Sample Pipe; Gasses To Avoid; Sample Conditioning; Pressure And Flow Control - Alpha Moisture Systems SADPmini Instruction Manual

7.1 Sample Pipe

The SADPmini is supplied with 2 connections: a "fir tree" on one side and a Swagelok
compression fitting for
other. Either can be used as the inlet connection (6).
PTFE and stainless steel are recommended materials for sample pipes. Some specialist
flexible tubing may be suitable as sample pipe, but common flexible tubing, such as
pvc, nylon, polythene or rubber, should not be used, as they are permeable, and water
vapour from the atmosphere will diffuse through them into the sample gas.
A 2m PTFE sample pipe is supplied for use with the "fir tree" connection. The first
time this is used it is advisable to warm the end that will go over the "fir tree" for a few
seconds with a heat source to soften it slightly, which helps to get a gas tight seal.

7.2 Gasses to avoid

Corrosive Gases: The Sensor should not be exposed to corrosive gases (or corrosive
contaminants in the gas sample) as these can chemically attack the sensor, impairing
calibration accuracy and/or damaging it beyond economic repair. Examples of such
gases are mercury (Hg), ammonia (NH
such as ozone (O
Sulphur hexaflouride (SF
arcing, however, it is possible that various acidic species will have been formed that
will corrode the sensor. When testing SF
acidity test should be carried out first; if the gas proves to be acidic then the moisture
test should not be carried out.

7.3 Sample conditioning

The main principle when considering the presentation of the gas sample to a portable
dewpoint meter is to keep the sample system as simple as possible and of minimum
swept volume, so that it has the least possible influence on the gas sample.

7.4 Pressure and flow control

In most cases the gas to be sampled will be at a positive pressure, which will need to be
reduced to atmospheric pressure. At low pressures, up to around 10 barg, this can be
done by including a simple needle valve (5) to control the flow and thereby, the
pressure dropping across it. Ideally this would be the isolation valve (1) on the sample
1 1
/ in, / in, or 6mm OD pipe (as specified on your order) on the
4 8
) should also be prevented from coming into contact with the sensor.
3
) has no effect on the sensor. If the gas has been exposed to
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), chlorine (Cl ) etc. Strong oxidising agents
3 2
that may have been arced, therefore, an
6
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