083730300A DCN8101 Getting Started 39
2.3.2.1 IMPORTANT INFORMATION ABOUT CALIBRATION GASES
Zero air and span gas are required for accurate calibration.
ZERO AIR
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 Teledyne API Model T701 can be used.
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 T300 or T300M 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.
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 2-6 lists specific NIST-SRM reference numbers for
various concentrations of CO.
Table 2-6. 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
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.
To Next Page
Loading...