swappable interfaces require research or reboot, taking valuable time. If an operator is presented with the USB interface, which is a known commodity, he may be more willing to plug it in and enjoy the conveniences that were written into the interface.
In addition, the serial ports on comput-ers are no longer standard. In most cases, the serial and parallel ports which used to be supplied have been deleted in favor of more USB ports to connect to keyboards, printers, monitors, thumb drives and most everything else. So, in addition to the con-veniences of the USB interface, there is a practical requirement to use USB connec-tions because other connection protocols are simply disappearing from personal computers.
With this set of features and convenienc-es, as well as the issue regarding disappear-ing alternatives, the USB interface should be making RS-232 and GPIB installations obsolete. However, this is not the case at many laboratories and these older installa-tions are still the norm.
Table 1. Overview of interface protocols used in laboratory environments.
ing laboratory interface protocols all suffer from disadvantages which af-fect their usefulness in a laboratory environment. USB can offer distinct advantages but is not robust. The USB reset can exhibit loss of communica-tion between the test equipment and the computer, or in some cases a reboot of the personal computer connected to it. These conditions would preclude the USB interface from consideration in a laboratory environment, if the advan-tages were not so great. The usefulness of the USB interface certainly merits work toward making the interface more robust, so it can be used with interference-causing equipment such as surge generators, hipot testers and other similar equipment.
DeSiGn ConSiDerationS Serial interfaces use positive and
negative voltages for data transmission, so the effects of changes in ground potential are negated. This is a larger problem for USB, because the data
Automotive + Telecom + Consumer Products + Military + Industrial + Medical + Avionics
THE BEST EMC-TEST-EQUIPMENT FOR ANY APPLICATION:
EM TEST USA Inc. | Michael Hopkins | 3 Northern Blvd. Unit A-4 | Amherst, NH 03031Telephone: +1 603 769 3477 | Mobile: +1 603 765 3736 | e-mail: sales @ emtest.com www.emtest.com
Need more information?
Your direct line to EM TEST USA is + 1 603 769 3477
Interface Advantages Disadvantages
RS-232 • More noise-resistant
• 115 kbs max speed• Serial interface not
available on many personal computers
Parallel • User Familiarity
• 115 kbs max speed• Setup difficult• Parallel interface ports
44 interference technology emc test & design guide 2010
USB Interface on LaBoratory SUrge generatorStesting & test equipment
shifting ground voltage had little ef-fect on RS-232 communications. RS-232 did not have any error checking protocols but because of the robust hardware solution, it was not needed to make reliable connections. However, even with this robust signal communi-cation, a shielded cable was required, as external noise could overpower the RS-232 communication. Clearly, a more sophisticated protocol with er-ror checking was going to be needed
transmission uses a positive voltage and ground only. Therefore, noise and ground potential changes have a great-er effect, and this is the reason that USB interfaces have to be more carefully implemented for a good result.
In the days of RS-232 interface communications, there was 6 volts minimum swing between binary zero (-3V maximum) and binary one (+3V minimum). Since the voltage has to swing through ground potential, a
as noise in the laboratory increased. USB communication has many
protocols, and many incorporate er-ror checking, which should have been a boon to communication in noisy environments such as laboratories. Unfortunately, USB communica-tion design presents challenges for interface designers and users. Since the difference between a binary zero (+0.3 V maximum) and binary 1 (+2.8V minimum) is only 2.5V, and the because the zero is approximately ground referenced, the USB interface is more susceptible to disconnects and resets, which could result in a complete hardware collapse, where communication between the test equipment and the computer is totally lost. This will result in loss of control of the tester, and loss of data across the link. In general, the designer of the USB interface of the equipment must select a protocol that will detect a disconnect, reconnect the interface, and make sure the USB connection was recovered. Further, its design must include optical interface(s) to prevent varying voltage levels from causing data loss. Some interfaces use a dedicated microprocessor in order to allow even more isolation between the computer and the test equipment.
GroUnDinG of teSt eqUipment anD CompUterS
Even the most isolated design will still have to deal with the equipment grounding conductor, or ground lead. In the case of a powerful surge genera-tor, the ground plane can be displaced by as much as a few volts, which could cause interface disconnection and data loss. This happens because the surge tester can deliver thousands of amps in a few microseconds and this energy needs to be dissipated to the building ground. Any high resistance connections within the test setup or in the building grounding system itself can cause a rise in potential of the grounding lead for a short time while the energy is dissipated.
To combat this problem, it is necessary to make sure the building grounding system and the test setup ground leads are all in working order
Figure 3. Improper mains connection method. The surge tester and the computer share a grounding path. If the ground voltage rises due to the surge tester output, the USB connection may suffer a reset, and the computer could be damaged.
Figure 2. The proper method of connecting mains power to a computer-controlled surge tester. The surge tester and the computer are provided with individual paths to ground.
and firmly connected together. This step will solve many data loss and reset problems between computers and gen-eral test equipment, but in the case of surge test equipment, we recommend separation of the power lines (mains) of the computer and the test equipment, as shown in Figure 2. This step allows the ground current to flow separately from the test equipment to building ground, and not influence the ground potential of the computer. A separate ground for the test equipment will solve most USB reset problems. In order to clearly illustrate the point, Figure 3 presents an incorrect mains implementation, which has a greater chance of causing resets in the USB interface.
USB-Serial interfaceSIn many cases, it is not possible to
run separate mains circuits to labora-tory test equipment to prevent resets of the USB interface. There is another method which has solved problems, and that is to employ a hybrid inter-face, consisting of a RS-232 serial interface on the test equipment with a proprietary circuit which changes the protocol from RS-232 to USB before presented to the computer. This allows all the benefits of the USB interface to be used by the personal computer, and also allows the robust RS-232 interface to be used on the test equipment.
Location of the protocol change is important. Because of the strength of the RS-232 communication, the change to USB should be done as close to the computer end of the cable as possible. In addition, optoisolation of the interface change is impera-tive. This unfortunately leaves most commercial solutions out of consid-eration, as their unisolated interface changer is located at the RS-232 end of the cable.
SolUtion recommendationS
We have found that to be abso-lutely sure the USB interface will be robust, it is necessary to implement separate mains voltage sources for the test equipment, away from the
mains voltage of the computer, in ac-cordance with Figure 2 of this article, NOT Figure 3. In addition, an isolated hybrid interface consisting of RS-232 protocol at the test equipment end and USB protocol at the computer end should also be employed. The isolated interface should be located as close to the computer end of the cable as possible.
The Electronics Test Centre brings compliance, certification services,
customized test and engineering to the Automotive, Medical, Military,
JEFFREY D. LIND, president of Compliance West, USA, has 33 years of extensive electrical engineering expertise. Lind launched his career in the electrical product safety industry working at Underwriters Laboratories (UL) from 1976-1982, doing project engineering and follow up services management. He then lent his skills to Atari™ as a product safety engineer for a year. Shortly after moving to San Diego in 1983 to work with Sega Gremlin™, Lind decided to branch out on his own and launched Compliance West. n
46 interference technology emc test & design guide 2010
emc design / filters CloCk ing Strateg ieS for eMi reduCt ion
SASSAN TABATABAEIsitime corporation sunnyvale, cA
I. INTRODUCTION
Electronic devices have to operate in close proximity, whether it is in the home, office, industrial establishment,
or outdoors. Each of the devices may radiate electromagnetic energy, which can interfere with the operation of the rest of the devices. To avoid such harmful interference, govern-ments and industry bodies limit the amount of energy that any device can radiate. Envi-ronmental compliance standards such as FCC Class A and B specify these limits for different categories of equipment, based on the location of end use.
One of the key sources of electromag-netic interference (EMI) energy is the clock tree. Good design and layout of the clock tree ensures that the system not only performs well without major timing issues, but also ensures the system passes environ-mental compliance standards. Careful con-sideration must be given to the following: • The clock source and associated traces • The circuits that are the driven with
the clock. These circuits may consist of a number of discrete devices, but more often than not, it includes a small num-ber of large integrated circuits (ICs) that perform most of the key functions for that application.
• The I/O circuitry and traces that ex-change data from one IC to another or to external systems. Each trace (clock or data) can be con-
sidered a transmission line and different kinds of traces have varying characteristics.
Transmission line theory is well-established in the electronics industry, so we will not go into that detail in this paper.
The main reason for EMI radiation is lack of signal return path in transmission lines. This typically occurs when there is a discontinuity in the ground or signal return plane underneath the clock and signal traces. The EMI energy is typically concentrated at the clock frequency and its harmonics. The energy at higher harmonics depends on the clock signal shape. Because most clock signals have near square-wave shape with finite slew rate, the harmonics of the signal do play an important role in EMI. Generally, faster slew rates and overshoots/undershoots due to inadequate termination result in larger EMI at the frequencies of the harmonics.
The main EMI reduction techniques are as follows:
1. Shielding 2. Using solid ground or signal return path
for high-speed signals 3. Signal filtering 4. Reducing rise/fall time 5. Using spread-spectrum clocking (SSC) modulation
Shielding requires enclosing the system in a grounded conductive box to block the radiation of energy to the outside. In many consumer and computing applications, such enclosures are costly or are impractical due to the physical constraint of the system. The use of a solid ground is a recommended de-sign practice for not only reducing EMI, but also for maintaining good signal integrity in high-speed signal paths. However, small amounts of energy will radiate even in the presence of a solid ground from the top side of the trace. In some high density boards,
Clocking Strategies for EMI Reduction
Components
AssembliesComplex
At the NEW Spectrum Advanced Specialty Products, we've expandedour product capability to include a wider range of sophisticated components and assemblies. Our engineering teams continue to provide custom application-specific solutions exceeding our customer's mechanical, electrical and power requirements. TheSpectrum design process begins with our extensive library of standard components, which we frequently develop into custom assemblies offering you a more complete, high performance solution... saving you time and money.
Put our innovative new products & problem-solving expertise to work for you... visit our website or call 888.267.1195.
We cover the spectrum
Check out
the New Spectrum @
SpecEMC.co
m
Comp2Assemblies_InterTech:Layout 6 6/3/09 12:01 AM Page 1
48 interference technology emc test & design guide 2010
emc design / filters CloCk ing Strateg ieS for eMi reduCt ion
it may be difficult to guarantee a solid ground or return path for all signals without adding extra ground layers, which increases the board cost.
The following sections discuss the remaining three techniques in greater detail.
II. SIGNAL FILTERING FOR EMI REDUCTION
EMI may radiate from the signal output pins and traces. Typically, much of such radiation is from the board traces because the board traces are longer than the clock device pins or internal IC traces. In some cases, the short traces in the large IC pack-ages can dominate the EMI at rela-tively high frequencies (greater than 500 MHz).
Using low pass filters at the high-speed clock and data outputs effec-tively attenuates the signal frequency content, especially at high harmonics. Typically, simple RC-based low pass filters are used due to their simplic-ity, low cost, and small board space requirement. A RC filter is a single pole filter with 3dB attenuation at its cutoff frequency and 20dB/dec attenuation for frequencies above that. The cutoff frequency has to be approximately twice that of the clock frequency to avoid reducing the signal swing too much; otherwise the signal swing may violate the logic threshold of the receiver digital circuits. This filter is
suitable for reducing EMI at high har-monics; for example, it provides 20dB attenuation at the 11th harmonic of a clock signal. It is possible to design more complex filters, such as second order ones to attenuate higher har-monics even more, but they are more bulky and expensive.
Filtering technique has the follow-ing disadvantages: 1. The board designer has to place the
filters at the dominant EMI signal outputs, but it is often difficult to identify those signals. In designs where one clock source is driving one or two main ICs, placing the filter on the clock signal may be ef-fective solutions.
2. Low pass filters do not offer much EMI reduction at the main clock frequency and first two or three harmonics.
3. The filters present resistive and ca-pacitive load to the output drivers, which in turn increase the power consumption. The resistive current can be estimated by dividing the signal DC level by the equivalent resistor at the output. The capacitive current is computed as CVF, where C is the equivalent capacitance at the output, V is the voltage swing, and F is the clock frequency.
4. The RC filters take board space and increase the cost. This is especially true if separate filters have to be used for multiple signals traces.
Figure 1. Clock signal harmonic amplitude decreases as the rise/fall time increases. Rise times are normalized to the clock period.
III. EMI REDUCTION THROUGH RISE/FALL TIME CONTROL
Reducing rise/fall time for single-ended clocks and signals is an effec-tive way of reducing harmonic EMI. Figure 1 shows the amplitude of clock harmonics as a function of rise/fall time (rise and fall times are assumed to be the same). All the rise times are selected to maintain the peak-to-peak clock signal to its maximum value. As this figure shows, most harmon-ics can be reduced by 20dB or greater while maintaining the peak-to-peak clock swing. As such, the rise/fall time reduction provides better harmonic EMI reduction than RC filters without sacrificing the voltage swing.
Most single-ended drivers, such as LVCMOS, consist of push-pull circuits. In such circuits, the maximum drive capability of the driver and the effec-tive load capacitance define the rise/fall time. Therefore, there are two ways to increase the rise/fall time: • Increase the load capacitance. This
method has the disadvantage of increasing current consumption.
• Decrease the output current drive. This method does not increase the current consumption, but re-quires the clock device output drive strength to be programmable. Some clock devices and output buffers in the large ICs allow drive strength adjustment. Examples include programmable oscillators.
The main disadvantages of this EMI reduction method are: • It only reduces clock harmonic
EMI, and • It may not be possible to reduce the
rise/fall time sufficiently for high-speed clocks and signals.
IV. EMI REDUCTION USING SPREAD-SPECTRUM CLOCKING (SSC)
Waveform shaping methods, such as filtering and rise/fall control are ineffective for reducing the EMI gen-erated at the main harmonic from the clock traces. Additionally, they do not decrease EMI from the chipsets and traces that are driven by buffers with-out filters or rise/fall time adjustment. In addition to the clock traces, the data
lines may also radiate energy. Such energy is attenuated by the random nature of the data signals, but it may still exceed acceptable levels because there are typically many more data signals in a system than clock ones.
