Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 220)

Troubleshooting & Repair Model 9110EH Instruction Manual
between high concentrations span gases and the dilution system, oxygen from
ambient air can diffuse into the line and react with NO to form NO
2
. This reaction is
dependent on NO concentration and accelerates with increasing NO concentration,
hence, affects linearity only at high NO levels. Using stainless steel for long span gas
supply lines avoids this problem.
11.3.7. Discrepancy Between Analog Output and Display
If the concentration reported through the analog outputs does not agree with the value
reported on the front panel, you may need to re-calibrate the analog outputs. This becomes
more likely when using a low concentration or low analog output range. Analog outputs
running at 0.1 V full scale should always be calibrated manually. See Section 6.7.3 for a
detailed description of this procedure.
11.3.8. Discrepancy between NO and NO
X
slopes
If the slopes for NO and NO
X
are significantly different after software calibration (more than
1%), consider the following two problems
• NO
2
impurities in the NO calibration gas. NO gases often exhibit NO
2
on the order of
1-2% of the NO value. This will cause differences in the calibration slopes. If the NO
2
impurity in NO is known, it can easily be accounted for by setting the expected
values for NO and NO
2
accordingly to different values, e.g., 448 ppb NO and 450 ppb
NO
X
. This problem is worse if NO gas is stored in a cylinder with balance air instead
of balance gas nitrogen or large amounts of nitrous oxide (N
2
O). The oxygen in the
air slowly reacts with NO to yield NO
2
, increasing over time.
• The expected concentrations for NO and NO
X
in the calibration menu are set to
different values. If a gas with 100% pure NO is used, this would cause a bias. See
Section 7.2.2 on how to set expected concentration values.
• The converter efficiency parameter has been set to a value not equal to 1.000 even
though the conversion efficiency is 1.0. The actual conversion efficiency needs to
match the parameter set in the CAL menu. See Section 7.1.7 for more information
on this feature.
An instrument calibration with the IZS option (and expected concentrations set to the same
amount) will always yield identical slopes for NO and NO
X
, as the instrument measures only
NO
X
and assumes NO to be the same (with NO
2
being zero).
11.4. Other Performance Problems
Dynamic problems (i.e. problems which only manifest themselves when the analyzer is
monitoring sample gas) can be the most difficult and time consuming to isolate and resolve.
The following section provides an itemized list of the most common dynamic problems with
recommended troubleshooting checks and corrective actions.
11.4.1. Excessive noise
Excessive noise levels under normal operation usually indicate leaks in the sample supply or
the analyzer itself. Make sure that the sample or span gas supply is leak-free and carry out
a detailed leak check as described earlier in this chapter.
206 M9110EH Rev 0