Michell Instruments QMA401, Руководство пользователя

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QMA401 User’s Manual
Michell Instruments 41
OPERATION
• Pipe material surface finish
Components with a smooth mechanical finish are always preferred. Do not confuse the
term electro-polished with a mechanical polishing procedure. Electro-polishing normally
is preceded by mechanical polishing to achieve the best results. If a choice of finish
is available for the materials dictated by the process or sample system, select the
smoothest for faster response.
• Pipe diameter
The larger the sampling pipe diameter, the more exposed the gas will be to the pipe wall.
Therefore it is recommended to use the smallest possible pipe diameter to minimize the
previously mentioned effects. This must be balance with the desired response speed.
Depending on the configuration 1/8” pipe diameter is recommended. Please contact
Michell Instruments if further recommendations are needed.
• Ambient temperature variation
The QMA401 is extremely sensitive to moisture fluctuations and ambient temperature
variations will affect the equilibrium conditions. In a stable environment, the water
vapor pressure within a closed system is in equilibrium with the outside ambient. If the
ambient temperature increases, the energy is imparted to the gas pipes and the water
molecules within the wall. This additional energy will upset the original equilibrium and
the increased pressure water in the walls migrates in towards the drier gas stream.
Small molecules such as water will migrate through the pipe wall until the entire system
reaches a new equilibrium. It is possible to minimize this effect on a sampling system
by heat tracing sample lines and insulating/heating the sampling system enclosure to a
stable temperature above the maximal ambient temperature.
It is important to control the temperature of all components of the sampling system,
including regulators and lines. For this reason it is strongly advised to use heat traced
line to eliminate this temperature change effect and measure moisture content solely
related to the gas under test.