Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 246)

Model 9110TH NOx Analyzer Troubleshooting & Repair
Teledyne Analytical Instruments 226
 A dirty reaction cell can cause high AutoZero values. Clean the reaction
cell according to Section 6.4.5.
 Finally, a high HVPS voltage value may cause excess background noise
and a high AZERO value. The HVPS value changes from analyzer to
analyzer and could show nominal values between 450 and 800 V. Check
the low-level hardware calibration of the preamplifier board and, if
necessary, recalibrate exactly as described in Section 13 in order to
minimize the HVPS.
7.5. SUBSYSTEM CHECKOUT
The preceding sections of this manual discussed a variety of methods for identifying
possible sources of failures or performance problems within the analyzer. In most cases
this included a list of possible causes and, in some cases, quick solutions or at least a
pointer to the appropriate sections describing them. This section describes how to
determine if a certain component or subsystem is actually the cause of the problem being
investigated.
7.5.1. SIMPLE LEAK CHECK USING VACUUM AND PUMP
Leaks are the most common cause of analyzer malfunction; This section presents a
simple leak check, whereas Section 7.5.2 details a more thorough procedure. The
method described here is easy, fast and detects, but does not locate, most leaks. It also
verifies the sample pump condition.
 Turn the analyzer ON, and allow at least 30 minutes for flows to stabilize.
 Cap the sample inlet port (cap must be wrench-tight).
 After several minutes, when the pressures have stabilized, the SAMP
(sample pressure) and the RCEL (vacuum pressure) readings.
 If both readings are equal to within 10% and less than 10 in-Hg-A, the
instrument is free of large leaks. It is still possible that the instrument has
minor leaks.
 If both readings are < 10 in-Hg-A, the pump is in good condition. A new
pump will create a pressure reading of about 4 in-Hg-A (at sea level).
7.5.2. DETAILED LEAK CHECK USING PRESSURE
If a leak cannot be located by the above procedure, obtain a leak checker similar to TAI
part number 01960, which contains a small pump, shut-off valve, and pressure gauge to
create both over-pressure and vacuum. Alternatively, a tank of pressurized gas, with the
two stage regulator adjusted to ≤ 15 psi, a shutoff valve and pressure gauge may be used.
Note Once tube fittings have been wetted with soap solution under a
pressurized system, do not apply or re-apply vacuum as this will cause
soap solution to be sucked into the instrument, contaminating inside