THE ELECTROMAGNETIC REVERBERATION CHAMBER AT NASA JSCField Uniformity Testing and Calibration

ABOUT THE INTERN• Oregon State University: B.S., Philosophy

• San Francisco State University: M.S., Physics

• University of Connecticut: Ph.D., Physics

(in progress)

• EMI Intern by trade

• Hobbies include

• Travel

• Photography

• Quantum Field Theory

EV5: ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY• EMI/EMC test facilities at JSC provide evaluation and certification testing of

crew, flight, and ground support equipment including: Communication, Instrumentation, Biomedical, Guidance and Navigation, Computation, and Robotics.

• Electrical and electronic equipment aboard a spacecraft can malfunction or become totally inoperable if not designed to properly minimize the effects of interference from the internal and external electromagnetic environments. Proper equipment and system designs are also necessary for minimizing potential electromagnetic emissions into the operating environment.

THE REVERB CHAMBERPhysical Characterization and Relevant Parameters

THE REVERB CHAMBER

Dimensions: 3.07 x 3.07 x 2.46 meters

Lowest Usable Frequency: ~240 MHz (100 modes)

Installed

Equipment: Tuner

Step Motor

Transmit Antenna

Calibration

Equipment: Field Probe

Receive Antenna

RF Absorbers (loaded chamber)

Closed Cell Styrofoam Test Bench (loaded chamber)

THE REVERB CHAMBERA BIG “MICROWAVE OVEN”

• Transmit antenna sets up EM fields in chamber

• Tuner position determines EM boundary conditions

• Averaging measurements over tuner rotation washes out “hot” and “cold” spots

• Rigid coordinate system

• Field Probe and Rx antenna positions• 9 positions (8 for loaded chamber)

• Probe axis orientation vs chamber coordinate axes

REVERBERATION CHAMBER TESTING: BENEFITS

• Allows equipment under susceptibility test to be exposed to RF radiation isotropically (from all directions)

• Radiated emissions will be picked up regardless of any directional bias in emissions

• Allows for automated testing without switching out antennas/varying polarizations

• Depending on the application, test frequency step granularity may be coarser than (semi-)anechoic alternative offering faster test times

• Susceptibility testing emulates realistic aircraft operating environment more faithfully than (semi-)anechoic methods

INSTRUMENTATION

• Signal Generator

• Amplifier

• Directional Coupler

• Power Sensors/Meter

• Spectrum Analyzer

• Field Monitor

• Control PC

• Motor Controller

INSTRUMENTATION• Signal Generator

• Amplifier

• Directional Coupler

• Power Sensors/Meter

• Spectrum Analyzer

• Field Monitor

• Control PC

• Motor Controller

RC CALIBRATION AND TESTING STANDARDS

IEC 61000-4-21

• terminology, descriptions of electromagnetic phenomena and the EM environment, measurement and testing techniques, and guidelines on installation and mitigation

MIL-STD-461

• establishes interface and associated verification requirements for the control of the electromagnetic interference (emission and susceptibility) characteristics of electronic, electrical, and electromechanical equipment and subsystems designed or procured for use by activities and agencies of the Department of Defense

RTCA DO-160F/G

• establishes interface and associated verification requirements for the control of the electromagnetic interference (emission and susceptibility) characteristics of electronic, electrical, and electromechanical equipment and subsystems designed or procured for use by activities and agencies of the Department of Defense

DO-160F REQUIREMENTS

• Field Uniformity Requirements

• Test Frequency Spectrum Resolution (50 freq. per decade)

• Receive power and field strength measurement regimen

• Field strength data verifies field uniformity

• Received power measurements provide baseline Antenna Calibration Factor used in determining necessary injected power for equipment test

• Suggested maximum loading (16 dB)

• # of tuner steps (frequency dependent)

CALIBRATION AND TESTING

Empty Chamber

• Field Uniformity Verification

• Antenna Calibration Factor

Loaded Chamber

• Field Uniformity Verification

• Antenna Calibration Factor

Equipment Test

• Pretest Chamber Calibration Factor

(injected power determination)

• Emissions and Susceptibility Test

TILE RC CALIBRATION PROFILE

1. Initialize Instrumentation

2. Sweep test frequency range

3. Export data (power/field strength measurements) to .csv

4. Increment Tuner

5. Repeat 1-4 50 times for 1 revolution

6. Move probe/Rx antenna

7. Repeat 1-5

Note: TILE! v.6 has no versatile loop capability

MOTOR CONTROLLER COMMAND SEQUENCE

• Anaheim Automation Motor Controller “Direct Talk” Mode

• VISA interface

• Acceleration/Base speed important

• Line break syntax

TILE! REVERBERATION CHAMBER CALIBRATION DIALOGUE

TILE! TABLE: OUTPUT TO .CSV FILE

• Test Frequency

• Electric field strength: components and RMS (Watts/m)

• Forward/Reverse/Net Injected Power

• Received Power

• Signal Generator Amplitude

DATA PROCESSING TEMPLATES

0

1

2

3

4

Empty Chamber Field Uniformity

SD Ex

SD Ey

SD Ez

SD x-y-z

Frequency (MHz)

E-f

ield

Sta

nd

ard

De

via

tio

n

(dB

m)

EMPTY CHAMBER DATA

EMPTY CHAMBER DATA

100 200 300 400 500 600 700 800 900 1000 1100

-25

-20

-15

-10

-5

0

Empty Chamber ACF

Frequency (MHz)

AC

F (

dB

)

