Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 232)

Troubleshooting & Repair Model 9110EH Instruction Manual
11.5.15.3. Ozone Flow
Measure the voltage across TP1 and TP3. With proper ozone flow (80 cm³/min at the ozone
dryer inlet), this should be approximately 2.0 ± 0.2 V (this voltage will vary with altitude).
With flow stopped (pump turned off), the voltage should be approximately 0 V. If the
voltage is incorrect, the flow sensor or the board may be faulty. A cross-leak to vacuum
inside the Perma Pure dryer may also cause this flow to increase significantly, and the
voltage will increase accordingly. Also, make sure that the gas flows from P1 to P2 as
labeled on the flow sensor (“high” pressure P1 to “low” pressure P2 or “Port” 1 to “Port” 2).
11.5.16. NO
2
Converter
The NO
2
converter assembly can fail in two ways, an electrical failure of the band heater
and/or the thermocouple control circuit and a performance failure of the converter itself.
1) NO
2
converter heater failures can be divided into two possible problems:
• 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 tempera-
ture, 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.
2) 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 7.1.7 describes this parameter in
detail.
• Accuracy of NO
2
source (GPT or gas tank standard). NO
2
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 NO
2
converter has a limited operating life and may need to
be replaced every ~3 years or when necessary (e.g., earlier if used with continu-
ously high NO
2
concentrations). We estimate a lifetime of about 10000 ppm-hours (a
218 M9110EH Rev 0