Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 262)

Model 9110TH NOx Analyzer Troubleshooting & Repair
Teledyne Analytical Instruments 242
 Temperature is reported properly but heater does not heat to full
temperature. In this case, the heater is either disconnected or broken or the
power relay is broken.
 Disconnect the heater cable coming from the relay board and measure the
resistance between any two of the three heater leads with a multi-meter. The
resistance between A and B should be about 1000 Ω and that between A and C
should be the same as between B and C, about 500 Ω each. If any of these
resistances is near zero or without continuity, the heater is broken.
 Temperature reports zero or overload (near 500° C). This indicates a
disconnected or failing thermocouple or a failure of the thermocouple
circuit.
 First, check that the thermocouple is connected properly and the wire does not
show signs of a broken or kinked pathway. If it appears to be properly connected,
disconnect the yellow thermocouple plug (marked K) from the relay board and
measure the voltage (not resistance) between the two leads with a multi-meter
capable of measuring in the low mV range. The voltage should be about 12 mV
(ignore the sign) at 315° C and about 0 mV at room temperature.
 Measure the continuity with an Ohm-meter. It should read close to zero Ω. If
the thermocouple does not have continuity, it is broken. If it reads zero voltage at
elevated temperatures, it is broken. To test the thermocouple at room temperature,
heat up the converter can (e.g., with a heat gun) and see if the voltage across the
thermocouple leads changes. If the thermocouple is working properly, the
electronic circuit is broken. In both cases, consult the factory.
If the converter appears to have performance problems (conversion efficiency is outside
of allowed range of 96-102%), check the following:
 Conversion efficiency setting in the CAL menu. If this value is different
from 1.000, this correction needs to be considered. Section 5.2.5 describes
this parameter in detail.
 Accuracy of NO2 source (gas tank standard). NO2 gas standards are
typically certified to only ±2% and often change in concentrations over
time. You should get the standard re-certified every year. If you use GPT,
check the accuracy of the ozone source.
 Age of the converter. The NO2 converter has a limited operating life and
may need to be replaced every ~3 years or when necessary (e.g., earlier if
used with continuously high NO2 concentrations). We estimate a lifetime
of about 10000 ppm-hours (a cumulative product of the NO2 concentration
times the exposure time to that concentration). However, this lifetime
heavily depends on many factors such as absolute concentration (temporary
or permanent poisoning of the converter is possible), sample flow rate and
pressure inside the converter, converter temperature, duty cycle etc. This
lifetime is only an estimated reference and not a guaranteed lifetime.
 In some cases with excessive sample moisture, the oxidized molybdenum
metal chips inside the converter cartridge may bake together over time and
restrict air flow through the converter, in which case it needs to be replaced.