Connect the SDHmini. The SDHmini is not flow sensitive, however, the sample
flow needs to be enough to fill the sensor head with gas effectively, so anything
less than 1 litre/min would mean that the instrument would take too long to settle
to a stable reading. The flow should not be so high that the gas velocity could
physically damage the sensor or cause back-pressure in the sensor head, so should
not exceed approximately 10 litres/min.
3.6 Using the SDHmini to Take a Moisture Reading
The first purpose of the SDHmini is to provide a rapid, easy and reliable means of
carrying out moisture content measurement of gases. To ensure rapid response
the sensor is kept dry by surrounding the sensor with desiccant in the head
assembly when it is not in use.
After purging the system to be monitored fit the SDHmini sample pipe to the
sample connection (6). Allow the gas to purge for a further two minutes with the
head down. Restrict the outlet of the SDHmini (7) by placing a finger over the
sample exhaust (9), so that the pressure of the sample lifts the telescopic head.
As soon as the head is fully extended remove the finger, to prevent pressure build
up. Pull gently on the head to make sure it is fully extended. If there is not enough
pressure to lift the head assembly, assist it by pulling it up, do this very slowly so
that ambient air is not drawn in through the outlet.
The sensor will respond to the moisture level present in the sampled gas. The
displayed moisture value will continue to change until the sensor reaches
equilibrium at which point the displayed value is representative of the moisture
level in the sampled gas. When a reading has been taken and the test is finished,
push down the telescopic head fully, carefully turn off the sample flow and
disconnect the sample pipe. With the head in the down position the desiccant will
dry the sensor, ready for the next test.
Note
: It is important that the head assembly is either fully up or fully down to
keep the desiccant isolated from the ambient air so avoiding wetting it. When the
instrument is not in use it should be stored with the head in the down position.
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