Board designers use slew rate control and proper transmission line design to reduce EMI, but due to large number of sources, the residual EMI at main frequency and its harmonics may still be high. In such cases, spread spectrum clocking is an effective system-wide EMI reduc-tion solution.
SSC is implemented by modulating the clock signal with a low rate frequency modulation. The modulation spreads the clock energy over a larger bandwidth, which reduces the maximum power for a given spectral bandwidth. The most common spectral bandwidth for measuring the peak EMI is 100 kHz, as defined by the federal communication commission (FCC). The SSC modulation rate in most ap-plications is 32 kHz to provide fairly flat response in the region over which the carrier frequency is spread.
The most commonly used modulation profiles is the triangular one, as shown in Figure 2b. This profile effec-tively distributes the carrier frequency energy uniformly over the modulation range and provides a fairly flat spec-trum at the clock frequency and its harmonics. Sinusoidal modulation does not provide the same flatness due to its non-uniform frequency distribution. Figure 2c shows Hershey-Kiss shaped modulation profile, which offers optimally flat carrier spectrum. This profile offers 1.5dB less peak EMI than triangular modulation, but it is more complex to implement.
Assuming that the clock frequency is modulated by a given percentage, SSCpercentage, and that the percentage harmonic spectrum is fairly flat after SSC nodulation, the peak energy reduction can be approximated as below:
where, ASSC(i) is the amplitude of the clock i-th harmonic amplitude after SSC modulation, fSSC _range is the frequency
range that the clock harmonic spreads over after SSC modulation, Aclk (i) is the clock i-th harmonic amplitude before SSC modulation, and RBW is the bandwidth for measuring EMI energy. The fSSC _range is computed as fSSC _
range = fclk (i).SSCpercentage. Therefore, the EMI reduction at the i-th harmonic can be com-
puted as below: ASSC(i)(dB) = Aclk(i)(dB) −10log10(SSCpercentage. fclk(i)/ RBW ) This equation indicates that the larger the clock fre-
quency, the larger the EMI reduction. Also, the EMI at the higher harmonics of the clock are reduced more than the lower ones.
The SSC modulation profile can be centered on the non-SSC clock frequency, or be less than the non-SSC clock frequency. The former is called center-spread, and the latter down-spread. The down-spread ensures that the SSC modulation does not cause periods shorter than those
SINE wave output filters
U
I
U
I
A) B)
U
I
U
I
A) B)
U U
I I
EMC
You don’t have to know everything about sinusoidal filters to select the best solution for your motor drive system. That’s our job. Why not go straight to Schurter for filters that improve system performance, reliability and efficiency?
Featuring our new FMAC SINE and FMAC SINE DCL filters designed to output clean sine waves from voltage wave forms produced by your system’s PWM frequency converter:
- operating voltage: 3x500/288 VAC- rated currents: 4, 8, 12 & 16A- motor power: 1.5 – 7.5 kW- motor frequency: 0-200 Hz- switching frequency: 2-20 kHz- FMAC SINE for cable length <=200 m; FMAC SINE with DC Link for cable length <=1000 m- screw-on mounting; screw clamp terminals
www.schurterinc.com/new_emc
- - - >
50 interference technology emc test & design guide 2010
emc design / filters CloCk ing Strateg ieS for eMi reduCt ion
of the clock without the SSC modula-tion. This is especially important for processor applications to ensure that that clock period does not violate the critical path timing in the internal state machines of the processor. The
down-spread, however, leads to an average frequency that can vary over a large range, e.g., a few hundred parts per million (ppm). Such large average frequency variation may result in buf-fer overflow in some I/O systems.
From design, quick-turn protos, and worldwide ISO9001 manufacturing, we are the superlative EMI solutions provider. The cornerstones of our mission are simple: Quality. Integrity. Service. Value. It is this commitment to total solutions without compromise that has led to our established position as a premier designer, manufacturer & distributor of EMI filters and magnetic products.
Plug into our comprehensive solutions. Radius Power is a leader in the design & manufacture of power products used to condition, regulate and govern electronic performance. The company provides a broad line of EMI Filters, Power Entry Modules, Power Transformers & Inductors to meet front-end requirements for AC & DC power line applications. We offer free pre-compliance testing for conducted emissions at our labs or yours! Bring us your EMI challenge & we will provide an optimized solution usually within 48 hours. Call Radius today.
Comprehensive EMI Solutions, On Time & On Budget
714-289-0055 PH 714-289-2149 FAX 1751 N. BATAVIA ST. ORANGE, CA 92865
www.radiuspower.com
The center-spread guarantees more accurate average frequency, but leads to short periods. For center-spread modulation, the user has to ensure that the processor and state machines are rated for the maximum frequency of the clock with SSC. The advantage is easier buffer management in the I/O systems.
Figure 3 and Figure 4 show the EMI reduction for the measured main harmonic of 12 MHz and 125 MHz clocks, respectively. The modulation range is 2% and modulation profile is triangular in both cases. These figures clearly show that the higher the clock frequency, the larger the EMI reduc-tion. Figure 5 and Figure 6 show the EMI reduction for the first, third, fifth, and seventh harmonics of a 100 MHz clocks with 2% down-spread triangular modulation. They indicate that the EMI at higher harmonics are reduced more than that of lower harmonics.
In our ISO 9001:2000-certificated factory, FILTEMC design and manufacture emi/emc filter for consumer goods, automation, telecom and machinery
etc in China. Most products have UL/CUL and CE certifications and comply with the RoHS Directive.
Please contact us for a catalog, or inquire your OEM/ODM needs.
Product range:
RoHS
SSC is used widely in certain ap-plications, such as printers and micro-controller applications because it offers the following advantages: 1. Reduced cost:
a. No need to use expensive shielding techniques. b. Recued ground layers. It may be
difficult to ensure that all data and clock signals have uninter-rupted ground plane underneath, which lead to EMI radiation from some traces. One solution is to add ground plane layers, but that adds board cost. SSC technique can reduce EMI and save addi-tional ground planes.
2. Flexibility: A system may be de-signed with non-SSC clocks. If the EMI testing shows EMI issues, the oscillator can be replaced with SSC ones to reduce EMI without chang-ing anything else in the system. Also, the SSC percentage may be adjusted to the minimum needed to meet EMI goals. This will minimize
Figure 3. Main harmonic spectrum for a 12 MHz clock with and without 2% down-spread triangular SSC modulation.
the impact on the system timing margins.
3. System-wide EMI reduction. Other EMI reduction approaches, such as
filtering, waveform shaping, ground plane continuity, and shielding reduce EMI at the specific places where this techniques are used. In
52 interference technology emc test & design guide 2010
emc design / filters CloCk ing Strateg ieS for eMi reduCt ion
contrast, adding SSC to the clock, reduces EMI from all signals that are synchronous with that clock regard-less of their locations. SSC modulation, however, is not
always a solution to EMI problems in the following situations: 1. SSC modulation increases period
jitter. For example, in 100MHz clock with 1% SSC modulation, the peak-to-peak period jitter increase by 1% of the clock period, or 100ps. When center-spread is used, some periods are shorter than the ones without SSC, which may violate the critical path timing in digital circuits. To avoid this issue, down-spread is of-ten the preferred SSC type because it guarantees that no clock period becomes shorter than the ones with-out SSC.
2. Deeper I/O buffers and more com-plex buffer management required. Many systems use two different clocks at the data source, e.g., a processor, and data sink, e.g., pe-ripheral device. Since the clocks are not synchronous, the sink needs to buffer received data and avoid loosing data. Also, the sink has to include some type of buffer man-agement protocol to ensure it can adjust for the rate difference between its clock and the source one. When SSC is used, the buffer depth and management protocol has to be able to accommodate significant variable difference between source and sink clock rate. For example, the sink may ignore or insert some bits between transmission packets to adjust the rate difference dynamically. The I/O standard that allow such protocols optionally include DDR2, DDR3, PCI, PCI-X, PCI-Express, Serial ATA (SATA), fully-buffered DIMM (FB-DIMM). The more recent USB3.0 standard includes SSC as a manda-tory feature. Using SSC modulation for other types of I/O that do not include specific buffering features is generally not recommended. SSC clock jitter performance is
often specified using the concept of cycle-to-cycle jitter. C2C jitter is de-fined as the variation of one cycle of a clock signal relative to its adjacent
Figure 4. Main harmonic spectrum for a 125 MHz clock with and without 2% down-spread triangular SSC modulation.
Fair-Rite manufactures a comprehensive line of ferrite components for EMI Suppression, Power Applications, Custom Cores, Ferrite Machining and Antenna/RFID Applications. We have an experienced team of engineers to assist you with new designs. Fair-Rite is the first US soft ferrite manufacturer to receive ISO/TS 16949 certification.
PleasePlease visit www.fair-rite.com to view our online catalog and find a variety of new help tools and search features. You can also easily contact applications engineers, sales representatives, and local distributors. Be sure to bookmark our website as your source for ferrite information.
PO Box 288, 1 Commercial Row, Wallkill, NY 12589 USA(888) FAIRRITE (324-7748) / (845) 895-2055 / Fax (845) 895-2629
Figure 5. First and third harmonic spectrum for a 100 MHz clock with and without 2% downspread triangular SSC modulation.
cycle. Because the SSC modulation rate is typically very low, the impact of the SSC on two adjacent cycles is very similar, and hence their difference is very insensitive to the SSC modulation. It can be shown that the SSC-induced phase modulation is filtered with a filter response that has a 3dB corner frequency and ¼ of the clock frequency and attenuation rate of 40dB/dec at low frequency offset [1]. This ensures that C2C capture the jitter at higher frequency offsets and excludes SSC-induced jitter. As such, it captures the impact of clock jitter in terms of critical path timing more effectively.
V. CONCLUSIONS EMI radiation may result in sig-
nificant interference of one electronic system to other systems close by. To ensure multiple systems can operate properly in close proximity, EMI ra-diation from each system has to meet limits defined by industry or govern-ment bodies. Major EMI reduction
54 interference technology emc test & design guide 2010
emc design / filters CloCk ing Strateg ieS for eMi reduCt ion
Figure 6. Fifth and seventh harmonic spectrum for a 100 MHz clock with and without 2% downspread triangular SSC modulation.
techniques include: 1. Shielding 2. Signal filtering 3. Using solid ground or signal return path
for high-speed signals 4. Reducing rise/fall time 5. Using spread-spectrum clocking (SSC)
modulation The shielding can be costly, and sometimes
difficult to accommodate due to the physical constraints of the system. Signal filtering requires additional board space and compo-nents, and can also increase power consump-tion. Ensuring solid ground is an effective method, which should be followed as a good board layout design practice. However, it is not always a practical solution because it can lead to more ground plane layers, which increases cost. Rise/fall time reduction is a very effective method for reducing EMI at high harmon-ics without increasing power consumption or requiring additional board components. However, such method is only possible if the clock and data buffers and I/Os provide rise/fall time adjustment.
All the methods above are localized to the specific traces. In contrast, SSC modulation
reduces EMI system-wide because the modulation is distrib-uted to all the signal that stem from the SSC clock, regard-less of where that are located. It also reduces EMI at both main harmonics and high harmonics. The main drawback of SSC modulation is that its use is limited to system that use I/O interfaces that include buffer management features required for handling the dynamic rate variations caused by the SSC modulation. For example, it cannot be used for Ethernet and high-speed USB2.0 I/Os.
REFERENCES• [1] Office of Engineering and Technology, “Understanding the FCC
regulations for low-power, non-licensed transmitters”, Federal Com-munication Commission, OET Bulletin, No. 63, October 1993.
• [2] K. Harding, R. A. Oglesbee, F. Fisher, “Investigation into the inter-ference potential of spread-spectrum clock generation to broadband digital communications”, IEEE Transaction on Electromagnetic Compatibility, Vol. 45, No. 1, February 2003.
• [3] H. Skinner, K. Slattery, “Why spread spectrum clocking of com-puting devices is not cheating”, IEEE International Symposium on Electromagnetic Compatibility, 2001.
SASSAN TABATABAEI has held the position of Director of Strategic Applications at SiTime Corporation since 2008. Prior to that, he held executive and technical management positions at Guide Technology, Virage Logic, and Vector12.
He received his Ph.D. from the University of British Columbia, Van-couver, BC, Canada in Electrical Engineering in 2000. n
For most of us, electrostatic discharge (ESD) and static electricity are little more than the shocks received when
touching a metal doorknob after walking along a carpeted floor, or when opening a car door. The level of the voltage produced depends on a number of factors, such as the affinity of the two bodies and the air humidity. Even so, these “harmless” shocks can reach values over 25,000 V.
ESD can be defined as a rapid transfer of charge between bodies at different electrical potentials - either by direct contact, arcing, or induction - in an attempt to become electrically neutral. The human threshold for feeling an ESD is only around 3000 V, so any discharge that can be felt is above this voltage level. Because the duration of this high voltage spike is less than a microsec-ond long, the net energy is small compared to the size of the human body over which it is spread. From the human body’s point of view, ESD does no harm. But when the
discharge is across a small electronic de-vice, the relative energy density is so great that many components can be damaged by ESD at levels as low as 3000 V or even 500 V.
ESD damage can oc-cur at any stage of a component’s life, from
manufacturing to service. For many years it was thought that semiconductor compo-nents such as diodes and transistors were particularly susceptible to ESD, but now we know that passive components such as resistors can sometimes be more sensitive to ESD than active components. Unless spe-cific precautions are taken, a wide range of electronic components can be damaged by ESD. The most common cause of ESD dam-age is direct transfer of an electric charge from either a human body or a charged material to an ESD-sensitive (ESDS) device.
REsIstoRs ANd EsdIn resistors, ESD sensitivity is a function
of size, value, physical construction and thickness. The smaller the resistor, the less space there is to spread the energy caused by an ESD pulse. When this energy is concen-trated in a small area of a resistor’s active ele-ment, and in particular where there is a high current density or “hot spot,” the resistive element may heat up to the point of sustain-ing irreversible damage. With the growing trend of miniaturization, electronic devices, including resistors, are becoming smaller and smaller, causing them to be more prone to ESD damage. Resistance changes due to ESD damage, like load-induced changes, are permanent and can either increase or decrease the device’s resistance value depending upon the resistor’s design and technology.
