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June 2003
A-4
Application of the Hygrometer (900-901D1)
Response Time (cont.)
To minimize any adverse affects on response time, the preferred
materials of construction for moisture monitoring sample systems are
stainless steel, Teflon
®
and glass. Materials to be avoided include
rubber elastomers and related compounds.
Temperature
The GE Panametrics hygrometer is largely unaffected by ambient
temperature. However, for best results, it is recommended that the
ambient temperature be at least 10°C higher than the measured dew
point, up to a maximum of 70°C. Because an ambient temperature
increase may cause water vapor to be desorbed from the walls of the
sample system, it is possible to observe a diurnal change in moisture
concentration for a system exposed to varying ambient conditions. In
the heat of the day, the sample system walls will be warmed by the
ambient air and an off-gassing of moisture into the process fluid, with
a corresponding increase in measured moisture content, will occur.
The converse will happen during the cooler evening hours.
Flow Rate
GE Panametrics hygrometers are unaffected by the fluid flow rate.
The moisture probe is not a mass sensor but responds only to water
vapor pressure. The moisture probe will operate accurately under
both static and dynamic fluid flow conditions. In fact, the specified
maximum fluid linear velocity of 10,000 cm/sec for The M Series
Aluminum Oxide Moisture Sensor indicates a mechanical stability
limitation rather than a sensitivity to the fluid flow rate.
If the measured dew point of a system changes with the fluid flow
rate, then it can be assumed that off-gassing or a leak in the sample
system is causing the variation. If secondary moisture is entering the
process fluid (either from an ambient air leak or the release of
previously absorbed moisture from the sample system walls), an
increase in the flow rate of the process fluid will dilute the secondary
moisture source. As a result, the vapor pressure will be lowered and a
lower dew point will be measured.
Note:
Refer to the
Specifications
chapter in this manual for the
maximum allowable flow rate for the instrument.
Содержание Moisture Image 1 Series
Страница 2: ...Moisture Image Series 1 Service Manual ...
Страница 8: ...Chapter 1 ...
Страница 31: ...Chapter 2 ...
Страница 61: ...Appendix A ...
Страница 94: ...June 2003 A 32 Application of the Hygrometer 900 901D1 Figure A 2 Moisture Content Nomograph for Liquids ...