Chapter 8. Maintenance and Troubleshooting
158 Model PM880 Portable Hygrometer User’s Manual
Symptom: Accuracy of moisture sensor is questioned. (cont.)
Sensor is corroded
(refer to Application of the
Hygrometer).
Probe reads too
wet or too dry.
Return the probe to the factory for
evaluation.
Sensor temperature is
greater than 70°C (158°F).
Probe reads too
dry.
Return the probe to the factory for
evaluation.
Stream particles causing
abrasion.
Probe reads too
wet or too dry
Return the probe to the factory for
evaluation.
Symptom: Screen always reads the wettest (highest) programmed
moisture calibration value while displaying dew/frost point.
Probe is saturated. Liquid
water present on sensor
surface and/or across
electrical connections.
Clean the sensor and the sensor shield as
described in Aluminum Oxide Probe Main-
tenance in Application of the Hygrometer.
Then reinstall sensor.
Shorted circuit on sensor. Run “dry gas” over sensor surface. If high
reading persists, then probe is probably
shorted and should be returned to the
factory for evaluation.
Sensor is contaminated with
conductive particles
(refer to Application of the
Hygrometer).
Clean the sensor and the sensor shield as
described in Aluminum Oxide Probe
Maintenance in Application of the
Hygrometer. Then reinstall sensor.
Improper cable connection. Check the cable connections to both the
probe and the PM880.
Symptom: Screen always reads the driest (lowest) programmed
moisture calibration value while displaying dew/frost point.
Open circuit on sensor.
Non-conductive material is
trapped under the contact
arm of the sensor.
Return probe to factory for evaluation.
Clean the sensor and the sensor shield as
described in Aluminum Oxide Probe
Maintenance in Application of the
Hygrometer. Then reinstall the sensor. If the
low reading persists, return the probe to the
factory for evaluation.
Improper cable connection. Check the cable connections to both the
probe and the PM880.
Table 6: Troubleshooting Guide for Common Problems (cont.)
Possible Cause
System
Response Action
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