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HygroPort I.S. User’s Manual
6 GOOD MEASUREMENT PRACTICE
The HygroPort I.S. is designed to operate in a flowing gas stream with flow rates
between 0.4 and 1.0 scfh (0.2 and 0.5 Nl/min). Flow regulation is provided with the
HygroPort I.S. instrument up to a 10 barg limit. Beyond this the sample flow must
be regulated outside the unit.
There are a number of options for sample conditioning including a specifically designed
sampling system and a variety of application kits. The fl low rate can be regulated on
the inlet or outlet depending on whether the intention is to measure at atmospheric
or sample pressure. Up to 150 psig (10 barg), this can be achieved by use of the orifice
fittings supplied with the instrument. Section 3.5.1 and Figure 3.4
show a typical
arrangement for measuring non-hazardous gas at atmospheric or elevated pressure.
In applications where the sample gas has a very high fl low rate it is advisable to use
an instrument by-pass arrangement to provide the minimal fll low rates which the sensor
requires. Excessive fl low restriction can cause back-pressure across the sensor leading
to a discrepancy between the readings recorded and those expected.
Measurement of Dewpoints Drier than -70°Cdp
The HygroPort I.S. Sampling System is optimized for fast response. Therefore,
when measuring very dry dewpoints, certain steps need to be taken to insure that the
best accuracy is achieved:
1. Remove the sintered filter from the inlet port.
2. Make sure that all tubing and fittings used are made from stainless steel.
The purpose of this is to reduce the possibility of any moisture being trapped upstream
of the sensor; prolonging the dry-down process; or permeating into the sample line
through unsuitable tubing - such as PTFE.
Due to the significantly lower levels of moisture present at dewpoints of this level, the
response times of the sensor will be significantly increased. The table below offers an
approximate guide to the times taken for the instrument to stabilize at a given dew
point (from a starting point of 10°Cdp ambient):
Target Dewpoint T100 response time from ambient (hours)
-112°F (-80°C) 12
-130°F (-90°C) 48
-148°F (-100°C) 96
Issue 6, December 2019 40 Kahn Instruments