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HygroPort I.S. User’s Manual
6.1 General Operational Guidelines
General guidelines to be followed when setting-up a sampling system are as follows:
• Insure that the sample is representative of the gas under test
To insure that the sample is representative of the process being monitored, the
sample point should be as close to the critical measurement point as possible.
Also, never sample from the bottom of a pipe where entrained liquids may be
drawn into the instrument’s sample input line.
• Minimize the “dead space” in sample lines
Dead space in sample lines causes moisture entrapment points, increased system
response times or measurement errors as the trapped moisture is released into
the passing sample gas, producing an increase in partial vapor pressure.
Avoid the use of too many fittings, in-line couplings or other unnecessary
tubing. Sample tubing should, ideally, be specially designed for each
application rather than adapted from that previously installed for another
application. Dead space in sample lines increases response time by holding
water molecules which are more slowly released to the passing gas sample.
• Remove any particulate matter or oil from the gas sample
Particulate matter can damage the sensors. If particulate matter, such as
degraded desiccant, pipe scale and rust are likely to be present in the sample gas,
use a particulate in-line filter. Kahn Instruments’ Technical Sales Department
can to provide advice on appropriate methods of filtration.
• Use high quality sample tube fittings
The sample tubing must be capable of withstanding the operating pressure
of the sample line. Wherever possible, always use stainless steel tubing and
fittings. This is particularly important at low dewpoints since other materials, e.g.
nylon, have hygroscopic characteristics and adsorb moisture on the tube walls,
giving rise to slower measurement response and, under certain circumstances,
false dewpoints. For temporary applications, or where stainless steel tubing
is not practical, use high quality, thick-walled PTFE tubing, which exhibits
similar qualities to stainless steel.
In order to minimize response time, always use the shortest run of tubing
and the smallest diameter possible. Take care not to induce pressure
differentials by aiming for too high a fl low rate through too small a diameter.
Kahn Instruments supplies a range of precision pressure fittings suitable for use
with the HygroPort I.S. instrument. Contact Kahn Instruments for details of the
items available.
Issue 6, December 2019
41 Kahn Instruments