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Getting Started Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 43
3.4.1.2. Span Gas
Span gas is a gas specifically mixed to match the chemical composition of the type of gas being
measured at near full scale of the desired measurement range. In the case of CO measurements made
with the GFC 7001E/EM Analyzer, it is recommended that you use a span gas with a CO concentration
equal to 80-90% of the measurement range for your application.
EXAMPLE: If the application is to measure between 0 ppm and 500 ppb, an appropriate span gas
concentration would be 400-450 ppb CO in N2.
Some applications, such as EPA monitoring, require a multipoint calibration procedure where span gases
of different concentrations are needed. We recommend using a bottle of calibrated CO gas of higher
concentration in conjunction with a gas dilution calibrator such as a Teledyne’s M700. This type of
calibrator precisely mixes a high concentration gas with zero air (both supplied externally) to accurately
produce span gas of the correct concentration. Linearity profiles can be automated with this model and
run unattended over night.
Cylinders of calibrated CO gas traceable to NIST-Standard Reference Material specifications (also
referred to as SRMs or EPA protocol calibration gases) are commercially available. Table 3-7 lists specific
NIST-SRM reference numbers for various concentrations of CO.
Table 3-7: NIST-SRM's Available for Traceability of CO Calibration Gases
NIST-SRM TYPE
NOMINAL
CONCENTRATION
1680b CO in N
2
500 ppm
1681b CO in N
2
1000 ppm
2613a CO in Zero Air 20 ppm
2614a CO in Zero Air 45 ppm
2659a
1
O
2
in N
2
21% by weight
2626a CO
2
in N
2
4% by weight
2745* CO
2
in N
2
16% by weight
1
Used to calibrate optional O
2
sensor.
2
Used to calibrate optional CO
2
sensor.