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EPA Precursor Gas Training Workshop
NCore Calibration IssuesMeeting the new QC Requirements
Lewis Weinstock and Dennis Mikel EPA Office of Air Quality, Planning
and Standards
EPA Precursor Gas Training Workshop
• Overview of NCore technical requirements
• Mass Flow Controllers (MFC) Calibrators
• Compressed Gas Cylinders
• Zero Air Generators
• Summary
Key Topics
EPA Precursor Gas Training Workshop
NCore Calibration Challenges
• Operating analyzers on lower ranges where ambient data are more affected by instrument drift and interferences– Old CO range 0 – 50 ppm for NAAQS compliance
– Typical NCore CO range 0 – 5 ppm or even lower
• More frequent QC checks advised so calibration automation is important
• Integration of data systems and calibrators important for QC validation and timely reporting of problems
• Calibration standard certification periods are shorter for lower concentration standards
• Zero air purity is more critical than ever• Reviewing your calibrator capabilities and potentially upgrading
hardware may be the most important part of designing and implementing a successful NCore gas monitoring system
EPA Precursor Gas Training Workshop
• QC Checks (Precision): – Required (40 CFR 58 Appendix A)– Minimum: Once every two weeks – daily is recommended– Daily Level 1 Zero and Spans recommended
• Multi-point calibrations: – Quarterly (according to TAD) or if drift is an ongoing issue– Draft MQO Table - 1 in 6 months, upon instrument startup,
repair, or exceeded drift tolerance
• MDL Tests (New requirement): – Annually or after major analyzer repair
• Consider entire system when troubleshooting QC problems – zero air or calibrator issues may be the cause– Don’t just recalibrate repeatedly when analyzer drift and/or
linearity problems are indicated
NCore Calibration and QC Check Requirements
EPA Precursor Gas Training Workshop
Item CO SO2 NOy
Full Scale Range 0 to 5000 ppb 0 to 100 ppb 0 to 200 ppb
Cylinderconcentration
200 – 300 ppm 10 - 15 ppm 10 – 30 ppm
Calibration ranges
Zero(action tolerance)
+ 40 ppb + 0.100 ppb + 0.050 ppb
Level I Span(action tolerance)
4500 ppb + 10% 90 ppb + 10% 180 ppb + 10%
Mid Point Span 2500 ppb 50 ppb 100 ppb
Precision Level 250 - 500 ppb 5 - 10 ppb 20 - 40 ppb
MeasurementUncertainty Goal
10%upper 90 percent confidence
limit for CV
10%upper 90 percent confidence
limit for CV
10%upper 90 percent confidence
limit for CV
Calibration and QC Check Concentrations** For a typical urban NCore station
EPA Precursor Gas Training Workshop
Example QC Control Chart
CO TEI - Precision Drift - Burdens Creek (500 ppb)
-20.0%
-15.0%
-10.0%
-5.0%
0.0%
5.0%
10.0%
15.0%
20.0%
EPA Precursor Gas Training Workshop
Method Detection Limit Test(How do you run it?)
• Use a concentration of 2.5 to 5 times the instrument signal/noise• Run zero gas through analyzer• Dilute the calibration gas to estimated concentration level and collect
readings for a predetermined length of time: – Suggested: 20-25 1 minute observations, repeated 7 times over the
course of 5 -14 days. Average the concentration from these readings.
• Calculate the MDL as:
stMDL n 1,01.
Where represents the 99th quantile of a Student’s t distribution with (n-1) degrees of freedom and n represents the number of replicate measurements and s is the standard deviation.
1,01. nt
EPA Precursor Gas Training Workshop
Method Detection Limit Test
• Confirms that a trace-level analyzer is really performing as a trace level– Perform as part of acceptance testing– Annually as part of regular QA program– After a major repair such as detector replacement
• Operational challenges– Need to accurately and repeatedly generate a very small
concentration– Will need dedicated low-level gas cylinder standards in the 1 ppm
range for NO and SO2, and 10 ppm range for CO• Agencies can share cylinders• Possible development of cylinder “bank”
– Dilution challenges capacity of zero air scrubbing system at high flows (~ 20 LPM)
EPA Precursor Gas Training Workshop
Example Method Detection Limit Test
CO Analyzers MDL Test 2/4(Red=T-CO, Blue=A-CO)
-50
-30
-10
10
30
50
70
90
110
130
150
11:3
0
11:4
0
11:5
0
12:0
0
12:1
0
12:2
0
12:3
0
12:4
0
12:5
0
13:0
0
13:1
0
13:2
0
13:3
0
13:4
0
13:5
0
14:0
0
14:1
0
14:2
0
14:3
0
14:4
0
14:5
0
15:0
0
15:1
0
15:2
0
15:3
0
15:4
0
stMDL n 1,01.
