Michell Instruments QMA601, User Manual

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QMA601 User’s Manual
46 97449 Issue 3, June 2018
OPERATION
Figure 40
About Screen
The service pages are intended for Michell Instruments approved personnel only. They
do not contain any user accessible functions.
3.8 Sampling Guidelines
The QMA601 is designed to operate in a flowing gas stream and is suitable for the
measurement of the moisture content of a wide variety of gases. In general, if the
gas (in conjunction with water vapor) is not corrosive to the sampling system and the
sensor base metals then it will be suitable for measurement by the QMA601.
The analyzer is designed to automatically regulate the sample flow rate. However,
the sample pressure and back pressure must match what is shown on the calibration
certificate (typically 3 barg (43.5 psig) sample pressure, 2 barg (29 psig) back pressure),
and should be controlled using a high-quality pressure regulator on the gas inlet and a
back pressure regulator on the outlet.
Dried samples and wet samples are alternately passed through the sensor cell. The
difference in the measured beat frequency produced by the wet and dry samples is
proportional to the moisture content in ppm
V
of the gas being analyzed.
General guidelines to be followed when setting-up a sampling system are as follows:
• Ensure that the sample is representative of the gas under test
To ensure 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
analyzer’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 passing
sample gas, producing an increase in partial vapor pressure.