How smaller Form Factors Exacerbate Esd Risks and
How Foil Resistors Can Help
TABLE 1 - ELECTRICAL SPECIFICATIONS OF FOIL AND THIN FILM CHIPS
PRODUCT TECHNOLOGY
BEST TCR, MIL. RANGE
RANGE OF OHMIC VALUES, ALL CHIP SIZES
Bulk Metal Foil 0.2 ppm/°C 5Ω to 150 kΩ
Thin Film 10 ppm/°C 30Ω to 3 MΩ
56 interference technology emc test & design guide 2010
lightning, transients & esd How Smaller Form FactorS ex acerbate eSD riSkS
Three CaTegories of esD Damage• ParametricFailure:Parametric failure occurs when the
ESD event alters one or more device parameters (resis-tance in the case of resistors), causing it to shift from its required tolerance. This failure does not directly pertain to functionality; thus a parametric failure may be present even if the device is still functional. For example, if a 10 kΩ resistor with a 1 % tolerance undergoes an ESD event that changes its resistance to 11 kΩ (a 10 % deviation), the device would still be able to function as a resistor. But now its parameters have been altered, and it is no longer suitable for its original function. The consequences of such changes may not be immediately apparent but rather may manifest themselves only during circuit tempera-ture excursions, thermal shocks, load life, or any other parametric-shifting influence that would normally be accommodated through error-envelope planning for net accumulated shift limitations.
• Catastrophic Damage: Catastrophic damage has oc-curred when the ESD event causes the device to im-mediately stop functioning. This may occur after one or a number of ESD events with diverse causes, such as human body discharge or the mere presence of an electrostatic field.
• LatentDamage:Latent damage has occurred when the ESD event causes moderate damage to the device, which is not noticeable, as the device appears to be functioning correctly. However, the load life of the device has been dramatically reduced, and further degradation caused by operating stresses may cause the device to fail during service. Latent damage is the source for greatest concern, since it is very difficult to detect by re-measurement or by visual inspection, since damage may have occurred under the external coating.
resisTor TeChnologies anD esD sensiTiviTyDifferent resistor technologies exhibit various levels
of sensitivity to ESD damage. Damage to an ESDS device depends on the device’s ability to dissipate energy and withstand the energy of the voltage levels involved, and in resistors is generally exhibited by a change in the electrical resistance of the device. This is especially crucial in resistors requiring high precision and reliability.
The three most common resistor technologies are Thin Film, Thick Film, and Bulk Metal Foil. Each has specific characteristics related to ESD sensitivity.• ThinFilmresistorsare composed of a metal layer that is
only a few hundred angstroms thick. This severely limits the device’s capability to withstand the energy that is passed through it during an electrostatic discharge, caus-ing it to be very sensitive to ESD damage. As a result, Thin Film resistors are sensitive to energy and can experience value changes of up to 5 % before the ESD causes the film to rupture or to melt.
• ThickFilmresistors are comprised of a random disper-sion of conducting metal particles within a non-conduct-ing particulate medium, usually ceramic; hence they are also known as “cermet” resistors. Current through the resistor follows along the random contacts formed among the metal particles. Power surges cause breakdowns in some of the inter-particulate isolation, thereby reducing resistance by establishing new additional current paths. Thus, ESD surges almost always cause a reduction in re-sistance. This fact is so well established that Thick Film manufacturers use controlled power surges to tune the resistors to the required resistance and tolerance, which typically ranges from 5% to 20%. The susceptibility to change does not stop at manufacture and the resistor is subject to similar changes every time the resistor experi-ences an ESD event. ESD-induced changes while in service can cause resistance changes up to 50%, which is easily sufficient to cause a malfunction.
• BulkMetalFoilresistors have a number of character-istics that make them superior to both Thin and Thick Film when it comes to withstanding ESD. Bulk Metal Foil resistors are comprised of a single layer of special metal alloy rolled into a foil and mounted on a high thermal conductivity ceramic substrate with maximum foil-ceramic interface contact for maximum eduction of heat. As a foil, the molecular structure of the resistance element is the same as the base alloy and therefore has the same metallurgical stability and the same ability to withstand power surges and long-term drift. The foil is 100 times thicker than Thin Film, and therefore the heat capacity of the resistive foil layer is much higher compared to the Thin Film resistive layer.
TABLE 2 - CHIP RESISTOR STYLES, ASSIGNED ESD TEST VOLTAGE AND ENERGY DENSITY
STYLE RESISTIVE LAYER’S DIMENTIONS[1] (mm)
LAYER’S AREA (mm2)
ESD TESTVOLTAGE [2]
(V)
ESD ENERGY [EmJ]
ENERGY DENSITY(E mJ/mm2)
METRIC INCHES
RR1005M RR0402 0.5 x 0.5 0.25 500 0.019 0.076
RR1608M RR0603 1 x 0.8 0.8 1000 0.075 0.094
RR2012M RR0805 1.4 x 1.2 1.7 1500 0.169 0.100
RR3216M RR1206 2 x 1.6 3.2 2000 0.300 0.094
RR5025M RR2010 4 x 2.5 10 3000 0.675 0.068
NOTES: [1] Approximate dimensions of the part of chip’s surface occupied by the pattern, in mm [2] Per draft Iinternational Standard prEN140401-801:200X
Manufacturers test for ESD sensitiv-ity (ESDS) per customer request, but usually do not publish ESDS specifica-tions in their data sheets. However, the ESD of precision chip resistors depends on the following:• Resistive material• Production technology (Thick Film,
Thin Film, or Foil)• Chip size• Ohmic value• Resistive layer’s thickness• Resistor’s construction• Design of the resistive pattern
In testing the influence of above fac-tors, the results depend also on the test method used.
Table 1 shows typical specifications for two main technologies used in production of high precision surface mounted chip resistors: Bulk Metal Foil and Thin Film.
Bulk Metal Foil chips are produced by cementing a nickel-chromium alloy
foil, rolled to a thickness between 2 and 10 microns, to a ceramic substrate. Thin Film chip production involves deposi-tion (by evaporation, sputtering or sim-ilar methods) on a ceramic substrate of a film, mainly nickel-chromium or Tantalum Nitride. A typical thickness of the Thin Film layer is about 1/100 of the Bulk Metal Foil.
Table 2 represents chips which are made in standardized sizes, in rectan-gular shapes. In the middle of the rect-angle is a pattern formed in the resistive layer of foil or Thin Film, connected on two sides to two termination pads.
Tables 3, 4, and 5 show the results of ESD tests on Thin Film, Thick Film, and Foil resistor chips. The superiority of Bulk Metal® foil precision resistors over Thin Film, when subjected to ESD, is attributed mainly to their greater thickness (foil is typically 100 times thicker than Thin Film), and therefore the heat capacity of the resistive foil layer is much higher compared to the Thin Film layer. Thin Film is created
through particle deposition processes (evaporation or sputtering), while foil is a bulk alloy with a crystalline structure created through hot and cold rolling of the melt. Tests show that Bulk Metal Foil chip resistors can withstand ESD events above 25 000 V, while Thin Film chip resistors have been seen to un-dergo catastrophic failures at electric potentials as low as 3000 V and para-metric failures at even lower voltages. If the application is likely to confront the resistor with ESD pulses of significant magnitude, the best resistor choice is Bulk Metal Foil.
ConClusions• When it comes to withstanding ESD,
Foil resistors have a clear advantage over Thin Film chips.
• Foil chips can handle an order of magnitude more ESD energy than Thin Film chips without experienc-ing a change in their resistance.
• The standard for ESD protection in chip resistors ranges from 1 kV to
- 16 and 30kV contact and air discharge- All in one design (no base unit)- Ergonomic design and operation- Touch screen- Modular- Meets all the latest standards- Battery and mains operation- Battery and mains operation- Optical interface- Smart multi-function key
Introducing our latest advancement in EMC technology
The most ergonomic ESD guns on the market, designed to ensure the highest level of comfort when testing, and provide outstanding performance due to the high quality design by the pioneers of EMC test equipment.
Electrostatic Discharge Simulator
58 interference technology emc test & design guide 2010
lightning, transients & esd How Smaller Form FactorS ex acerbate eSD riSkS
TABLE 3 - 2kV ESD DISCHARGE - COMPARISON OF DEVIATIONS, FOIL VS. THIN FILMDISTRIBUTION OF 20 CHIPS BY % OF DEVIATION AFTER ESD DISCHARGE
TYPE AND VALUE >0.5 % 0.2% to 0.5 % 0.1% to 0.2 % 0.05% to 0.1 % 0.02% to 0.05 % 0.01% to 0.02 % <0.01 %
FOIL 30 ΩTF1, 30 ΩTF2, 30 Ω
0120
081
001
002
108
604
1304
FOIL 1000 ΩTF1, 1000 ΩTF2, 1000 Ω
02020
000
000
000
000
000
2000
TABLE 4 - 3kV ESD DISCHARGE - COMPARISON OF DEVIATIONS, FOIL VS. THIN FILM
DISTRIBUTION OF 20 CHIPS BY % OF DEVIATION AFTER ESD DISCHARGE
TYPE AND VALUE >0.5 % 0.2% to 0.5 % 0.1% to 0.2 % 0.05% to 0.1 % 0.02% to 0.05 % 0.1% to 0.02 % <0.01 %
FOIL 30 ΩTF2, 30 Ω
04
010
03
02
11
8-
11-
FOIL, 1000 Ω 0 0 0 0 0 0 20
TABLE 5 - 24kV ESD DISCHARGE - COMPARISON OF DEVIATIONS, FOIL VS. THIN FILM
DISTRIBUTION OF 20 CHIPS BY % OF DEVIATION AFTER ESD DISCHARGE
TYPE AND VALUE >0.5 % 0.2% to 0.5 % 0.1% to 0.2 % 0.05% to 0.1 % 0.02% to 0.05 % 0.01% to 0.02 % <0.01 %
Modular Plug and Play design. Confi gure as needed now, add more circuits later using just a screw driver. No soldering. Ethernet interface with on-board web server and I/P addressing enables computer control from any computer with a web browser, even over your LAN! USB and RS232 interfaces included. Complete solution to IEC 61000-4-16 continuous and short duration test requirements. Full line of AUTO-MATED three phase and I/O line CDN’s up 100 Amps per phase.
Confi gure with available accessories to meet some or all of the following CE MARK requirements:IEC 61000-4-2, -4, -5, -8, -9, -11, -16, -29
EMI & ANTISTATIC PROTECTION
16246 Valley Blvd. Fontana, CA 92334 (909) 829-4444 www.artech2000.com
3 kV, but Bulk Metal Foil resistors can handle ESD pulses up to 24 kV with no significant shift in resistance (measured shifts were less than 0.1 % for a 30-Ω resistor and less than 0.01 % for a 1000-Ω resistor)
• Thin film chips from different sourc-es and with different values show non-uniform behavior with respect to ESD. This may be due to a pattern design that was not optimized for ESD, or a non-uniform film deposi-tion process, or a substrate material that was not of the best quality.
APPENDIXStandards for ESD Testing Of Chip Resistors• The international standard IEC
61340-3-1 describes the testing of electronic components for ESD com-patibility by using the Human Body Model (HBM).
• A test simulator generates an adjust-able voltage ESD pulse by discharging a 150 pF capacitor to the device under
test (DUT) with a discharge resistor of 330 Ω connected in series.
• The ESD exponential waveform which was calibrated with a dis-charge resistance of 330 + 2 Ω will have a time constant which is twice as long when the DUT is a resistor of 332 Ω and much longer with a high ohmic value DUT. Test voltages are listed in table 2. The limit of allowed change of resistance is set for all chip stability levels at 0.5 % + 0.05 Ω.
• RC time constant = (330 + 2) x 150 x 10-12 Ω x (s/Ω) = 49.8 x ns (compared to 150 ns, per ANSI standard).
ENErgy of ESD AbSorbED by A rESIStor ChIP• The ESD is simulated by charging a
capacitor of C = 150 pF to a specified voltage V.
• The stored energy E = 0.5 CV2 is dis-charged into two resistors connected in series: discharge resistor RDIS of 330 Ω representing the resistance of a human body and RDUT - of the DUT,
Over its 27 years ofaerospace lightning-protection services,Lightning Technologies,Inc. has been involvedin the certification ofvirtually every type ofaircraft flying today.
in our case the tested chip. As a re-sult, the following voltage VDUT and energy EDUT are applied to the chip:
• VDUT = V x RDUT /(330 + RDUT)• EDUT = E x RDUT /(330 + RDUT)
rEfErENCES• [1] Thiet The Lai: Electrostatic Discharge (ESD) Sensi-
tivity of thin-Film Hybrid Passive Components. IEEE Transactions on Components, Hybrids, and Manu-facturing Technology, Vol.12, No. 4, December 1989.
• [2] International Standard EN 140401-801:2002• [3] F. Zandman et al.: Resistor Theory and
Technology, SciTek Publishing, Inc. 2002• [4] Technical Note “ESD Sensitivity of Preci-
sion Chip Resistors Comparison between Foil and thin Film Chips” By Joseph Szwarc, 2008
• [5] Vishay Technical Note “Resistor Sensitiv-ity to Electrostatic Discharge (ESD)” By Yuval Hernik 2007
YUVAL HERNIK holds a B.Sc in electrical engineering from the Technion (Israel Institute of Technology). He has been a director of appli-cation engineering at Vishay Precision Group—Bulk Metal Foil resistors—since 2008. n
60 interference technology emc test & design guide 2010
MIL-STD 462/461E CoMparED To MIL-STD461F TEST SET Uptelecom
david a. CaSEcisco systems richfield, oh
In July of 2003, the International Tele-communications Union – Radio adopted Recommendation 229, allocating the
5150-5350 MHz and 5470-5725 MHz bands to mobile service, including RLAN systems .
The following year the FCC updated its Part 15.407 regulations to include the 5470-5725 MHz band, as well as require changes for devices that operate in the 5250-5350 MHz band. As part of sharing the bands with other services on a non-interference basis, the RLAN systems are required to use TPC (Transmitter Power Control) and DFS (Dynamic Frequency Selection), both Cognitive Radio Techniques .
