Michell Instruments Easidew DryCheck, Руководство пользователя

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Easidew DryCheck User’s Manual
22 97108 Issue 13, July 2017
OPERATION
4 GOOD MEASUREMENT PRACTICE
The Easidew DryCheck 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 ceramics or base metals then
it will be suitable for measurement by the Easidew DryCheck.
The system is designed for operation with sample gas flow rates of 1 to 5 Nl/min (2.1 to
10.6 scfh) (sample block). Ideally, the flow rate should be set-up between 4 and 6 Nl/
min. Flow regulation is provided within the Easidew DryCheck system. Always use high
quality valve gear, coupling connections and pipework.
The system will operate successfully at flow rates within its operational range and it is
important to ensure that the flow rate through the sample block is high enough to avoid
long time lags in response to humidity changes at the sample source.
Avoid pressure gradients in the system by placing excessive flow restriction on the
output side of the sample block. In applications where the test gas has a very high
flow rate, an instrument by-pass arrangement is preferable to flow restriction after the
transmitter.
Flow Rates
Theoretically flow rate has no direct effect on the measured moisture content, but in
practice it can have unanticipated effects on response speed and accuracy.
An inadequate flow rate can:
• Accentuate adsorption and desorption effects on the gas passing
through the sampling system.
• Allow pockets of wet gas to remain undisturbed in a complex sampling
system, which will then gradually be released into the sample flow.
• Increase the chance of contamination from back diffusion: ambient air
that is wetter than the sample can flow from the exhaust back into the
system. A longer exhaust (sometimes called a pigtail) can also help
alleviate this problem.
• Slow the response of the sensor to changes in moisture content.
An excessively high flow rate can:
• Introduce back pressure, causing slower response times and
unpredictable effects on equipment such as humidity generators.
Factory Flow Rate Setting
Internally the gas enters a sample block at which point an adjustable flow valve is
located. This valve is factory set to output 2.5 l/min flow at 7 barg.