API CO MDL TESTS4-Feb 83.315-Feb 87.446-Feb 76.677-Feb 77.228-Feb 75.059-Feb 76.59
10-Feb 73.8111-Feb 75.6612-Feb 67.0313-Feb 80.2914-Feb 78.78
STDev 5.26Avg 77.44
99% 99.50% 99.75% 99.90% 99.95%1 31.82 63.66 127.3 318.3 636.6
2 6.965 9.925 14.09 22.33 31.6
3 4.541 5.841 7.453 10.21 12.92
4 3.747 4.604 5.598 7.173 8.61
5 3.365 4.032 4.773 5.893 6.869
6 3.143 3.707 4.317 5.208 5.959
7 2.998 3.499 4.029 4.785 5.408
8 2.896 3.355 3.833 4.501 5.041
9 2.821 3.25 3.69 4.297 4.781
10 2.764 3.169 3.581 4.144 4.587
MDL = (2.764) * 5.26 = 14.54 ppb
Student's t-distributionFrom Wikipedia, the free encyclopedia
EPA Precursor Gas Training Workshop
Typical Mass Flow Controller (MFC) TheoryCalibrator Diagram
Zero Air MFC
EPA Precursor Gas Training Workshop
Calibrator Critical Specifications
• Gas Flow – 0 to 100 cc/min • Air Flow – 0 – 20 L/min• Multiple Gas ports - optional• Built in traceable ozone
generator • Accuracy +/- 1% Full Scale• Precision +/- 1% Full Scale • Linearity +/- 1% Full Scale
Environics 9100
EPA Precursor Gas Training Workshop
Calibrator Specification Matrix (EPA Research 2006)
Calibrator Gas* Flow
Air*
Flow
Gas input Ports
Ozone
Gen.
Flow Accuracy
Flow
Precision
Linearity
Ecotech 1100
0-500 sccm
0-20 lpm 4 Std. Yes, 0 – 1ppm
+/- 1.0%
Full Scale
+/- 0.15%
Full Scale
0.15%
Full Scale
Environics
9100
0-100 sccm
0-20 lpm 2 Std. Yes, 0.5 – 1.25 ppm
+/- 1.0%
Full Scale
+/- 1.0%
Full Scale
1.0%
Full Scale
Sabio
4010L
0-1000
sccm
0-20 lpm Yes Yes, 0 –
2 ppm
+/- 1.0%
Full Scale
+/- 0.15%
Full Scale
0.5%
Full Scale
Tanabyte
300
0-100 sccm
0-10** lpm
Yes Yes, 0 –
2 ppm
+/- 0.5%
Full Scale
+/- 0.1%
Full Scale
0.5%
Full Scale
Teledyne- API 700E
0-200 sccm
0-20 lpm 4 Std. Yes, 0.1 – 10 ppm
+/- 1.0%
Full Scale
+/- 0.2%
Full Scale
0.5%
Full Scale
Thermo
146C
0-200 sccm
0-20 lpm NA Yes +/- 1.0%
Full Scale
+/- 1.0%
Full Scale
1.5%
Full Scale
* Highest optional ranges. ** Tanabyte offers a 0 – 20 lpm option
EPA Precursor Gas Training Workshop
Calibrator Critical Features
• Option for multiple gas flow controllers to expand dynamic dilution range– Want to stay away from flows less than 10% or greater than
90% of MFC full scale
• Internal calculation of MFC flow response• Programmable scheduled tasks • Remote access and control ready (accept direct
digital commands)• Digital Inputs – controlled by remote access• Digital Outputs – signals to remote device• Capability to directly control solenoids without
external power supplies
EPA Precursor Gas Training Workshop
Calibrator Feature Matrix (EPA Research 2006)
Calibrator Programmable Calibrations
Display Digital Inputs Digital Outputs
Ecotech 1100 Yes, 20 sequences cycled through 5 points
4 line LCD Relay contact closures or TTL logic
8 digital outputs for sequence indication
Environics
9100
Yes, 21 sequences (3/day) through 5 points
LCD Optional RS-232 serial data interface
8 digital outputs for sequence indication
Sabio
4010L
20 timer driven cal routines, user defined sequences on a 7 day calendar
Bright active matrix color display
24 bit Digital Input, TTL logic levels, RS-232
24 bit output,
2 serial ports for communication
Tanabyte
300
Menu operation allows auto or manual calibrations
LCD TTL contact closures allows remote operation
Via RS-232 300 -9600 baud
Transparent pass serial I/0 after programmable pass-code is received
Teledyne- API 700E
Readout and control by front panel
2 line LCD Via RS-232
12 opto-isolated inputs
Via RS-232
12 opto-isolated outputs
Thermo
146C
10 calibration events 4 line LCD RS-232 remote access RS-232 remote access
EPA Precursor Gas Training Workshop
Certifying your Calibrator Flows
• Initial calibration should be provided with purchase – always recheck after delivery
• Certify flow controllers against a NIST traceable flow device (such as a Bios DryCal, Gilibrator or Hastings Bubble Kit or other flow device)