REpoRtEd pRoblEmS in thE fiEld
During discussions on CRS /SDR is-sues at WP5a in late 2008, there was some discussion on RLAN possibly interfering with radar systems despite DFS. However, nothing concrete was presented at these meetings. In April of 2009, it was reported that the FCC was holding up applications for new grants for 5GHz systems specifically in the DFS bands.
In discussions with the FCC lab, the problem told to industry was that there were a number of FAA Terminal Doppler Weather Radars that were being interfered with by RLAN systems and that until the investigation was complete and a possible solution found, no further approvals would
be granted for these systems.Interference was to the TDWRs from
RLAN operating in the 5600-5650 MHz band specifically, as well as some interfer-ence from systems operating on the chan-nels adjacent to this band.
It was discovered that, in some cases, the users could select different country settings and actually turn off DFS; in other cases, the device could only detect the very specific waveforms of the test procedure.
intERim SolutionAn ad-hoc industry workgroup was
formed by interested parties and after a se-ries of discussions with member companies. Since the systems causing the interference were outdoor systems, based on discus-sions with members of the industry, the FCC released in October 2009 an interim procedure for approving master devices operating in these bands indoors.
The requirements for the indoor systems operating in the 5470-5725 MHz are as fol-lows per FCC KDB 443999:
1) The device must not be able to operate on the 5600–5650 MHz band
2) The device must be marketed and sold for indoor use only
3) The information on indoor use only in the 5470-5725 MHz needs to be in the manual or on a label on the device
understanding the Changes to fCC 5 Ghz part 15.407 Regulations
As of October 15, the FCC has turned on the certification process for systems that operate in the 5GHz DFS bands and operate outdoors. Additional information can be found in the FCC KDB 443999.
4) The end user cannot have access to controls set to other regulatory domains or country settings nor be able to turn off DFS
The above FCC KDB allowed the process for indoor-only devices to be turned on and then the focus was on outdoor devices. This issue was addressed in a several tier approach.
The first was that the FAA and FCC were investigating the interference and tracking down these systems. In some cases where either the products were non compliant or that the operator made unauthorized changes, fines were assessed. In cases where the systems were compliant, the systems were set to other frequencies to avoid causing problems.
Second, the FCC issued a Public Notice from OET and Enforcement Bureau asking all manufacturers to reach out to their customers and inform them of this issue. As part of this effort, a voluntary database has been developed that allows operators and installers to register the location information of the UNII devices operating outdoors in the 5470–5725 MHz band when they are installed within 35 km of any TDWR location. The manufacturers are conduct-ing an outreach to their customers as part of this effort to help resolve the interference issues. (See http://www.spectrumbridge.com/udia/home.aspx).
The third solution is to work towards a goal to allow the approvals of outdoor RLAN operating in the 5470-5725 MHz band to go forward. This is being done in a multi-step solution. The first is the interim procedure which is the next revision of KDB 443999. This document was sent out for comments and the comments are now being reviewed by the FCC. The proposal is as follows as extracted from FCC KDB:1. Devices will not permit operation on channels which
overlap the 5600 – 5650 MHz band. 2. Devices intended for outdoor use will be further re-
stricted, as follows: • Devices must be professionally installed when operat-
ing in the 5470 – 5725 MHz band, • Grantees must provide owners, operators and all such
installers with specific instructions in their user’s manual on requirements to avoid interference TDWR and information that meet the following instructions:
• Any installation within 35 km of a TDWR location shall be separated by at least 30 MHz (center-to-center) from TDWR operating frequency (as shown in the attached table), 4, and
• Procedures must be provided for the installers and the operators on how to register the devices in the industry-sponsored database with the appropriate information regarding the location and operation of the device and installer information in that database.
• Devices must meet all of the other requirements speci-fied in Section 15.407, and no configuration controls (e.g. country code settings or other options to modify DFS functions) may be provided to change the fre-quency of operations to any frequency other than those specified on the grant of certification for US operation.
• All applications must clearly show compliance with all of the technical requirements under worse case parameters under user or operator control based on frame rates, listen/talk ratios and user data transfer conditions.
• The next phase will be to develop new radar waveforms for the DFS testing which would test the ability of the systems to detect these TDWR systems. To this effort the industry, the FCC and NTIA are meeting to discuss and review requirements. Further NTIA will be doing some additional testing of the WLAN systems against the new radar wave forms.
As the issues progresses it is best to check with the FCC lab on status of approvals of outdoor systems and also to keep up to date on changes via possibly new FCC KDB’s.
DAVID A. CASE, NCE, NCT, is senior regulatory engineer, corporate com-pliance EMC standards and operations, for Cisco Systems Inc. in Richfield, Ohio. He can be reached at [email protected]. n
Frequency band TDWR >35 km TDWR <35 km
5470-5725 MHz 5600-5650 MHz band off
5600-5650 MHz band off
5470-5725 MHz Registration not required
Register in Database
62 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
Michel Mardiguian Private emc consultant st rémy lès chevreuse, france
The concept of Shield Transfer Imped-ance Zt, introduced by S. Schelkunoff in 1934, is a very convenient pa-
rameter for prediction & control of EMI coupling through cable shields. Although widely applied to coaxial cables against EMI susceptility problems, the Zt pa-rameter can be easily extended to coaxial cables EMI emissions problems, as well as to Shielded Twisted Pairs (STP). This latter is more specifically addressed here, through the concept of Differential Transfer Impedance (Ztd).
i. Brush-up on Transfer Impedance ZtUntil a few decades ago, the Shielding
Effectiveness (SE) of a cable was defined more or less in the same manner as for a Faraday cage or any shielded enclosure, as the ratio of the E (or H) field outside to the E (or H ) field inside. More exactly, the field that would exist at a given point if the shield was not there, to the remaining field when the shield is in place.
In practice, with a shielded cable, the effects of the incident field are measured instead: that is the voltage (or current) in-duced on an unshielded wire illuminated by a given field, to the voltage (or current) on a shielded version of a similar conductor.
Although the principle looks sound and simple, providing a SE figure in dB, the mea-surement itself is not so easy, requiring the
making of a strong electromagnetic field, hence a set of RF amplifiers and antennas, in a shielded - preferrably anechoic- room. Like any radiated EMC measurement, it is plagued with a substantial uncertainty ( typ. 6 dB), aggravated by the fact that below 50MHz, for 1m antenna distance, the test falls in near-field conditions. In such case, the measured SE will depend on the type of antenna being used : E-field illumination will give flattering results, while H-field (loop antenna) will produce overly severe results. Furthermore, test variables like the cable height and its terminating resistors are introducing poorly controlled effects.
In summary, the SE of a same sample, measured by a radiated method could vary widely from one test configuration to another, leaving the user with a SE figure which may not be transposable to his spe-cific application.
Instead of an SE figure which is installa-tion-dependent, the EMC Community has, since long, privileged a parameter that is intrinsic to the cable shield and to nothing else. This is accomplished by the Transfer Impedance (Zt), a brilliant concept intro-duced by Schelkunoff around 1934-38[1].
The transfer impedance relates the current flowing on a shield surface to the voltage it develops on the other side of this surface. This voltage is due to a current coupling through the shield thickness (if the shield is a solid tube, this diffusion rapidly becomes unmeasurable, due to skin effect, as frequency increases) and to the leakage inductance through the braid’s holes. The better the quality of the braid, the less the longitudinal shield’s voltage.
differential Transfer impedance of Shielded Twisted Pairs
64 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
Figure 1. The concept of transfer impedance.
Zt is easy to measure, using a con-ducted injection set-up, less prone to errors and unaccuracies than a radiated test. A current Is (Figure 1) forced on the shield by a generator or current clamp inserted in the cable-to-ground loop. Because of shield imperfections (shield resistance and braiding interstices) a small voltage appears in the inner space between the center conductor and the shield. This voltage, or a fraction of it, is measured at the end of the cable, connected to a Spectrum Analyzer or Oscilloscope input.
The result is normalized to a 1 meter long sample, such as:
Zt (Ω/m) = Vi (Volt) / (Ish x l m) (1)where.Vi = l ongitudinal voltage induced
inside the shield over length « l », causing a noise current to circulate in the center conductor
Ish = external current injected into the shield by the EMI source
If the cable is terminated at both ends in loads RL matched to its char-acteristic impedance, each end takes one half of the full induced voltage Vi. Finally:
Zt (Ω/m) = 2 x VL/ ( Ish x lm ) Typical values of Zt for various
coaxial cables are shown in Figure 2. If the shield is grounded by pigtails (a poor practice) the pigtails impedances must be added to Zt, and to the loop impedance calculations. Below about 100kHz, Zt remains constant, being merely the shield’s ohmic resistance. Above 1 MHz, typically for a single braid, Zt increases with frequency, due to the leakage inductance Lt between the overall braid and the inner conduc-tor. For a good single layer braid, Lt ranges around 1nH /m.
So, Zt can be expressed in the fre-quency domain as:
Zt (Ω/m) = Rsh (Ω/m) + j ωLt (Henry/m)
ii. uSing Zt in SuScePTiBiliTy PredicTion for a coaxial caBle
Initia l ly, Zt was conceived for susceptibility calculations against a known EMI threat, for instance an ambient field illuminating the
Figure 2. Typical values of transfer impedance, Zt.
BEST HAMBURGERS!BEST HAMBURGERS!YOU TRIED THE BEST?
ISN’T IT TIMEEAT WORLDWIDEHAMBURGERSBECAUSE YOUALWAYS HAVE!
EMC Chambers
Built toPerform!Built tobe the Best!
At Braden Shielding Systems, we understand that old habits are hard to break. When it comes to EMC Cham-bers, Braden actually manufactures our equipment in our 50,000 square foot facility. In fact, Braden Shielding Sys-tems has manufactured and installed over 5,000 chambers worldwide.
You can be assured that Braden Shielding Systems can install a chamber in your facility. We maintain an exten-sive list of contractors licenses and state registrations necessary to conduct business. We also keep up to date on laws and regulations in all states.
So the next time you’re ready to eat a hamburger or purchase an EMC chamber, remember: You don’t have to settle for second best just because they sell the most.
66 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
cable-to-ground loop area. The impedance of this external loop, for a single-braid coaxial with an outer diameter in the 5 to 15 mm range, and at a height of 50 to 500 mm above ground can be approximated by:
Zext = ( 10 mΩ + j 5 Ω x FMHz) per meter length (2)If the field-to-loop induced voltage is known, this
ground-loop impedance can be used to calculate the loop current Ish circulating on the shield. Knowing Ish, Zt can then be used straightforward to estimate the voltage ap-pearing inside the shield :
Vi = (Zt x lm) x Ish (3)If the EMI frequency is such as the cable length exceeds
λ/2, then the physical length « l » should be replaced by λ/2 in the bracket term of Equation 3.
Example 1:A 4m single braid coaxial cable, installed 0.75m above
ground, is illuminated by an ambient RF field of 10V/m @ 15MHz, causing 9V of open loop induced voltage. What is the voltage appearing at the receiver end of the cable?
External loop impedance, calculated by Equation 2: Zext = (0.01 + j 5 x 15 MHz) x 4m = 300ΩThe calculated loop current is: Ish = 9V / 300Ω = 0.03AFor a single braid coax. like RG58, Figure 2 indicates Zt
@ 15MHz = 0.15Ω/m. The induced voltage on the coax center conductor is: Vi = Zt x l m x I = 0.15 x 4 x 0.03 = 18mVAssuming that the cable is terminated in 50Ω both ends, VL = 18mV x 50 / (50 + 50) = 9mVIf the receiving endwas terminated in a high impedance,
like 5kΩ : VL = 18mV x 5000 / (5000 + 50) ≈ 18mVIncidentally, one could grade the reduction factor gained
via the shield as the ratio of the loop bulk voltage to the voltage appearing internally:
Kr = 9V / 18.10-3 V = 500, that is 54dB
ii. uSing Zt for PredicTing radiaTed rf eMiSSionS froM a coaxial caBle
The principle of Zt is perfectly reciprocal and can be ap-plied to emissions as well. RF signals, baseband video, some LAN links and other high-frequency signals are carried over coaxial cables. A very small fraction of the intentional signal current (typically 0.3 to 0.1 percent above a few MHz) returns by paths other than the shield itself (Figure 3). This assumes that the shield is at least correctly tied to the ground references at both ends, and preferably also to the chassis by the coaxial connectors.
The signal current I0 returning by the shield’s inner side is causing an EMI voltage to appear along the outer side.
Figure 3. Principle of coaxial cable driven into radiation.
68 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
This voltage is given by: Vext = Zt (Ω/m) x l (m) x I0 (4) = Zt (Ω/m) x l (m) x V0 / ZLIn turn, this voltage Vext is causing an external current
to excite the antenna formed by the cable-to-ground loop, hence radiating a small field that can be associated with the quality of the shield and its installation.
For estimating the E and H field from this low-imped-ance loop (see Figure 4), the external shield current can be found by:
Iext = Vext / Zextwhere Zext is the same as the one calculated for suscep-
tibility case. Eventually, pigtail or connector impedances have to be incorporated into Zext. Although their contribu-tion to Zext is usually minimal, they can seriously deteriorate the shield transfer impedance, since Zt must be hundreds or thousands of times smaller than Zext, for a good shield.
If the shield is floated from the chassis, the shield be-comes an electrically driven radiator. The radiated field can be calculated using monopole or dipole equations, with Vext, as an input.
When the cable becomes electrically long, Zt (Ω/m) no longer can be multiplied by the length, since the current is not uniform along the cable shield. A default approximation is to consider that the maximum amplitudes of the shield voltages distributed along the shield are:
Work directly with the leading U.S. manufacturer of EMI shielding. Tech-Etch offers a complete line of standard and custom products.
EMI/RFI Shielding Solutions
RoHS compliant Metalized Fabric Gaskets provide excellent shielding with very low compression forces and less than 3% compression set.
