Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 221)

Model 9110EH Instruction Manual Troubleshooting & Repair
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.
11.4.2. 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 9.3.10).
• 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.
11.4.3. 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 span gas reading (e.g., 800-900 mV at 400
ppb NO) 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).
Note 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
M9110EH Rev 0 207