Diagnosis and Troubleshooting
9-5
August 2003
Common 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 9-2 below contains some
of the most common measurement problems.
.
Table 9-2: Troubleshooting Guide for Common
Problems
Possible Cause
System
Response
Action
Symptom: Accuracy of moisture sensor is questioned.
Insufficient time for
system to equilibrate
Dew point at sampling
point is different than
the dew point of the
main stream.
Probe reads too
wet during dry
down condi-
tions, or too dry
in wet up con-
ditions.
Probe reads too
wet or too dry.
Change the flow rate. A change in
dew point indicates the sample sys-
tem is not at equilibrium, or there is a
leak. Allow sufficient time for sam-
ple system to equilibrate and mois-
ture reading to become steady. Check
for leaks.
Readings may be correct if the sam-
pling point and main stream do not
run under the same process condi-
tions. The different process condi-
tions cause readings to vary. If
sampling point and main stream con-
ditions 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
Appendix A).
Probe reads too
wet or too dry.
Clean the sensor and the sensor
shield as described in
Aluminum
Oxide Probe Maintenance
on
page A-9 in Appendix A. Then rein-
stall sensor.
