Kahn Easidew Plus User Manual page 16

Easidew Plus Portable Hygrometer User's Manual
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. The optimal
flow rate varies depending on the measurement technology, and can always be found
in the instrument or sensor manual.
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.
• Result in a reduction in heating capabilities of the sensor tile during the
initialization period. This is most apparent with gases that have a high
thermal conductivity such as hydrogen and helium.
Which Gases to Measure?
The Easidew Plus Portable Hygrometer is suitable for 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.
!
!
Kahn Instruments
POSSIBLE INJURY! The tubing, valves and other apparatus
attached to this instrument must be adequate for the
maximum pressure which will be applied, otherwise physical
injury to the operator or bystander is possible.
Before disconnecting the Easidew Plus Portable Hygrometer
from the gas line it is essential to vent the system to
atmospheric pressure, otherwise severe injury could result.
GOOD MEASUREMENT PRACTICE
11