Board Level Shielding manufactured using photoetching eliminates the expense of forming tools, plus improves design fl exibility and delivery time.
Honeycomb Vents use lightweight extruded aluminum frames for increased strength. Many standard designs are available, plus custom designs.
TECH-ETCH, INC., 45 Aldrin Road, Plymouth, MA 02360 • TEL 508-747-0300 • FAX 508-746-9639
Fast DeliveryTech-Etch maintains a large inventory of standard fi ngerstock shielding for immediate delivery. In addition, an extensive free sample program enables functional testing of the part specifi ed. Samples typically ship in a few days.
Expert Customer ServiceExper ienced Customer Serv ice Representatives provide fast computerized quotations. Product Engineers are always available to assist in product selection or answer shielding questions.
Download New Interactive PDFEMI Shielding Products CatalogInteractive 52-page Catalog lets the user jump from page-to-page with a click of the mouse and even download interactive sales drawings of over 150 shielding products including BeCu gaskets, metalized fabric, fan vents, and board level shielding. A printed version is also offered.
Made in USATwo state-of-the-art facilities in Massachusetts are ready to manufacture your next order.
RoHS compliant Fabric Gasketsexcellent shielding with very low compression forces and less than 3% compression set.
Board Level Shieldingmanufactured using photoetching eliminates the expense of forming tools, plus improves design fl exibility and delivery time.
Honeycomb Vents lightweight extruded aluminum frames for increased strength. Many standard designs are available, plus custom designs.
the part specifi ed. Samples typically ship in a few days.
Interactive 52-page Catalog lets the user jump from page-to-page with a click of the mouse and even download interactive sales drawings of over 150 shielding products including BeCu gaskets, metalized fabric, fan vents, and board level shielding. A printed
Two state-of-the-art facilities in Massachusetts
BeCu Fingerstock Gaskets are offered to close gaps as narrow as .010". Tech-Etch manufactures over 120 standard profi les for immediate delivery.
Figure 4. Equivalent circuit to predict coaxial cable radiation.
Vext (max) = Iext. Zt (Ω/m) x λ/2 (5)So, as Zt increases with frequency, the effective length
which multiplies Zt decreases with frequency. At the same time, the cable-to-ground external impedance needs to be replaced by ZC, the corresponding characteristic imped-ance, using the following formula:
ZC = 60 logn (4h/d) (6)Example 2A 2 meter piece of RG-58 coax is connecting two
cabinets, with BNC connectors at both ends. The electrical parameters are:
Useful signal: 15 MHz video Load resistance: 75Ω V0 spectrum amplitudes: fundamental (15MHz) = 10 Vpk harmonic #3 ( 45MHz) = 3.3 Vpk harmonic #5 ( 75MHz) = 2 VpkThe geometry is:Cable diameter= 0.5 cm, height above ground = 30 cmCalculate the radiated field at 3 m due to harmonic #3. SolutionFirst, we need to determine the area of the radiating loop: A = 2 m x 0.3 m = 0.6 m2 = 6,000 cm2
For 45MHz, λ = 6.70m, so the 2m length of cable is already exceeding λ/4 , approaching λ/2. We can consider that the radiation efficiency of the antenna formed by the
shield-to-ground loop has reached its maximum asymptote.For a same reason, the external loop impedance is
approaching its maximum, that is the characteristic impedance :
ZC = 60 log n (4 x 30 / 5) = 330 ΩThe internal signal current returning by the shield is: I0 (45MHz) = V0 /75 Ω = 3.3 / 75 = 44mAThe external shield voltage, due to transfer impedance
Zt is : Vext (45MHz) = I0. Zt(Ω/m) x 2m, where Zt (45MHz) is given by Figure 2 = 0,4 Ω/m Vext = 44.10-3 . 0.4 . 2m = 35. 10-3 VThis voltage, in turn, is driving an external current onto
the loop:Iext = Vext / ZC = 35. 10-3 V / 330Ω = 107.10-6AFrom this current, the radiated field at 3 m (far field
conditions) can be quickly estimated [2] by : E (µV/m) = [ 1.3 . Acm2 . Iamp . F(MHz) 2 ] 1/D E (µV/m) = 560 µV/m , or 55dBµV/m(*Note: Since the whole calculation has been carried
in peak values, 3dB should be subtracted for peak-to-rms conversion, but they are apprximately offset by the ground plane reflection of the CISPR/FCC test set-up.)
Although this radiated level is about 500 times lower than if a bare wire were carrying the same current with a return by the ground plane, FCC Class B limit is exceeded
Custom Shields and Metal Parts. Fotofab’s process of photochemical etching offers speed, flexibility and
precision unmatched by traditional manufacturing methods.
q Print to part in 1 day - yes we’re that fast!
q Fotofab’s technical staff will drive your project - even without a print.
q Complex features, non-standard sizes and company logos are free.
q Fotofab can form, plate and package your parts...
Just tell us what you need!
You’ll see the difference as soon as you talk to us. Contact our sales staff today, or request your free shielding sample kit and design guide at www.fotofab.com/shielding
773.463.6211 3758 W. Belmont Avenue FAX.463.3387 Chicago, IL 60618 [email protected] USA
A World Apart In a World of Parts!
70 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
by 15 dB @ 45MHz, with other limit violations at 75, 105 MHz and so on.
Several possibilities exist to reduce the radiated field: • Select a coaxial cable with a lower Zt, like “optimized”
braided shields (thicker, denser braid) or double-braid shield.
• Slip a large ferrite bead over the cable shield. It will take an added series impedance of about 1,200Ω to achieve the required attenuation, for instance passing the cable twice into a large ferrite toroïd.
• Reduce the cable height above ground.
iii. iMPorTance of The Shield connecTionSAs important as a shield with low Zt is its low-impedance
termination to the equipment metal boxes. The connection by which the shield itself is grounded to the equipment box (or PCB) has its own impedance, too.
This impedance consist of the shield-to-backshell con-tact, the connector-to-receptacle impedance (that may include some seam leakage inductance) and the receptacle-to-chassis contact resistance.
This connection impedance Zct is directly in the signal current return path, in series with Zt. Therefore, Zct can increase seriously the voltage Vext, which excites the cable-to-ground radiating loop. At contrast with cable
shield Zt which is a distributed parameter (Ω/m), Zct is a localized element.
Of course, if the shield is grounded by a piece of wire, or « pigtail » ( a very poor practice), the connecting impedance is simply the self-inductance of this wire tail.
The following Table values can be taken for typical impedances of one single shield connection:
Ni/Al technology is available as a silicone based elastomer gasket (CHO-SEAL® 6502), fluorosilicone based elastomer gasket (CHO-SEAL® 6503) and form-in-place silicone based thermal cure gasket (CHOFORM® 5560). Please contact Chomerics Application Engineering support team for product performance information. Chomerics, a division of Parker Hannifin Corporation, is a global supplier of EMI Shielding, Thermal Management, Display Enhancement Filters and Engineered Thermoplastic solutions. Our worldwide network of Applications Engineering support, manufacturing facilities, and sales offices insures Chomerics products are available when and where you need them.
CHO-SEAL® 6502 & 6503Chomerics’ new nickel plated aluminum(Ni/Al) filled elastomer technology reduces galvanic corrosion by >50% while providing higher and more stable EMI shielding when compared to silver plated aluminum technology. Ni/Al will reduce field inspection and repair costs while improving reliability in any end use environment.
Silver/Aluminum filled EMI Gasket 500 Hours Salt Fog Exposure on Trivalent Chromate Treated Aluminum
CHO-SEAL 6503 Ni/Al EMI Gasket 500 Hours Salt Fog Exposure on Trivalent Chromate Treated Aluminum
System EMC specifications require a Bulk Cable Injection (BCI) test: 200mA rms, 30MHz – 200MHz
What will be the differential voltage seen at the receiving end?Solution
Calculations are carried at 100MHz, which is about the worst case frequency region for 0.80m cable length.
1) Zt for a single braid @ 100MHz (Figure 2): 1Ω /mCorresponding Ztd for 5% unbalance : 5.10-2 Ω /mVdm for 0.80m cable ( Equ.7) : Vdm = 0.80 . 1 Ω /m.
5.10-2 x 200mA = 8 mVrmsSince fast digital circuits (receivers, comparators) tend
to respond to the peak value of modulated RF, the actual EMI voltage will be:
Vdm = 8.√2 = 11 mV, augmented eventually by a modula-tion coefficient.
Thus, based on shield coupling alone, the received volt-age is 20dB below the LVDS detection threshold
2) The STP is terminated by plastic RJ45 plugs, with the shield grounded both ends via 12.5mm ( 0.5’’) pigtails. What is the new value of Vdm?
The total self-inductance for two pigtails ( typ. value 1nH/mm) is:
Lp = 2 x 12.5 x 1nH = 25nHCorresponding parasitic impedance added in series to
Zt, at 100MHz: Zp = Lω = 16ΩNew value of Vdm, with the contribution of 2 pigtails
(taking into account a same 5% unbal. as for the pair) Vdm = [(0.80 . 1 Ω /m . 5.10-2) + 16 . 5.10-2] x 200mA
iV. The differenTial TranSfer iMPedance (Ztd) wiTh Shielded PairS or MulTiconducTor caBleS
The concept of transfer impedance, used for radiated susceptibility or emission modeling of a coaxial cable, is transposable to shielded twisted pairs (STP). However, there is a noticeable difference: the shield is no longer an active return conductor.
4.1 Susceptibility prediction using Ztd for a shielded pair
The induced voltage Vi appearing in the shield (see Figure 5) due to the loop current is not directly seen as a differential voltage across the wire pair. Two situations may arise:
a) General caseIf the link is a true balanced one, using differential driv-
ers / receivers and wire pairs, we can start from the voltage Vi appearing inside the shield due to the loop induced cur-rent Ish (see Equation 3).
Each wire 1 and 2 is exposed to the same voltage Vi, such as if the symmetry was perfect, the difference Vi(1) – Vi(2) would be null. Since there is a certain percentage of unbalance in the wires resistances, capacitance to shield and leakage inductance vs the shield, the differential volt-age will be :
Vdm = Vi . X% . RL / (Rs + RL)where X% is the unbalance percentage of the pair. De-
pending on the quality of the balanced link, X may range anywhere from 1 to 10 percent, with typical (default) value being 5 percent, for high speed data links.
Thus, replacing Vi by its expression for a coaxial cable configuration, we get:
Vdm = [Zt (Ω/m). l (m). I sh] . X% (RL/ (Rs + RL)) (7)We can therefore define a Differential Transfer Imped-
ance Ztd that will include the shield Zt times the pair un-balance, augmented eventually by the shielded connector Ztc and its own unbalance ( the contacts balance vs the metallic connector shell is not perfect either and can dete-riorate the whole link symmetry). This new parameter Ztd will allow a single pass calculation of Vdm, from a given sheath current.
b) Case of unbalanced links using a STP.If the associated Transmitter // Receiver circuits are of
the unbalanced type (single-ended), without Bal.to. Unbal. conversion devices, one wire of the pair will be tied to the 0V reference at both ends and the whole STP behaves as a pseudo-coaxial link. The only small advantage being that the return wire dc resistance is paralleling the cable shield, or that the Electronic Reference ( 0V) could be eventually floated from chassis, yet the shield being chassis-grounded. Example 3
A high speed differential link is using a STP, with following parameters :
Figure 5. STP equivalent circuit for susceptibility to field coupling and its mode conversion inside the shield.
72 interference technology emc test & design guide 2010
shielding Different ial transfer impeDance of shielDeD twisteD pa irs
= 170 mVrms, or 235 mVpkThis is more than twice (6dB) the
LVDS detection threshold. The pigtails have deteriorated the transfer imped-ance of a fairly good braid by more than 20 times ( 26 dB). Metallic connectors insuring an integral shield grounding are necessary.
4.2 application of Ztd to an eMi radiated emission case
With true differential links using differential drivers / receivers and wire pairs, the current returning by the shield is only prorated to the percent-age of asymmetry in the pair. If the transmission link is balanced with X percent tolerance, the unwanted share of current returning by the shield is, for the worst possible combination of tolerances, only X% of the total current.
In this case, Equation 4 becomes: Vext = X% . Zt (Ω/m) x l (m) x
V0 / Z L (8)Thus, the radiated field is reduced by
a factor equal to X percent, compared to a coaxial cable situation.
To the contrary, if the wire pair is interfacing circuits that are not bal-anced (e.g., the signal returns being grounded at both ends), a larger por-tion of the signal current will use the shield as a fortuitous return, like with case 4.1.b). This portion is difficult to predict. At worst, this unbalanced configuration cannot radiate more
than the coaxial case.Example 4Using the same high speed differ-
ential link as example 3, calculate the field radiated at 3m by the fundamental component of a 100MHz data stream, with following parameters:
(4 x 75 /0.5) = 380ΩExternal current driven into the
cable-to-ground loop by Vext: Iext = V ext / Zc = 0.7.10-6 ALoop area = 80 x 75 = 6000 cm2
Radiated field at 3m ( see Example 2) E (µV/m) = [ 1.3 . Acm2 . Iamp
. F(MHz) 2 ] 1/D E (µV/m) = 18 µV/m, or 25
dBµV/mThis is about 22 dB below the FCC
Class B limit.If the shield grounding was made
by the same pigtails as example 3, their deterioration of Ztd would raise the field to 380 µV/m ( 51.5 dBµV/m) exceeding the limit by 5 dB.
V. acTual MeaSureMenTS reSulTS wiTh good qualiTy eTherneT STP
Figure 5 shows an example of un-balance measurements on an Ethernet type STP. Such measurements require a rigorous instrumentation set-up to prevent parasitic effects from obscur-
ing the results. For instance, the Balun transformer, converting the symetrical 100Ω outpout to the unbalanced 50Ω input of the Spectrum Analyzer, must have at least a balance 14 dB better than the best pair being evaluated. This would just grant a < 2dB uncertainty of the results.
referenceS• [1]. Schelkunoff, S. Electromagnetic Theory
of coaxial lines and cylindrical shells, Bell Syst. Technical Journal, 1934
• [2]. Mardiguian, M. Controlling Radiated Emissions by Design, 2nd Edition, Kluwer Academics, 2001
MICHEL MARDIGUIAN, IEEE Senior Mem-ber, graduated electrical engineer BSEE, MSEE, born in Paris, 1941. After military service in the French Air Force, worked for Dassault Avia-tion, 1965 to1968. Moved to the IBM R&D Lab. near Nice,France, working in the packaging of modems and digital PABXs.
