Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 244)

Model 9110TH NOx Analyzer Troubleshooting & Repair
Teledyne Analytical Instruments 224
 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., 0.448 ppm NO and 0.45 ppm 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 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 5.2.5 for more information on this feature.
7.4. 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.
7.4.1. 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 Section.
Another possibility of excessive signal noise may be the preamplifier board, the high
voltage power supply and/or the PMT detector itself. Contact the factory on trouble-
shooting these components.
7.4.2. SLOW RESPONSE
If the analyzer starts responding too slow to any changes in sample, zero or span gas,
check for the following:
 Dirty or plugged sample filter or sample lines.
 Sample inlet line is too long.
 Leaking NO/NO
X
valve. Carry out a leak check.
 Dirty or plugged critical flow orifices. Check flows, pressures and, if
necessary, change orifices (Section 6.4.6).