AquaXact Issue 1.0
© Servomex Group Limited 2017
21
Sensor
8.2
To troubleshoot unexpected readings from the sensor, identify the unexpected reading
category in the following table, and consider the possible causes and appropriate
diagnostic action and remedy.
Symptom
Possible cause
Reading is not changing
Condensation in sample system
Slow response
1. Water vapor in the system
2. Flow rate too low
3. Sample pipe too large and/or too long
4. Unsuitable sample pipe material
5. Leaks
6. Hygroscopic materials in sample system
Dry reading
Faulty sensor
Wet reading
Leak in system or use of unsuitable pipe.
Comparison of readings with manual cooled-
mirror instrument.
Current loop outside of 4-20mA range 1. Prolonged exposure to wet gas
2. Instrument failure
3. Short circuited sensor
4. Open circuit on sensor
5. Instrument failure
Reading is not changing
Condensation will occur if the temperature of
the sample system, at any point is below
(colder) the dew point temperature of the
sample gas. Once having formed, the sample
reaching the sensor will have a dew point
equal to the temperature of the condensation,
regardless of the dew point of the sample at
the sample point.
Slow Response
It is usually more satisfactory to bleed a
sample gas at atmospheric pressure through
the sensor sampling chamber, and to use 1/8”
(3 mm) o.d. sample pipe.
