Michell Instruments Easidew Online, Руководство пользователя

Страница: 49 / 68

Easidew Online User’s Manual
Michell Instruments 41
MAINTENANCE
4.1 General Operational Guidelines
General guidelines to be followed when setting-up a sampling system are as follows:
• Transmitter Positioning
The sample point should be as close to the critical measurement point as possible. Also,
never sample from the bottom of a pipe as entrained liquids may be drawn into the
sensing element.


Figure 31
Installation Location
• Avoidance of Dead Spaces
Dead space causes moisture entrapment points, increased system response times and
measurement errors, as a result of the trapped moisture being released into the passing
sample gas and causing an increase in partial vapor pressure.
Deadspace

Figure 32
Indication of Dead Space
• Particulate and Oil Removal
Particulate matter at high velocity can damage the sensing element and similarly, at
low velocity, they may ‘blind’ the sensing element and reduce its response speed. If
particulate, such as degraded desiccant, pipe scale or rust is present in the sample gas,
use an in-line fi lter.
• High Quality Tube and Fittings
Michell Instruments recommends that, wherever possible, stainless steel tubing and
fi ttings should be used. This is particularly important at low dew points since other
materials have hygroscopic characteristics and adsorb moisture on the tube walls,
slowing down response and, in extreme circumstances, giving false readings. For
temporary applications, or where stainless steel tubing is not practical, use high quality
thick walled PTFE tubing.