Mardiguian started his EMC career in 1974 as the local IBM EMC specialist, having close ties with his US counterparts at IBM/Kingston,USA. From 1976 to 80, he was also the French delegate to the CISPR Working Grp on computer RFI, participating to what was to become CISPR 22, the root document for FCC 15-J and European EN 55022. In 1980, he joined Don White Consultants (later re-named ICT ) in Gainesville, Virginia, becoming Director of Training, then VP Engineering. He developed the market of EMC seminars, teaching himself more than 160 classes in the US and worldwide. n
Figure 7. Measured results for good quality STP. The balance is better than -40dB up to 30MHz, the worst unbalance being – 30dB ( 3%) at 100MHz. (Courtesy of Alain Charoy, AEMC / France)
74 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
PhiliP KeeblerKermit PhiPPsFranK sharPePri lighting laboratory
introduction
For years, lighting systems have been operating as stand-alone loads with-out the use of sophisticated lighting
controls for energy savings in all types of facilities—residential, commercial, and industrial. Utilities and end users viewed lighting controls in the past as, luxury, sys-tems that were used only when mood or spe-cial effects lighting was needed. Although two industries—broadcast and theatrics—have relied on dimmable lighting and basic lighting control systems for years as a part of their stage and set lighting, systems were very simple and traditionally dimmed only incandescent lamps. Other types of light sources were either not dimmable or did not provide the color performance needed for television cameras or live audiences.
Today, however, the need to provide dimmable lighting systems in more types of customer spaces is different today. With the help of lighting designers and energy researchers, end users are finding more ap-plications for dimmable light sources paired with more sophisticated lighting control systems. Dimming is no longer limited to incandescent and electronic f luorescent systems. Dimmable lighting device designs are finding more application in electronic
high-intensity discharge (HID), induc-tion, and LED devices and other advanced lighting systems. Lighting researchers are discovering more ways to optimize lighting levels in various spaces by incorporating the use of dimmable light sources and lighting control systems. Commercial facilities are probing deeper into new applications for dimmable light sources and lighting control systems in efforts to improve energy savings. Some installations are even making better use of outdoor light as they strive to harvest as much daylight as possible to offset their energy usage for lighting systems. Utilities are experimenting with various dimmable light sources and various types of lighting control systems through EPRI demonstra-tion and other projects while examining customer perceptions, how much energy savings can be achieved without interrupt-ing the customers’ business, and verification of savings before rebates and incentives are issued.
The federal government and other sup-porters of green initiatives are putting pressure on building designers, utilities, and end users to improve energy savings in various types of facilities. Lighting is one of those load types where energy savings is very achievable, and if implemented cor-rectly, can be employed without introducing lighting and power quality problems into customer facilities. With lighting represent-ing as much as 23% of the grid load, with many customer spaces characteristic of over illuminated conditions, and, to utilize
system compatibility: an essential ingredient for achieving electromagnetic
compatibility and Power Quality for lighting control systems
110
405
10
210
1
CALIFORNIACALIFORNIA
2011 IEEE International Symposium on Electromagnetic Compatibility
August 14-19, 2011 • Long Beach Convention Center
Call for Papers EMC 2011 is a Technical
Symposium. Technical Papers
are the essence of our Technical
Program. Original,
unpublished papers on all
aspects of electromagnetic
compatibility are invited.
*Late papers will NOT be accepted.
Preliminary Full Paper Manuscript: November 1, 2010 - January 15, 2011
Acceptance Notification: March 15, 2011
Final Paper and Workshop/Tutorial Material Due: May 1, 2011
Important Dates
www.emc2011.org
76 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
daylight to offset the need for electric lighting, there is much opportunity to reduce energy usage and demand with the use of dimmable light sources and lighting control systems.
Utilities and customers alike who do engage in using dimmable light sources and lighting control sys-tems do so today with many res-ervations and concerns. They are aware of some problems that have occurred when pairing dimmable light sources with lighting control systems in common everyday electri-cal environments. Several of these problems resulted from compro-mised lighting device and controls performance caused by poor power quality (PQ) and poor electromag-netic compatibility (EMC).
Utilities and customers expect new systems to work well together and to function properly in their expected electrical environments regardless of facility type. Lighting control systems should function properly regardless of what other neighboring loads are used in a facility. When compat-ibility problems occur with lighting devices and/or control systems, even lighting problems can grossly affect the customer’s business operations regardless of which type of lighting device—fluorescent, HID, or LED—is used. Some problems are severe enough to cause facility shutdown until action can be taken to disable the lighting control system. These problems can result in lost downtime and re-installation costs that can add up to the thousands of dollars.
The complexity of these systems and the demand for complete func-tionality warrants the need for im-proving the compatibility between lighting devices and control systems and their electrical environments. Utilities and end users must endure increased pressure to improve build-ing performance and reduce lighting energy costs while controlling facility budgets.
This art icle seeks out to de-scribe the importance of achiev-ing compatibility between lighting devices and control systems and the electrical environment while
understanding PQ and EMC barri-ers that typically occur with lighting devices and control systems. Past EPRI research in the area of system compatibility has been applied to many types of electronic lighting devices. The application of EPRI's system compatibility concept can be used for lighting control systems not only to document energy, emissions and immunity performance, but to harden lighting controls systems and to continue hardening electronic lighting devices.
comPatibility Problems with lighting controls
Regardless of the type of commu-nication link used to communicate with controllable light sources, their networks spread out across a facility and penetrating the electrical and electromagnetic environment.
Lighting control systems may use various types of communication links in essentially all types of lighting devices—fluorescent, HID, and LED:
• Hard-wired, low-voltage, 0 – 10 volt DC, analog control
(Digita l ly Addressable Lighting Interface) control.
Each method of communication requires dedicated electronic circuits inside the lighting device. Penetration of the communications circuit inside the lighting device further exposes the other electronics inside the lighting device to malfunction and upset. For example, when an electrical fast tran-sient (EFT) is coupled into a lighting control circuit, this voltage anomaly is carried to the electronic inside the lighting device.
The electrical and electromagnetic environment can both interact with each of these communication systems to cause any of the following compat-ibility problems, all of which have been witnessed in the field by EPRI and various end users.• Inability to turn light source on
when an ‘on’ command is sent• Inability to turn light source off
when an ‘off’ command is sent• Inability to dim light source up
(increase intensity) when a ‘dim up’ command is sent
• Inability to dim light source down (decrease intensity) when a ‘dim down’ command is sent
• Complete malfunction of lighting controller (light sources will not respond to any end-user initiated commands)
• Unstable operation of light sources (flickering lamps, random turn ‘on’, random turn ‘off’, etc.)
• Complete failure of lighting controllerThe sources of electrical and elec-
tromagnetic disturbances that can affect lighting controls include many types of industry defined waveform disturbances and random waveform disturbances that extend from a few tens of hertz up to hundreds of megahertz. Such disturbances can be generated from a wide variety of end-use equipment and operation of electrical equipment inside a residen-tial, commercial or industrial facility. Although the number of disturbance sources is not as many in residential settings as in commercial and indus-trial settings, the types of equipment that can generate these disturbances in residential settings is increasing as end users acquire more non-linear electronic loads like high-definition televisions and electronically con-trolled appliances including those with adjustable speed drives (ASDs). Example sources include the following
• Transients generated by the switch-ing ‘on’ and ‘off’ of large loads such as heat pumps, refrigerators, ovens, pumps, washers, dryers, etc., and even induction cooking appliances
• Conducted noise generated on the power line by electronic loads in-cluding electronic lighting devices using electronic ballasts and by failing power supplies in comput-ers, audio and video equipment, and in gaming equipment
• Voltage notching generated by the operation of highly-inductive loads (appliances that contain ASDs and motors)
Some people read ENR just for laughs...
But most of our subscribers just like to know
what’s happening in the EMC community
Electromagnetic News ReportFor 38 years in Print
and now also Online Subscribe today
www.7ms.com/enr
78 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
Figure 1. Example of lighting control system with multiple circuits.
Figure 2. Electrical and electromagnetic disturbances that can impinge upon a lighting controller.
ITEM™
introducingEnvironmental Test & Design (ETD)
shock
temperature
HALT
waste
sustainability
vibration
acoustics
eco design
HASS
news
standards
compliance
A new electronic newsletter that focuses on the inter-rela-tionship between electronic products, systems and devices and their environments.
Visit www.interferencetechnology.com to subscribe today
Find out more: Bob Poust, ETD Business Development [email protected] | 484-688-0300 ext 15
ETD is published by ITEM Publications
ETD coverage will include: » The impact of shock, vibration, temperature and
acoustics on electronic products, and how they are de-signed to withstand these influences.
» The impact of electronic products upon their environ-ments in terms of acoustical noise, vibrations, and other emissions.
» Qualification and analysis of electronic products from a lifecycle perspective and the use of HALT, HASS, ESS testing and other screening methods.
ITEM™
ETD_ECSM10.indd 2 6/30/2010 5:02:42 PM
80 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
• Voltage distortion generated by increasing penetration levels of electronic appliances that inject harmonic cur-rents into the customer wiring system
• Electrical noise on the branch circuits generated by radiated emissions from radio transmitters, wireless devices, etc.
• Transients (surges) generated by thunderstorms and light-ning strikes and also transients picked up by automatic lawn sprinkler systemsMoreover, with the use of lighting controllers there is
another opportunity for control system upset caused by radiated transients and high-frequency radiated emissions that can also be coupled onto any one of the hard-wired communications links. The thousands of feet, or miles (in some cases), of control cable is exposed to electric fields generated by transients and emissions and may cause distortion or corruption of control signals. In almost all cases, these cables are either not shielded or contain the very minimum amount of cable shielding due to the added expense of shielded cables.
Figure 1 illustrates the basic concept of the primary ports commonly used on a lighting controller and how they can act as entries for electrical and electromagnetic disturbances. The line input port is a line-voltage power port usually rated at 120 volts AC but may also be rated at a universal voltage (e.g., 120 to 277 Vac) or higher AC line voltage (e.g., 230 Vac) in European applications. The dimming control ports (four shown in Figure 1, other controllers may have fewer or more of these ports) are low-voltage ports and usu-ally rated for up to 10 volts DC. These ports deliver a very small power to the dimming control circuit of a dimmable lighting device. Most lighting controllers have two or more sensor ports which may be used to support one or a series of remote sensors located somewhere out in a facility at a considerable distance from the controller. In Figure 1, these are the photocell (daylight sensor) port and the occupancy sensor port. To operate these sensors, a separate DC supply voltage is required—usually 12, 15, or 24 volts DC. The com-munications port is also a low-voltage port, but for network signals where multiple conductors which can be Ethernet,
Table 1. Cross-reference between electrical and electromagnetic disturbances and malfunctions or failures of lighting control systems.
1 Dimming port, sensor port, or other low-voltage port2 Includes ring wave, combination wave, capacitor switching, and electrical fast transients (EFTs)
Malfunction or Malfunction or Failure with Lighting Controls
RS-232, or RS-485 are used. The wireless port is one that is showing up more on lighting controllers. This port and the network port(s) may be of an open (e.g., Zigbee) or closed architecture.
exPosure to electrical and electromagnetic disturbances
A lighting controller installed in a facility, whether the facility is a residential, commercial, or industrial one, is subject to the same exposure to electrical and electromag-netic disturbances as any other piece of networked elec-tronic equipment (e.g. a computer) which also uses control and signals ports and control cables. Figure 2 illustrates several scenarios where disturbances can impinge upon the hard-wired and wireless ports of any lighting controller used to control any lighting device—fluorescent, HID, or LED. Each port essentially has some susceptibility to these disturbances, and this susceptibility will, at some level and frequency, cause the lighting controller to malfunction, be upset, or be damaged. The question is “How susceptible are lighting controllers to the electrical and electromagnetic disturbances that commonly occur in the customer’s elec-trical (facility) environment?” The only way to definitively determine their susceptibility is to test them in a controlled laboratory environment capable of generating industry standardized, random, and field documented disturbances.
cross-reFerencing disturbances and Failures with lighting control systems
Because of the nature of lighting control systems and the electrical and electromagnetic disturbances that occur in environments where multi-port systems must live, there is significant opportunity to improve their performance. Per-formance improvements are based on which disturbances impact which part of a lighting control system and the severity of the malfunction or upset. Obviously, any dis-turbance that causes permanent damage must be resolved without delay. Table 1 lists various types of malfunctions
and failures that may occur with lighting controls. Each one of these has occurred in the field as reported by utilities, various manufacturers and end users. Some of these may be resolved with a system reset and some require hardware replacement. Others may require a circuit enhancement in the lighting controller to improve the immunity of the system to a specific disturbance. Regardless, these present
Figure 3. MOV failure caused by thermal runaway and internal equipment fire in a lighting controller.
Figure 4. MOV failure caused by thermal runaway and internal equipment fire in another lighting controller.
Tri-Mag, Inc. can build standard and custom design EMI filters for any industry:
MEDICAL, MILITARY & INDUSTRIAL
In addition to our wide range
of standard products and
our capabilities of building custom
products to fit any application, all of Tri-Mag, Inc. Filters are
built in the USA.
ROHS Compliance
1601 N. Clancy Ct. Visalia, CA 93291 • Phone: (559) 651-2222 • Fax: (559) 651-0188www.tri-mag.com • [email protected]
82 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
problems to the end user that will likely interrupt the nature of their business and function of the lighting control system. In some situations, the interruption will present safety issues to the facility or its occupants as well.
