COSA Xentaur Xentaur HDT - Manual (Page 18)

Section 2: Sensor and Sampling Techniques
page 11
Troubleshooting unexpected readings (continued from previous page)
Symptom Diagnostic/Remedy
Reading is not
changing
Condensation will occur if the temperature of the sample system, at any point is below
(colder) the dewpoint temperature of the sample gas. Once having formed, the sample
reaching the sensor will have a dewpoint equal to the temperature of the condensation,
regardless of the dewpoint 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” (3mm) o.d. sample pipe.
See below re: sample pipe material, also see section 2.3
Dry Reading return sensor for full calibration to your representative.
Wet Reading
Cure the leak, or replace unsuitable pipe with copper or stainless steel. Flexible con-
nections should be made with PTFE pipe. NEVER use rubber or plastic pipe.
This type of indicator reads about 10°C dry at about -50°C dewpoint due to tempera-
ture gradients within the device. The error increases at drier levels.
Dry the sensor, install sensor in either a known dry gas stream i.e. instrument quality
air or dry nitrogen, or place sensor in a dry can or bottle of desiccant and seal the con-
tainer from outside air (the shipping container is designed for this purpose)
Remove (unscrew) sensor, if the current does not change even momentarily, then the
problem is with the instrument, otherwise the problem may be with the sensor.
Check sensor connection or replace sensor.