GE PM880 - Common Problems

Chapter 8. Maintenance and Troubleshooting
Model PM880 Portable Hygrometer User’s Manual 157
8.12Common Problems
If the PM880 measurement readings seem strange, or they do not make
sense, there may be a problem with the probe or a component of the process
system. Table 6 contains some of the most common measurement problems.
.
Table 6: Troubleshooting Guide for Common Problems
Possible Cause
System
Response Action
Symptom: Accuracy of moisture sensor is questioned.
Insufficient time for system
to equilibrate
Dewpoint at sampling point
is different than the dew-
point of the main stream.
Probe reads too
wet in dry down
conditions, or
too dry in wet
up conditions.
Probe reads too
wet or too dry.
Change the flow rate. A change in dewpoint
indicates the sample system is not at equi-
librium, or there is a leak. Allow sufficient
time for sample system to equilibrate and
moisture reading to become steady. Check
for leaks.
Readings may be correct if the sampling
point and main stream do not run under the
same process conditions. The different
process conditions cause readings to vary. If
sampling point and main stream conditions
are the same, check sample system pipes,
and any pipe between the sample system
and main stream for leaks. Also, check
sample system for adsorbing water
surfaces, such as rubber or plastic tubing,
paper-type filters, or condensed water traps.
Remove or replace contaminating parts
with stainless steel parts.
Sensor or sensor shield
affected by process
contaminants
(refer to Application of the
Hygrometer).
Probe reads too
wet or too dry.
Clean the sensor and the sensor shield as
described in
Aluminum Oxide Probe Maintenance
in Application of the Hygrometer.
Then reinstall the sensor.
Sensor is contaminated with
conductive particles
(refer to Application of the
Hygrometer).
Probe reads
high dewpoint.
Clean the sensor and the sensor shield as
described in Aluminum Oxide Probe Main-
tenance in Application of the Hygrometer.
Then reinstall the sensor.