083730300A DCN8101 Calibration 91
4.1.2 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 -5°C 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.
4.1.3 CALIBRATION (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 and should be
certified traceable to NIST Standard Reference Materiald (SRM). 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 bottle, use the exact
concentration value printed on the bottle.
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%.
4.1.4 INTERFERENTS
It should be noted that the gas filter correlation method for detecting CO is subject to
interference from a number of other gases that absorb IR in a similar fashion to CO.
Most notable of these are water vapor, CO
2
, N
2
O (nitrous oxide) and CH
4
(methane). The
T300/T300M has been successfully tested for its ability to reject interference from of
these sources, however high concentrations of these gases can interfere with the
instrument’s ability to make low-level CO measurements.
For a more detailed discussion of this topic, see Section 6.1.2.4.
4.1.5 DILUTION RATIO OPTION SOFTWARE SET UP
If your application involves diluting the sample gas before it enters the analyzer, and the
Dilution Ratio Option is enabled:
1. Set the appropriate units of measure (Setup>Vars>User Units).
2. Select the reporting range mode (Setup>Vars>Range Mode [Single or Dual]).
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