Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 29)

Model 9110E Instruction Manual Getting Started
M9110E Rev B 15
For example, if the measurement is NO
X
in ambient air between 0 and 500 ppb, an
appropriate span gas would be NO in air at 400 ppb NO concentration (80% of maximum
range). Even though NO gas in nitrogen could be used as a span gas, the matrix of the
balance gas is different and may cause interference problems or yield incorrect calibrations.
The same applies to gases that contain high concentrations of other compounds (for
example, CO
2
or H
2
O). The span gas should match all concentrations of all gases of the
measured medium as closely as possible.
Cylinders of calibrated NO gas traceable to NIST-standard reference materials specifications
(also referred to as EPA protocol calibration gases) are commercially available.
Some applications, such as EPA monitoring, require a multipoint calibration where span
gases of different concentrations are needed. We recommend using an NO gas of higher
concentration combined with a gas dilution calibrator such as a TAI Model 700. This type of
calibrator mixes a high concentration gas with zero air (both supplied externally) to
accurately produce span gas of the desired concentration. Linearity profiles can be
automated with this model and run unattended overnight. The dynamic range of the M700
is about 0.1 to 0.001 times the original span concentration.
If a dynamic dilution system such as the TAI model 700 is used to dilute high concentration
gas standards to low, ambient concentrations, ensure that the NO concentration of the
reference gas matches the dilution range of the calibrator. Choose the NO gas concentration
such that the dynamic dilution system operates in its mid-range and not at the extremes of
its dilution capabilities. For example, a dilution calibrator with 10-10000 dilution ratio will
not be able to accurately dilute a 5000 ppm NO gas to a final concentration of 500 ppb, as
this would operate at the very extreme dilution setting. A 100 ppm NO gas in nitrogen is
much more suitable to calibrate the M9110E analyzer (dilution ratio of 222, in the mid-
range of the system’s capabilities).
3.3.2. Zero Gas Defined
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, in this case NO
and NO
2
. If your analyzer is equipped with an IZS or external zero air scrubber option, it is
capable of creating zero air from ambient air. However, if your application is not a
measurement in ambient air, the zero calibration gas should be matched to the matrix of
the measured medium. Pure nitrogen could be used as a zero gas for applications where
NO
X
is measured in nitrogen.
For analyzers without zero air options, a zero air generator such as the TAI Model 701 can
be used. Please visit the company website for more information.
If your analyzer is equiped with either the zero/span valve option (Option 50) or the
internal zero/span option (Option 51), the pneumatic connections should be made as shown
in Figure 3-6 (see also Appendix D for detailed diagram).