Discussions with manufacturers of lighting controls and end users who have installed them in the past several years have revealed that the nature of compatibility problems as listed in Table 1. Compatibility problems are indeed occur-ring and increasing with some communication methods. The good news is that the performance of lighting control systems can be improved with the application of EPRI’s System Compatibility concept. The increase in compatibility problems among lighting control systems can be attributed to four causes: 1) the increased complexity of lighting con-trol systems (i.e., more use of electronic microcircuits and more use of low-voltage ports for network, control and signal functions, 2) the increased complexity of the electrical and electromagnetic environments where systems are installed, 3) the increased frequency of use (i.e., end users are using them more often in applications where lighting control is needed or required to meet certain specific energy savings goals) of lighting control systems, and 4) the increased development of new electronic lighting devices and their increased use.
One area where failures have increased is in the protec-tion of the AC power port against voltage surges. In visu-ally inspecting MOV failures in lighting controls, thermal runaway has been increasingly observed. Thermal runaway may occur if an MOV with too low of a maximum allowable voltage is applied in lighting control equipment in efforts to provide protection against voltage surges. In such a case, an MOV’s exposure to a long-term overvoltage may be higher than the MOV’s maximum allowable voltage, and thermal runaway of the MOV may occur without blowing the line fuse. Figures 4 and 5 show two examples of MOVs in light-ing controllers, which failed as a result of thermal runaway. In both examples, the MOV ignited and a significant part of the MOV material was burned by the fire caused by its own thermal runaway. The fire from the MOV damaged other nearby electronic components and the enclosure for the lighting controller. If investigators discover this type of MOV failure surrounded by other burned insulation and electronic components, then thermal runaway can be sus-pected. These susceptibilities, or weak links in the design of these lighting controllers, can be identified through compat-ibility analysis and testing at the EPRI Lighting Laboratory.
system comPatibility and Power QualityWhat is a power quality problem? Imagine this. . . . The
fluorescent lights connected to a lighting controller in a manufacturing facility blink, indicating that the voltage has briefly dipped. A split second later, the high-intensity discharge (HID) lights drop out, adjustable-speed drives that control process motors trip, and scrap material gathers on the floor of the now dimly lit manufacturing facility. A few minutes later, the indoor LED lighting devices begin to oscillate, causing the illumination to rise and fall slowly. Or
this. . . . Lightning strikes near a telemarketing facility. The uninterruptible power supplies connected to the computer systems switch on, but some of the computers lock up, dis-rupting data processing and vaporizing data. The light from the overhead dimmable fluorescent lighting system fades as about one-third of the fixtures go out. Or perhaps you don’t have to imagine if you use magnetic HID ballasts with metal halide lamps and have been left in the dark for 15 to 20 minutes before the lamps cool down enough to restrike. Imagine this type of problem when your lights are con-nected to a lighting controller. The lighting controller is in full command of the lights, but the lights cannot be turned back on because the controller already says they are on.
Every year, problems with electricity and electrical equip-ment cost U.S. companies billions of dollars in scrap mate-rial, down time, damaged data, and delayed orders. Every year, electric utilities produce and deliver almost two billion cycles of electricity. If just a few of those cycles are disturbed, computers in commercial offices may crash, industrial equipment may shut down, and entire processes may grind to a halt. Moreover, equipment in one facility may cause other equipment in the same facility or in a neighboring facility to malfunction, even when the quality of delivered power is perfect. With lighting controls, which are embed-ded within a facility’s electrical system, these problems be-come even more compounded. Each wired port on a lighting controller is a “door” for an electrical or electromagnetic disturbance to enter the controller. With facilities becoming more cluttered with electronic equipment, the frequency of occurrence for disturbances, their disturbance levels (both low and high frequency) are increasing. As buildings become more intelligent, more compatibility problems will surface and render equipment inoperable.
aPPlying Power Quality and comPatibility to lighting controls
Power quality is the concept of powering and grounding electronic equipment in a manner that is suitable to the opera-tion of that equipment as defined by the IEEE Standard 1100, The Emerald Book. (Early EPRI research in the area of system compatibility provided many contributions to this publica-tion.) Power quality is a concept that was developed to study and improve the quality of electric power as it is generated, transmitted, and distributed to utility customers and consum-ers by electrical and electronic equipment.
Manufacturers and consumers often misapply the defini-tion of power quality. Without even a basic understanding of power quality, they often think of quality power as power that contains absolutely no imperfections. Mistakenly, they apply the same thinking to lighting controllers as well as electronic lighting devices. Similarly, an electrical engineer unfamiliar with the power quality concept may think of quality power with a ‘perfect sine wave’ with no irregular waveshapes or distortion whatsoever and a data string as a perfect stream of zeroes and ones. Both of these are incorrect perceptions of power quality as the input power to lighting controllers and the data they must deliver and receive contain artifacts
resulting from the occurrence of electri-cal and electromagnetic disturbances in customer facilities.
Figure 5 illustrates a rising data pulse captured on a port of a lighting controller that receives a command from a daylighting sensor. This pulse is supposed to be a digital zero tra-versing to a digital one (e.g., 0 volts traversing to 5 volts) in an attempt to activate dimming of a bank of dim-mable lighting fixtures connected to one of the dimming ports of a light-ing controller. The pulse contains high-frequency conducted noise. This noise has entered the control cable that runs from the controller to the daylight sensor with timing and am-plitude characteristics limits set by the manufacturer. The cable was shielded, but the shielding material failed. The shield did not reduce the noise current in the shield that resulted from the in flux of a high-frequency radiated elec-tric field present in the building. The electric field was generated by a set of input power cables running from an electrical panel to the input of a set of adjustable speed drives.
Because these emissions are associ-ated with the electrical branch circuit inside a building. The operation of the ASDs (i.e., a non-linear load), created the problem on the branch circuit. This is considered to be a system compat-ibility problem. The quality of the voltage on this circuit is corrupted by the presence of these high-frequency emissions.
Because the lighting controller is susceptible to these emissions, the controller is deemed to have a com-patibility problem with its common
everyday electrical environment. One might ask, are these emissions really common in a commercial or industrial electrical environment where the com-patibility problem occurred? All ASDs produce some conducted emissions on their input circuitry which travel out of the ASD up the branch circuit. The emissions levels among ASDs do vary with ASD manufacturer and model as well as the impedance and length of the branch circuit and some other variables. These emissions were being coupled into the daylight sensor con-trol cable as the cable was run in paral-lel and too close to the branch circuit powering the ASD. One could remove the problematic lighting controller and replace it with one that had the exact same design (i.e., same input power requirements, same types of lighting control channels with the same day-lighting control functions) and this problem may never have occurred.
The immunity of the daylight sensor input when used with a specific control cable and daylight sensor will vary among lighting controller. However, in this case the problematic lighting con-troller has an immunity low enough to allow this problem to occur while other controllers had a higher immunity to these emissions at these frequencies.
The lighting controller was rendered inoperable as a result of this compat-ibility problem and was removed from the facility. This indicates a couple of major points for concern: 1) the shield-ing of the control cable was insufficient to protect the data signal inside the cable from the radiated electric field and 2) the port of the lighting control-ler could not filter out this noise in the
data signal and caused the controller to lockup.
In order to better understand power quality and system compatibility and how it can be applied to the charac-terization of end-use equipment like lighting controls, EPRI has developed a detailed concept called system com-patibility which can be applied to any electronic device including lighting controls. A series of system compat-ibility tests can be applied to a light-ing controller to determine its energy, emissions, and immunity performance for each power and signal port and the product as a whole.
An EPRI test procedure exists which allows each type of electrical and elec-tromagnetic disturbance to be applied to the proper ports of a lighting control. The low-frequency disturbances are derived from definitions for each type of voltage variation and disturbance that occurs on the power system and inside customer facilities. These defini-tions, which are now standardized and part of an IEEE standard 1159-1995 (R2001), IEEE Recommended Practice for Monitoring Electric Power Quality, were in part developed through actual power quality studies conducted at EPRI on various power systems across the United States in the last 15 to 20 years. Through having developed a thorough understanding of power quality, power system engineers and system compatibility engineers (en-gineers who study the compatibility between the power system and end-use electrical and electronic equipment) have been able to determine how equipment responds to each type of variation and disturbance.
what is system comPatibility?
When equipment and appliances get along in the same electrical en-vironment, they are said to be in a state of system compatibility. System compatibility is defined as the abil-ity of a device, equipment or system, generally a load, to function satisfac-torily with respect to its power-supply electrical environment without intro-ducing intolerable electrical distur-bances to anything in that environ-
Figure 5. A rising data pulse (going from zero to one) corrupted with conducted noise.
84 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
ment. However, in today’s complex and diverse electrical environment, achieving system compatibility is of-ten a steep challenge for any product designer, especially for multiport sys-tems like lighting controllers where compatibility must be applied to each port. For example, modern industrial processes rely on sophisticated elec-tronics for precise and continuous process control, and malfunction and upset of these electronics can jeop-ardize process reliability. Industrial plants that rely on process reliability also rely on quality lighting control systems. When these plants apply demand response, utilities will be relying on reliable communication and operation of lighting control sys-tems to shave load when required to ensure power system stability. Com-mercial facilities are characteristic of the same types of disturbances and operation of disturbance-generating loads l ike ASDs more commonly
used in heating, air-conditioning, and ventilation systems. An increasing number of lighting controllers rely on feedback from daylighting sen-sors spread throughout a facility to determine what appropriate levels of light are needed in task areas where sensors (and windows) are located.
There is more to the quality of a lighting system than measuring the photometrics of the light. A quality lighting system includes the following, some of which are directly influenced by a lighting controller. These general performance requirements are not only important to lighting controllers but are also important to demand response activities. Demand response requests will utilize lighting controllers to ini-tiate commands to make adjustments in lighting loads by turning dimmable lighting devices ‘on’ or ‘off’ or change dimming levels.
If disruption to a lighting controller occurs in a demand response applica-
tion, the controller may or may not initiate the request properly. Moreover, the controller (or a separate monitoring device) may or may not be able to verify that the request was actually carried out. A situation where a request called for the dimming of certain lights may actually have occurred, but verification of that request indicated otherwise. The converse problem may also occur. Regardless, compatibility problems with lighting controllers may leave the utility (and the customer) in a state of unknown when it comes to load reduc-tion and energy savings.
PhotometryCompatibility can also impact the
photometrics of a lighting system. In lighting control applications, it is important that a dimmable lighting device response as intended to a light-ing control command. A compatibility problem may cause a lighting control system to render one of the follow-ing problems to a dimmable lighting device.
• Providing an unstable arc (dis-charge) inside an HID lamp at some dimming level because the wrong dimming level was reached
• Providing a sable DC current for an LED fixture (a driver function)
• Providing an incorrect amount of foot-candles targeted toward an area where the light is needed
• Providing an incorrect color of light where light of a different color is needed
• Making an inappropriate adjust-ment (too low or too high) light levels based on how much ambient light enters a room or space
safety, compatibility, and Power Quality
Safety must be the first priority in any facility regardless of the busi-ness activity. Reliable and compatible lighting systems play a vital role in maintaining safety. Lighting devices and lighting control systems which are not compatible with the electrical environment will increase the risk of an accident occurring. Aside from in-creased efficiency, one of the primary benefits of using electronics in lighting
Figure 6. The design process with integrated system compatibility testing.
devices is to enhance safety-related performance. However, if the elec-tronic ballast (or driver) is not compat-ible with the electrical environment, then safety-related performance will likely be compromised. Listed below are some examples of why lighting is critical to safety. • Keeping the lights on when they
are needed• Minimizing the number of lamp
drop outs• Maintaining as much lumen output
for the life of the lamp as possible – called lumen depreciation – to avoid light levels that are too low before lamps reach the end of their expected life
• Avoid ing lamp f l icker as the load inside and outside a facility changes – f lickering lamps may cause rotating machinery to ap-pear 'standing still '
compatibility, reliability and economics
Electronic lighting devices and light-
ing control systems require a capital investment. To reap the return on investment (ROI), projected costs must be maintained within their estimate to avoid stretching out the pay back period. Pay back periods for lighting upgrades usually run from about one year to as long as three to four years depending on a variety of factors. Uti-lization of lighting controls typically shortens the pay back period. Listed be-low are examples of some cost-related expectations:
• Maintaining efficacy (efficiency) for the expected life of the ballast and lamp or the driver and LED
• Achieving enough lamp and bal-last or LED and driver reliability to achieve a return on the investment that the customer has made in pur-chasing and installing the modern lighting system
• Ensuring that the lighting control system of an electronic ballast or electronic driver remains fully op-erational over the life of the ballast/driver so that lighting load can be
adjusted according to customer needs or the utility’s desire to reduce peak load in future demand response applications
Each of the above categories involves the use of a lighting control. Considering a few examples, the first two categories in the above list are centered around the lamp and the fixture. The next two bullets are related to the performance of the lamp-ballast or LED-driver system. This performance also depends on how the lamp-ballast or LED-driver system responds to variations or disturbances in the AC line voltage powering the lighting system.
EPRI research indicates that LED-driver systems combined with lighting controls may be more susceptible to common everyday electrical and elec-tromagnetic disturbances than lamp-ballast systems combined with the same controls. When the customer makes an investment to purchase and install a modern lighting system such as one that uses high-frequency HID or LEDs, that customer expects the system to operate
Figure 7. Compatibility concept applied to lighting controller, demand response system, and overall system.
86 interference technology emc test & design guide 2010
Achiev ing eMc, Power QuAl it y for l ight ing control SySteMS power quality
reliably. Reliable operation should last for at least a minimum of the warranty period. The warranty period offered by the lamp, ballast and fixture manufac-turer will likely be different. The lighting specifier, retrofitter, and/or installer can help one understand the nature and design of warranties and their periods. A severe electrical event, such as a near lightning strike, high voltage distortion, or a larger than expected number of sags may occur during the warranty period. Manufacturers may not honor the war-ranty if extreme events occur. Power-line monitoring of the lighting branch circuit, a facility power quality audit, and/or a forensic analysis on a failed ballast (or driver) or lighting control-ler by EPRI may reveal the cause of an early failure. If the facility environment reaches a high ambient temperature, the lamp and ballast (or LEDs and driver) life may be shortened possibly causing premature failure.
Why Apply SyStem CompAtibility to lighting SyStemS?
