COSA Xentaur Xentaur LPDT - 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 Verify SpanCheck™, or 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.
Display Shows
6$7
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)
Display Shows
6+5
Remove (unscrew) sensor, if the instrument still reads
6+5
the problem is with the
instrument. However, if the instrument reads 231 then check possible cause #2
Remove (unscrew) sensor and note that the meter reading returns to
231
. Use a new
sensor, or apply approximately 20V DC, between the center pin & the filter body of
the sensor, MOMENTARILY with the sensor in a known dry condition. Polarity is not
important, but the contact MUST be very brief or the sensor may be damaged.
Display Shows
Remove (unscrew) the sensor. Short the center contact of the LPDT sensor connection
to the case, if the instrument reads
6+5
the problem is in the sensor, otherwise return
the instrument for service.
231 Check sensor connection or replace sensor.