ACF =

Average power received divided by average power transmitted

(averaging performed over tuner positions)

EMPTY CHAMBER DATA

Rayleigh curve gives probability distribution for field strength of statistically independent rectangular components of multiply scattered EM waves

THE LOADED CHAMBER

• DO-160F suggests loading the chamber to obtain a factor of 12 (16 dB) degradation in ACF

• Obtained an average of 7 dB decrease with significant loading

0

1

2

3

4

Loaded Chamber Field Uniformity

SD Ex

SD Ey

SD Ez

SD x-y-z

Frequency (MHz)

E-f

ield

Sta

nd

ard

De

via

tio

n

(dB

m)

LOADED CHAMBER DATA

LOADED CHAMBER DATA

100 200 300 400 500 600 700 800 900 1000 1100

-35

-30

-25

-20

-15

-10

-5

0

Loaded Chamber ACF

Frequency (MHz)

AC

F (

dB

)EMPTY CHAMBER DATA

~7.3 dB average decrease from empty configuration

PROBLEMS AND SOLUTIONS

ISSUE 1: TILE POWER DATA ELEMENTS

BUG

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

f(x) = 1.00320884614238 x − 0.000383708363932533

Reverse Power TILE vs manual measurement

TILE Reverse Power (Watts)

Mea

sure

d R

ever

se P

ower

(W

atts

)

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.80.99

1

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

Forward Power TILE vs Manual Measurement

TILE Forward Power (Watts)

Man

ual F

orw

ard

Pow

er (

Wat

ts)

1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.080.99

11.011.021.031.041.051.061.071.08

f(x) = 0.973994049122435 x + 0.025108889955122

Forward Power TILE vs Net Power Manual Measurement

Forward Power Tile (Watts)

Net

Pow

er M

anau

l (W

atts

)

RESOLUTION• Recognize TILE! Forward Power data

element as Net Power record

• Ignore TILE! Net Power data element

• If Forward power is needed, compute as difference of reverse and net power

THREAT LEVEL: LOW (SIMPLE USER END FIX)

ISSUE 2: FIELD MONITOR BECOMES

UNRESPONSIVE

• Field Monitor occasionally becomes unresponsive

• Monitor screen goes blank and TILE! starts reading zero for electric field components and RMS

RESOLUTION• Spot check TILE! dialogue and

field monitor readings frequently

• In case of failure, locate failure point in .csv file (signaled by null probe readings)

• Delete data for tuner steps with null results

• Reboot TILE! and reinitialize test phase at appropriate tile

THREAT LEVEL: ANNOYING(EASY TO PREVENT BY SPOT MONITORING BUT

TIME CONSUMING IF UNNOTICED)

ISSUE 3: STEP MOTOR SLOP

• Step motor advertised as having 1.8 degree step size

• Slop observed to be at least on this order (partially due to mechanical tuner fixture)

RESOLUTION

• Spot check tuner position on occasion

• Tuner increment step size larger than observed slop

• Ensure large sampling size

• Averaging over probe positions should wash out problems

• Eliminate mechanical fixture contribution

THREAT LEVEL: UNADVISABLE LONG TERM (INTRODUCES AND PROPAGATES UNNECESSARY ERROR)

ISSUE 4: MOTOR CTRL FAULTS RESOLUTION

• Motor controller occasionally faults and ceases operation

• TILE! Routine continues collecting data unaware

• Spot check motor controller to ensure FLT light is off and PWR light is green

• In case of fault:

1. Abort Test Sequence

2. Isolate failure point in .csv (signaled by repetitious field probe readings for subsequent tuner positions (~1V/m similarity)

3. Delete these repeated data sets from .csv

4. Clear motor controller error using the “Clear Motor Ctrl Error” tile or by power cycling the controller

5. Reinitialize test sequence at point of failure

THREAT LEVEL: MODERATE(WHILE EASY TO AVOID BY CONSISTENT SPOT

CHECKING, FAILURE CAN BE TIME CONSUMING TO CORRECT IF LEFT UNNOTICED)

ISSUE 5: TX ANTENNA FIXTURE

• Transmit antenna should be permanently affixed to chamber

• Movement or alteration of position and alignment voids calibration

RESOLUTION

• Temporary: Tape

• Long Term: Solutions forthcoming

THREAT LEVEL: LOW (CURRENT CONFIGURATION IS RELATIVELY RIGID: DO NOT BUMP)

ISSUE 6: ANCIENT LAPTOP RESOLUTION

• Forthcoming

THREAT LEVEL: LOW TO MODERATE(DATA BACKUP WILL AVOID

CATASTROPHIC CONSEQUENCES, BUT RISK OF SUDDEN INTERRUPTION TO OPERATIONAL CAPACITY IS NONTRIVIAL)

FUTURE WORK

• Continue development and implementation of EUT TILE! profile

• Continue certification process for chamber

• Integrate Anaheim motor controller driver into TILE! (whenever it arrives)

• Calibrate at higher frequencies with horn tx antenna (fewer probe/rx antenna positions/test frequencies required)

• Replace step motor with another having finer step precision

• Replace Test PC with newer equipment

• Develop rigorous RC chamber test procedures for JSC

• Test something

MY FUTURE

ACKNOWLEDGEMENTS AND DEEPEST THANKS

• Dr. Scully

• Xiang Ni

• Rick Deppisch

• Isreal Vences

• Wayne Cope

• Denise Romero

• Dr. Norgard

• Chuck Roberts, Victor Murray, Dan Tran

• Missy Mathias