Traditionally, lighting systems from the days of Thomas Edison were of the incandescent type. No energy conversion device was needed between the power system and the lamp, and no lighting controls were used. This does not mean that disturbances in the power system did not affect incandescent lamps. This simply means that the incandescent lamp is under direct influence of disturbances that occur on the power system. Compat-ibility tests conducted on incandescent lamps have shown that the reliability of lamp filaments are affected by dis-turbances such as voltage sags, voltage swells, and voltage surges. With respect to the end user, a change in illumination is usually noticeable with these distur-bances until the lamp fails to produce light when the filament is severed. With lighting control systems, failures and malfunctions in lamps are also possible and can actually be initiated by malfunc-tions in lighting controllers.
Early f luorescent-based lighting systems were developed by leading manufacturers soon became popular lighting products for end users of all types. These systems through the use
of a magnetic ballast were connected to a fluorescent lamp. The purpose of a ballast is to produce enough energy to ignite a lamp and then control its illumination through either voltage or current control.
In magnetic f luorescent lighting systems, the magnetic ballast is a simple core-and-coil type of device with no sophisticated electronic components for controlling lamp performance. These ballasts also respond to various types of steady-state and transient power-line disturbances. With vary little voltage regulation built into a magnetic ballast, the ballast will allow an increase in illu-mination with an overvoltage or a voltage swell and a decrease in illumination with a voltage sag. However, the core and coil of a magnetic ballast system have the distinct advantage of having a more-than-acceptable immunity to voltage surges.
Although this type of immunity helps to increase ballast reliability, end users often complain about issues other than ballast failures such as noticeable variations in light fluctuations. These fluctuations in light output are called lamp flicker. All types of lamps and lamp-ballast systems have their own characteristic response to various types of voltage fluctuations—the type of line-side disturbance that causes lamp flicker.
Lamps and lamp-ballast systems may act as amplifiers of voltage fluctua-tions or they may act as attenuators to fluctuations. Each component of the lamp-ballast system plays a different role in determining the extent to which the lamp-ballast system acts as an amplifier or attenuator of fluctuations. When acting as an amplifier, a small fluctuation incident on the AC input of a lamp-ballast system, for example, will result in a large change in light output. The same is true for lighting control-lers—disturbances initiated at the line input may find their way through the lighting controller and into the signal that controls the light output of elec-tronic ballasts.
With respect to end users, each hu-man eye also has a distinct frequency response to lamp flicker. Some people can notice a lamp f lickering when others cannot. Some will indicate
that what may be defined by some as a mild lamp flicker will actually cause severe headaches, thus prevent-ing users from functioning in a work environment. This is because their perception to lamp flicker varies from person to person. Lamp flicker studies have been conducted on many types of incandescent and fluorescent lamps and ballasts with the results varying among lamp and ballast models as expected. As more lighting systems become electronic, lamp flicker stud-ies will continue to gain more atten-tion, especially for systems operating at higher lamp wattages such as HID lamps where a small amount of flicker in a fluorescent lamp may not be very noticeable as compared to that same amount of flicker in an HID lamp that may be more noticeable.
While the human perception-related performance issues in lighting systems can gain much attention from utility customers, professionals in the lighting industry traditionally focus on lamp and ballast performance and reliability. These professional groups include architects, lighting specifiers, facility electrical designers, lighting engineers, and lamp and ballast de-signers. Each of these groups strives to provide acceptable lighting systems for their customers that meet their expectations in terms of lamp and bal-last performance and reliability. Each strive to 1) provide lighting systems that maintain acceptable light output for the majority of the life of the light-ing system and 2) provide lighting systems that function at an acceptable level for at least the term of the product warranty.
Manufacturers of electronic fluo-rescent ballasts learned about perfor-mance and reliability the hard way. Many of them did not understand the whole-system performance: how to design a high-frequency inverter type of power supply, populate a printed circuit board with components rated for an elevated operating tempera-ture, solder them to the board, place that board inside a metal can, pour hot potting material over the circuit, and install it into a lighting fixture. Many lessons regarding circuit design,
component reliability, soldering, speci-fications, and potting were learned. With some knowledge about ballast reliability and the warranty term, many manufacturers did not have enough data to reasonably design and specify their warranty programs. Both manu-facturers and end users experienced significant financial losses from poor lamp and ballast reliability.
Many have asked how system com-patibility testing could have prevented much of these financial losses. At the time when the first electronic fluo-rescent ballasts were being designed, component manufacturers were also not familiar with applying their devices in ballasts. Component engineering combined with a temperature-based compatibility study might have helped reduce the number of failures cause by the overheating of electronic compo-nents. Compatibility testing would not have had much of an effect on manu-facturing defects including soldering. However, during many of the forensic studies that were conducted on failed electronic fluorescent ballasts, it was found that disturbances which would not normally affect a well-designed electronic ballast would have a much more negative effect on the perfor-mance and reliability of a ballast with design problems. Disturbances such as voltage transients and voltage sags were found to cause premature failure of ballast circuits and the component lead-to-solder joint junction. Compat-ibility testing on such samples prior to production would have resulted in the identification of ballast reliability issues prior to the installation of thou-sands of ballasts that eventually failed when powered in a normal electrical environment.
For these reasons, manufacturers and end users of electronic ballasts, whether they produce or use fluores-cent, HID lamp-ballast, or LED sys-tems, must have a keen awareness of the compatibility of these systems with the power system. Many are integrat-ing compatibility testing into their ballast design processes with the goal of identifying compatibility problems long before the start of production. EPRI has worked with dozens of ballast
manufacturers and applied the com-patibility concept to their products. Manufacturers of LED drivers and LED lighting systems are just begin-ning to recognize the importance of EPRI compatibility testing for their products. If lighting controls are to be a key part of a facility’s lighting system to help reduce energy usage, then the same needs to happen for all lighting controllers.
Figure 6 illustrates the design pro-cess with integrated system compat-ibility testing. This process served as the guideline during the development and testing of the many electronic bal-last products. Lighting control design-ers can learn to apply the compatibility concept (See Figure 7) just as easy as ballast manufacturers have done. The process is basically the same, but the results will be different and just as valuable.
How Compatibility EnablEs ligHting Control to bE DEmanD rEsponsivE
With basic lighting controllers having been developed several years ago, some with fairly mature designs, many controllers will continue to be used as individual systems separate from demand response (DR) systems. However, while the compatibility of a DR system is just as important as the compatibility of a lighting control system, the overall compatibility of a combined DR-lighting control system will be critical for facilities that begin to rely on them. Figure 7 illustrates this concept. Interestingly enough, many of the lessons to be learned regarding compatibility for lighting controllers will also be applicable to DR systems.
ConClusion: systEm Compatibility is important for ligHting Controls
As stated earlier, lighting controls are becoming a key part of a facility’s operating system. Prior to the use of lighting control, lights in a facility were just turned ‘on’ at the beginning of a day and turned ‘off’ at the end of a day. Now, facilities are having to become more intelligent and vary light levels according to occupant usage, space
purpose, and ambient light levels. If facilities are to engage in energy sav-ings using lighting controls, then the controls that they use must be hard-ened to the point where facility man-ages and occupants can expect them to function as desired in all types of electrical environments and building operating conditions. The electrical environment of the facility, including emissions and disturbances generated by the lighting devices themselves, must not impact the operation of light-ing control systems.
Lighting controllers will need to function during thunderstorms, during electrical disturbances initiated by the public, and during electrical distur-bances initiated by the utility. Lighting control designers may even want to consider integrating intelligence into the control that alerts the end user when an adverse condition exists such as the presence of a high level of electri-cal noise on one of the communication or port channels. Resolving a compat-ibility problem with a lighting control-ler before it shuts the building lighting system down would be very valuable. EPRI maintains expertise in solving compatibility problems with lighting controls. Expertise in this area can be used to further understand compat-ibility problems with lighting devices and control systems. End users simply cannot work in the dark, or under poor lighting conditions and in some condi-tions the failure of a lighting control system would present safety problems requiring the building to be evacuated. EPRI is positioned to further the ma-turity of lighting devices and controls through its research and testing in its Lighting Laboratory.
Philip F. Keebler manages the Lighting and Electromagnetic Compatibility (EMC) Group at EPRI where EMC site surveys are conducted, end-use devices are tested for EMC, EMC audits are conducted and EMI solutions are identified.
Kermit O. Phipps is a NARTE Certified engi-neer and conducts tests and evaluations of equip-ment performance in accordance with the EPRI System Compatibility Test Protocols for EPRI.
Frank Sharp is a Senior Project Engineer / Scientist at EPRI in Knoxville, Tenn. n
88 interference technology emc test & design guide 2010
AdvAnced TesT equipmenT RenTAls. 30
AgilenT Technologies 17
Ah sysTems, inc. inside fRonT coveR
AmeRicoR elecTRonics, lTd. 54
AR Rf/micRowAve insTRumenTATion 1, 15, inside bAck coveR
AR Tech engineeRed fAbRic pRoducTs 58
bRAden shielding sysTems 65
cApToR coRpoRATion 53
chomeRics, div. of pARkeR hAnnifin coRp. 70
com-poweR coRp. 5
cpi - comm & poweR ind. 9
csT - compuTeR simulATion Technology 3
em TesT usA 43
emc pARTneR Ag 39
emi filTeR compAny 53
enR / seven mounTAins scienTific 77
eTc - elecTRonics TesT cenTRe - kAnATA 45
fAiR-RiTe pRoducTs coRp. 52
filTemc elecTRonic equipmenT co., lTd 51
foTofAb coRp 69
goRe 12, 73
hAefely emc division 57
heilind elecTRonics, inc. 61
hv Technologies, inc. 58
ieee emc socieTy symposium 75
ifi insTRumenTs foR indusTRy 40, bAck coveR
inTeRmARk usA 51
iTem publicATions 41, 79, 82, 87
kimmel geRke AssociATes lTd. 31
lichTig emc consulTing, llc 31
lighTning Technologies inc 59
mAcTon coRpoRATion 13
mesAgo messe fRAnkfuRT gmbh 7
miTsubishi gAs chemicAl compAny, inc. 35
monTRose compliAnce seRvices 31
nolATo silikonTeknik Ab 66
pARTneRship foR defense innovATion 11
peARson elecTRonics, inc. 30
ppm lTd. (pulse poweR & meAsuRemenT) 27
quAlTesT 31
RAdius poweR 50
ReTlif TesTing lAboRAToRies 25
schuRTeR inc 49
specTRum AdvAnced speciAlTy pRoducTs 47
spiRA mfg. coRp. 63
swifT TexTile meTAlizing 67
Tech-eTch, inc. 68
Teseq 37
TRi-mAg 81
zeRo gRound 72
when you conTAcT ouR AdveRTiseRs, pleAse RemembeR To Tell Them you sAw TheiR Ad in inTeRfeRence Technology.
REQUEST INFORMATION FROM OUR ADVERTISERS
index of advertisers
Everybody Talks Quality,We Think Seeing Is Believing.
rf/microwave instrumentationOther ar divisions: modular rf • receiver systems • ar europeUSA 215-723-8181. For an applications engineer, call 800-933-8181.In Europe, call ar United Kingdom 441-908-282766 • ar France 33-1-47-91-75-30 • emv GmbH 89-614-1710 • ar Benelux 31-172-423-000
Lots of suppliers claim to make “quality” products. But does quality still mean what it used to mean? It does at AR.
Over more than 40 years, we’ve built a reputation for reliable products that go the distance. (And then some). Products that are faster,smaller, and more efficient. Products that outlast, outperform and outrun any in the category. And every one backed by worldwidesupport and the best no nonsense warranties in the industry.
The way we see it, quality is about results. If a product can’t cut it in the real world, you won’t get the answers you need. And wewon’t get the loyal customers we need.
So here’s to companies and customers who still respect – and demand – quality.
EMI Receiver•No dials, no switches and no buttons to deal with.
•CISPR compliant, meets MIL-STD,automotive requirements and DO-160.
Newer A Series Amplifiers 10 kHz - 250 MHz, up to 16,000 watts.
•Broader frequency bandwidth - test to all standards. •25% to 50% smaller - can fit in your control room.
•Units have superior hybrid cooling system technologywhich provides greater reliability and lifespan.
Newer S Series Amplifiers 0.8 - 4.2 GHz, up to 800 watts
•Smaller and portable. •Better performance with increased efficiency.
•Linear with lower harmonics and 100% mismatch capability.
RF Conducted Immunity Test Systems3 Self - contained models with integrated power meter and
signal generator. Frequency and level thresholding for failure analysis.
Subampability™: (sub-amp-ability). noun: The ability to use an amplifier individually, or as a building
block, upon which power can be added incrementally.
New ATR26M6G-126 MHz - 6 GHz, up to 5000 watts
•High input power capability for stronger radiated fields. •60% smaller than standard log periodics.
•Meet most of your testing needs with one antenna.
Traveling Wave Tube Amplifiers•Provides higher power than solid state (CW and Pulse).
•Frequency ranges up to 45 GHz.•Sleep mode - preserves the longevity, protects the tube.
AS Systems •Everything you need in one comprehensive test system.
•On the shelf or customizable solutions.•Broadest range of equipment available from one company.
W Series Amplifiers DC - 1000 MHz, up to 4000 watts
•Subampability: expand from 1000 Watts to 4000 Watts over time.•Intelligent amplifier - self diagnostic.
•Reliable
Hybrid Modules• Power up to 37 dBm from 6 to 18 GHz.
•Excellent linearity, gain and flatness.•Use as a building block anywhere in your design.
•Customizable in our in-house, state-of-the-art microelectronics lab.
World’s Largest Selection of Field Probes•Widest frequency range available- 5 kHz to 60 GHz.
•Incredibly small, never requires batteries.•Improved mechanical mounting and axis labeling.
•Detects fields from 2 V/m to 1000 V/m.•Automatic noise reduction and temperature compensation.
Horn Antennas•Full selection from 200 MHz to 40 GHz.
•Power up to 3000 Watts. •Retain the bore sight.
•Make height and rotational adjustments on the fly.•Saves time, saves money, retain testing accuracy.
