COSA Xentaur Xentaur LPDT - Manual (Page 15)

LPDT User’s Manual
page 8
It is generally recommended to measure at ambient pressure
for the following reasons:
•
The readings will not be affected by variations in line
pressure.
• The risk of exposing the sensor to liquid water is signif-
icantly reduced.
• ppm readings are computed for a pressure of one atmo-
sphere (1 bar); and have to be corrected using software
in the instrument, or a pressure nomograph, or calcula-
tor if the sensor is measuring at different pressures.
If readings at line pressure are necessary, it is recommended
to measure at ambient pressure and to use the instrument’s
pressure compensation feature to calculate the dewpoint at
line pressure. See appendix F.
Please make sure that:
•
The sample is taken from the upper surface of the main
gas line. This avoids problems with contamination. The
sample should be taken away from pipe line walls where
flow rates may be low, and dewpoint changes may lag.
• For dewpoints dryer than -40°F, use stainless steel tub-
ing only. Copper tubing is acceptable for dewpoints wet-
ter than -40°F. Do not use plastic, rubber or tygon tubing
under any circumstances, as measurements would be
incorrect and/or response time slow due to water reten-
tion inside these materials.
• Try to run pipes to the sensor upwards, so that contami-
nants tend to fall back into the main line.
• Keep the length of the sample line to the sensor as short
as possible.
• Use small diameter pipes (1/4” or 1/8” OD).
• Use sufficient flow rates (e.g. 1 l/min with 6 feet of 1/8”
piping is adequate). The flow rate will influence the sys-
tems’ response time.