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No response – Teledyne 9110EH - Nitrogen Oxides Analyzer User Manual

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Model 9110EH Instruction Manual Troubleshooting & Repair

high, positive values. The M9110EH has a built-in Auto-zero function, which should take

care of most of these deviations from zero, but may yield a small, residual, negative
value. If larger, negative values persist continuously, check if the Auto-zero function

was accidentally turned off using the remote variables in Appendix A-2. In this case,
the sensitivity of the analyzer may be drifting negative.

• A corruption of the Auto-zero filter may also cause negative concentrations. If a

short, high noise value was detected during the AutoZero cycle, that higher reading
will alter the Auto-zero filter value. As the value of the Auto-zero filter is subtracted

from the current PMT response, it will produce a negative concentration reading.
High AutoZero readings can be caused by

• a leaking or stuck AutoZero valve (replace the valve),
• by an electronic fault in the preamplifier causing it to have a voltage on the PMT

output pin during the AutoZero cycle (replace the preamplifier),

• by a reaction cell contamination causing high background (>40 mV) PMT

readings (clean the reaction cell),

• by a broken PMT temperature control circuit, allowing high zero offset (repair the

faulty PMT cooler). After fixing the cause of a high Auto-zero filter reading, the

M200E will take 15 minutes for the filter to clear itself, or

• by an exhausted chemical in the ozone scrubber cartridge (Section 9.3.3).

• Mis-calibration is the most likely explanation for negative concentration values. If the

zero air contained some NO or NO

2

gas (contaminated zero air or a worn-out zero air

scrubber) and the analyzer was calibrated to that concentration as “zero”, the
analyzer may report negative values when measuring air that contains little or no

NO

x

. The same problem occurs, if the analyzer was zero-calibrated using zero gas

that is contaminated with ambient air or span gas (cross-port leaks or leaks in
supply tubing or user not waiting long enough to flush pneumatic systems).

• If the response offset test functions for NO (NO OFFS) or NO

X

(NOX OFFS) are

greater than 150 mV, a reaction cell contamination is indicated. Clean the reaction

cell according to Section 9.3.9.

11.3.2. No Response

If the instrument shows no response (display value is near zero) even though sample gas is
supplied properly and the instrument seems to perform correctly.

• Check if the ozone generator is turned on. Usually, the analyzer issues a warning

whenever the ozone generator is turned off. Go to SETUP-MORE-DIAG-ENTR, then
scroll to the OZONE GEN OVERRIDE and see if it shows ON. If it shows OFF, turn

it ON and EXIT the DIAG menu. If this is done and the ozone flow is correct, the
analyzer should be properly supplied with ozone unless the generator itself is

broken. A more detailed description of the ozone generator subsystem checks are in
Section 11.5.167.

• Confirm the lack of response by supplying NO or NO

2

span gas of about 80% of the

range value to the analyzer.

• Check the sample flow and ozone flow rates for proper values.
• Check for disconnected cables to the sensor module.
• Carry out an electrical test with the ELECTRICAL TEST procedure in the diagnostics

menu, see Section 6.7.6. If this test produces a concentration reading, the
analyzer’s electronic signal path is correct.

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