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APPENDIX C
Symptom: Dew point reading -100 or +473
Cause
Diagnosis
Resolution
Cause
Diagnosis
Resolution Contact Michell Instruments' Service department
Cause
Diagnosis
Resolution Contact Michell Instruments' Service department
Symptom: Dew-point reading shows ambient or fi xed temperature
Cause
Diagnosis
Resolution
Cause
Diagnosis
Resolution Contact Michell Instruments' Service department
Cause
Diagnosis
Resolution Contact Michell Instruments' Service department
Cause
Diagnosis
Resolution Contact Michell Instruments' Service department
Cause
Resolution Contact Michell Instruments' Service department
42
Sensor cable not connected or damaged
Try another sensor cable
Ensure continuity of sensor cable conductors i.e. Pin A – Pin A continuity
Ensure sensor cable connections are sound
Source replacement sensor cable from local Michell Instruments representative
Sensor PRT damaged – open or short circuit
Try another sensor
Measure resistance between sensor pins A & B. Should be ~108 Ω @ 21°C
Instrument hardware fault
First try the troubleshooting steps listed above
Sensor cable not connected or damaged
Try another sensor cable
Ensure continuity of sensor cable conductors i.e. Pin A – Pin A continuity
Ensure sensor cable connections are sound
Source replacement sensor cable from local Michell Instruments representative
Heating transistor on instrument damaged
Run a DCC cycle, and run a MAXCOOL for a short period
If temperature does not increase during DCC but does decrease during
MAXCOOL then heating transistor on instrument damaged
Cooling transistor on instrument damaged
Run a DCC cycle, and run a MAXCOOL for a short period
If temperature increases during DCC but does not decrease during MAXCOOL
then cooling transistor on instrument damaged
Heat pump damaged
Try heating/cooling tests above
Try a known working sensor with the instrument
Check heat pump resistance between pins J and K on sensor connector,
nominal 4 - 8 Ω
Instrument hardware fault
Optidew Series User's Manual
97430 Issue 2, March 2017
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