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Calibration Procedures Teledyne API – Model T300/T300M CO Analyzer
198
9.1.1.1. ZERO AIR
Zero air or zero calibration gas is defined as a gas that is similar in chemical
composition to the measured medium but without the gas to be measured by the
analyzer.
For the T300/T300M zero air should contain less than 25 ppb of CO and other major
interfering gases such as CO and Water Vapor. It should have a dew point of -5C or
less.
If your application is not a measurement in ambient air, the zero calibration gas should
be matched to the composition of the gas being measured.
Pure nitrogen (N
2
) can be used as a zero gas for applications where CO is
measured in nitrogen.
If your analyzer is equipped with an external zero air scrubber option, it is capable of
creating zero air from ambient air.
For analyzers without the zero air scrubber, a zero air generator such as the Teledyne
API’s T701 can be used. Please visit the company website for more information.
9.1.1.2. SPAN GAS
Span Gas is a gas specifi
cally mixed to match the chemical composition of the type of
gas being measured at near full scale of the desired measurement range. It is
recommended that the span gas used have a concentration equal to 80-90% of the full
measurement range.
If Span Gas is sourced directly from a calibrated, pressurized tank, the gas mixture
should be CO mixed with Zero Air or N
2
at the required ratio.
For oxygen measurements using the optional O
2
sensor, we recommend a reference gas
of 21% O
2
in N
2
.
For quick checks, ambient air can be used at an assumed concentration of 20.8%.
Generally, O
2
concentration in dry, ambient air varies by less than 1%.
9.1.1.3. CALIBRATION GAS STANDARDS AND TRACEABILITY
All equipment used to produce calibration gases should be verified against standards of
the National Institute for Standards and Technology (NIST). To ensure NIST
traceability, we recommend to acquire cylinders of working gas that are certified to be
traceable to NIST Standard Reference Materials (SRM). These are available from a
variety of commercial sources.
Table 9-1: NIST-SRMs Available for Traceability of CO Calibration Gases
NIST-SRM Type Nominal Concentration
680b 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
2659a1 O
2
in N
2
21% by weight
2626a CO
2
in N
2
4% by weight
27452 CO
2
in N
2
16% by weight
1
Used to calibrate optional O
2
sensor.
2
Used to calibrate optional CO
2
sensor.
Note
It is generally a good idea to use 80% of the reporting range for that channel for
the span point calibration.
For instance, if the reporting range of the instrument is set for 50.0 PPM, the
proper span gas would be 40.0 PPM.
06864B DCN6314