Detcon TP-700 - Manual (Page 34)

Model TP-700
TP-700 Instruction Manual Rev. 3.5 Page 30 of 38
6. Troubleshooting Guide
Refer to the list of Failsafe Diagnostic features listed in Section 3.6.2 for additional reference in
troubleshooting activities. Listed below are some typical trouble conditions and their probable cause and
resolution path.
Figure 13 Sensor PCB
Open Heater
Probable Cause: Plug-in sensor has failed
 Remove plug-in H
2
S sensor and verify resistance between PIN 2 and PIN 3 (Shown in Figure 13)
using an ohmmeter. At room temperature, the heater film’s normal reading should range between 65
and 95 ohms.
 Replace the plug-in H
2
S sensor if open circuit or significantly out-of range readings are found.
Open Sensor
Probable Cause: Plug-in sensor has failed

Remove plug-in H2S sensor cell and verify resistance between PIN 6 and PIN 7 (Shown in Figure 13)
using an ohmmeter. At room temperature, the sensor film’s normal reading range should be 10-100 k-
ohms. For sensors with an “X” in the serial number, the normal reading range should be 75 k-ohms to
2 meg-ohms. Failure would be open circuit.
 Replace the plug-in H
2
S sensor cell if an open circuit found.
AutoSpan Calibration Faults – (Range, Stability and Clearing)
To clear any AutoSpan Calibration fault, the AutoSpan process must be completed successfully (Section3.4).
Range Fault
Probable Causes: Failed Sensor, Cal Gas not applied or not applied at appropriate time, problems w/ cal gas
and delivery, no Humidifying Tube used, failure to properly desiccant packet the sensor cell during extended
power-off periods.
 Check Heater Power Setting (should be 235 +/- 5mW at 25ºC ambient temperature).
 Verify use of span gas Humidifying Tube.
 If using Splashguard with Integral Cal Port, must use Calibration Wind Guard or air movement can
compromise span gas delivery.
 Check validity of span gas using H
2
S pull tube or other means (check MFG date on cal gas cylinder).
 Check for obstructions through stainless steel flame arrestor (including being wet, blocked, or
corroded).