Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 245)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 225
 Wrong materials in contact with sample - use glass, stainless steel or Teflon
materials only. Porous materials, in particular, will cause memory effects
and slow changes in response.
 Dirty reaction cell. Clean the reaction cell.
 Insufficient time allowed for purging of lines upstream of the analyzer.
Wait until stability is low.
 Insufficient time allowed for NO or NO
2
calibration gas source to become
stable. Wait until stability is low.
 NO
2
converter temperature is too low. Check for proper temperature.
7.4.3. AUTO ZERO WARNINGS
Auto-zero warnings occur if the signal measured during an auto-zero cycle is lower than
–20 mV or higher than 200 mV. The Auto-Zero warning displays the value of the auto-
zero reading when the warning occurs.
 If this value is higher than 150 mV, check that the auto-zero valve is
operating properly. To do so, use the SIGNAL I/O functions in the DIAG
menu to toggle the valve on and off. Listen if the valve is switching, see if
the respective LED on the relay board is indicating functionality. Scroll the
TST functions until PMT is displayed and observe the PMT value change
between the two valve states.
 If the valve is operating properly, you should be able to hear it switch (once
a minute under normal operation or when manually activated from the
SIGNAL I/O menu), the PMT value should drop from its nominal reading
for span gas level measurements to less than 150 mV and the LED on the
relay board should light up when the valve is activated. If the PMT value
drops significantly but not to less than 150 mV, the valve is probably
leaking across its ports. In this case, replace the valve. If the PMT value
does not change at all, the valve is probably not switching at all. Check the
power supply to the valve (12 V to the valve should turn on and off when
measured with a voltmeter).
 that it takes only a small leak across the ports of the valve to show
excessive auto-zero values when supplying high concentrations of span gas.
 Another reason for high (although not necessarily out-of-range) values for
AutoZero could be the ozone air filter cartridge, if its contents has been
exhausted and needs to be replaced. This cartridge filters chemicals that can
cause chemiluminescence and, if saturated, these chemicals can break
through to the reaction cell, causing an erroneously high AutoZero value
(background noise).