Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 71)

Getting StartedTeledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 71
3.3.2.10. CALIBRATION GASES
Zero air and span gas are required for accurate calibration.
Z ERO A IR
Zero air is a gas that is similar in chemical composition to the earth’s atmosphere but
scrubbed of all components that might affect the analyzer’s readings, in this case CO
and water vapor. If your analyzer is equipped with an Internal Zero Span (IZS) or an
external zero air scrubber option, it is capable of creating zero air.
If the analyzer is NOT equipped with the optional CO
2
sensor, zero air should be
scrubbed of CO
2
as well, as this gas can also have an interfering effect on CO
measurements.
For analyzers without an IZS or external zero air scrubber option, a zero air generator
such as the TAI Model T701 can be used.
S PAN G AS
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 GFC7001T or GFC7001TM 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 N
2
.
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 3-12 lists specific NIST-SRM reference numbers for
various concentrations of CO.
Table 3-12: 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.
S PAN G AS FOR M ULTIPOINT C ALIBRATION
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 TAI’s T700. This type of calibrator precisely mixes a high concentration gas