Michell Instruments SF82 Series, User Manual

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SF82 Transmitter User’s Manual
97576 Issue 1, June 2019 12
Dead volumes (areas which are not in a direct flow path) in sample lines, hold onto water
molecules which are slowly released into the passing gas. This results in increased purge and
response times, and wetter than expected readings. Hygroscopic materials in filters, valves (e.g.
rubber from pressure regulators) or any other parts of the system can also trap moisture.
Plan your sampling system to ensure that the sample tap point and the measurement point are
as close as possible to avoid long runs of tubing and dead volumes.
Filtration
All trace moisture measurement instruments and sensors are by their nature sensitive devices.
Many processes contain dust, dirt or liquid droplets. Particulate filters are used for removing dirt,
rust, scale and any other solids that may be in a sample stream. For protection against liquids, a
coalescing or membrane filter should be used. The membrane provides protection from liquid
droplets and can even stop flow to the analyser completely when a large slug of liquid is
encountered, saving the sensor from potentially irreparable damage.
2.5.3. Transmitter Mounting
Once an installation location has been chosen, this point will require a thread to match the
transmitter thread. Fixing dimensions are shown in Figure 6. For circular pipework, to ensure the
integrity of a gas tight seal, a mounting flange will be required on the pipework in order to provide
a flat surface to seal against.
Figure 12 Transmitter Mounting - Pipe or Duct