• NIST Traceable flow device should be certified annually (or if you suspect a problem)
• Perform quarterly or semi-annual checks of your MFCs (or until establish trend)
• Calculate observed flow vs set points at STP (25 degrees Celsius and 760 mm Hg)
EPA Precursor Gas Training Workshop
MFC Calibration - Burdens Creek (1-23-2007)Environics 9100 #A50930
ZERO AIR FLOW CONTROLLER MFC1 LAST CERTIFICATION: 8/21/2006L/M (5 REPLICATES PER READING)
POINT# DISPLAY/SET DRYCAL1 DRYCAL2 DRYCAL3 DRYCAL4 DRYCAL5 AVERAGE1 20.0 19.90 19.80 19.82 19.81 19.80 19.8262 18.0 17.58 17.60 17.61 17.58 17.58 17.5903 16.0 15.67 15.68 15.67 15.68 15.67 15.6744 14.0 13.71 13.72 13.74 13.74 13.72 13.7265 12.0 11.82 11.83 11.84 11.83 11.82 11.8286 10.0 9.90 9.91 9.92 9.91 9.91 9.9107 8.0 7.95 7.95 7.94 7.94 7.94 7.9438 6.0 5.98 5.98 5.98 5.98 5.98 5.9809 4.0 4.01 4.01 4.01 4.01 4.00 4.00810 2.0 1.99 2.00 1.99 1.99 2.00 1.99411 1.0 0.976 0.987 0.976 0.981 0.978 0.980
ENVIRONICS 9100 MFC 1 y = 0.9812x + 0.0493
R2 = 0.9999
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
20.00
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
SET FLOW
OB
S F
LO
W
EPA Precursor Gas Training Workshop
MFC Calibration - Burdens Creek (1-23-2007)Environics 9100 #A50930
GAS AIR FLOW CONTROLLER MFC2 LAST CERTIFICATION: 8/21/2006SCCM (5 REPLICATES PER READING EXCEPT LOWEST 3PTs)
POINT# DISPLAY/SET DRYCAL1 DRYCAL2 DRYCAL3 DRYCAL4 DRYCAL5 AVERAGE1 100.0 97.59 97.61 97.41 97.04 97.83 97.4962 90.0 87.65 88.14 87.93 87.94 87.76 87.8843 80.0 76.12 76.58 76.69 76.88 76.35 76.5244 70.0 68.10 67.80 67.72 67.69 68.41 67.9445 60.0 58.86 59.10 59.17 58.67 58.53 58.8666 50.0 49.09 49.07 48.99 49.19 49.12 49.0927 40.0 39.32 39.52 39.45 39.68 39.55 39.5048 30.0 29.29 29.07 28.98 29.10 29.10 29.1089 20.0 19.17 19.10 19.22 19.15 19.00 19.128
10 10.0 9.55 9.72 9.59 9.63 9.43 9.58211 5.0 4.47 4.59 4.45 4.49 4.62 4.525
ENVIRONICS 9100 MFC 2 y = 0.9741x - 0.0883
R2 = 0.9997
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
SET FLOW
OB
S F
LO
W
EPA Precursor Gas Training Workshop
Compressed Gas Cylinders - Features
• Come in variety of sizes (size 50 or 150)• Recommend using Aluminum cylinders• Get EPA Protocol certification from experienced vendors
– http://www.epa.gov/appcdwww/pubs/600r97121/600r97121.htm– Note: certification periods can be shorter than expected for low
concentration cylinders (next slide)• Use Stainless Steel regulators and cylinder valves• Use Stainless steel or Teflon lines from Regulator to
MFC (Teflon recommended)• Recommended Cylinder Concentrations for the NCore
Sites: – SO2: 10 – 15 ppm– NO: 10 – 30 ppm– CO: 200 – 300 ppm – Oxygen free - Balance Nitrogen
EPA Precursor Gas Training Workshop
Zero Air Source - Issues
• The air system should be able to provide clean air below the stated Lower Detection Limits (LDL) of the instruments you are operating at maximum required flow rates (up to 20 l/min)– NO: 50 ppt– SO2: 100 ppt – CO: 40 ppb
• Check the specifications before you purchase
• Regularly maintain/replace scrubbing materials TEI Model 111
T_API Model 701
EPA Precursor Gas Training Workshop
Zero Air Generation - Issues
Ultra Pure Cylinder Air vs. Zero Air Generators
Trade off:
Quantity Used vs. Costs for cylinders– High flow rates – Humidity issues– Purity of air generated– Use Ultra Pure Cylinder air to verify Generator purity
(recommended)
EPA Precursor Gas Training Workshop
Summary
• QC Checks and calibrations are required for NCore Monitoring Stations
• The MFC systems available today are compatible with the PG instruments and support a high degree of automation
• Calibration systems should be regularly flow certified with NIST-traceable devices
• Lower concentrations cylinders are required since PG instruments have lower ranges and levels of detection
• Gas cylinders should be certified – EPA Protocol• Zero air generators should be able to “scrub”
below the LDLs of the PG instruments