SADP_Operating_ Instructions_0114
6.0 Normal Operation
Brief operating instructions will be found on the label fastened to the top of the instrument cabinet. The
standard test procedure is as follows:
1. Switch the instrument on, and check the battery condition.
2. At the sample point to be tested open the sample valve or regulator slightly and check that no dirt or
condensate is expelled. [If any dirt or condensate is present, wait until it is cleared, or abandon the
test].
The pressure of the sample source is not important: however the instrument needs a small sample
of the air or gas which has been reduced to atmospheric pressure at the sample point (It must
not exceed 5 PSI for safe operation) - easily achieved by opening the valve just enough to allow a
small flow to escape through the dewpoint meter.
3. Connect the PTFE sample pipe supplied with the instrument between the sample tapping point and
the instrument, using either of the connections of the head/sensor assembly.
4. Adjust the sample valve or regulator to give a gentle flow through the instrument, [5/10 L/min. is
ideal — but the flow rate is not particularly critical. Do not exceed a flow of about 20 L/min].
5. Allow the sample to flow for 2 or 3 minutes in order to purge the sample pipe (a longer time might be
needed if testing very dry gas - drier than about -65 c. dewpoint). Then place a finger over the outlet
connection of the instrument head, and the sample pressure will cause the head to open. Remove
finger from the instrument when the head is fully open. [If there is insufficient sample pressure, fit a
length of 1 or 2 metres of flexible pipe to the outlet connection of the instrument head, and slowly
raise the head by hand].
6. The instrument reading will move up the scale (wetter), and stabilise. When there is no further
change in reading, note the result. If the reading moves up the scale (wetter) and then moves down
the scale (drier) then either the sample pipe was not purged enough before the head was raised, or
the sample is becoming drier during the test. (Perhaps by taking the sample from a pipe in which the
gas has been stagnant for some time).
If in doubt about the suitability of the sample flow rate, or the materials of the sample pipe being used,
increase the sample flow rate after the final reading has been obtained. If the instrument moves to a
drier reading this indicates that the original flow rate was too low, or that there is a leak in the system
allowing ambient moisture into the sample, or that the sample pipe is still wet.
7. After the test is complete, and if continuous reading is not needed, close the instrument head ready
for the next test.
8. Note these instruments are designed for rapid moisture determination when operated from Dry to
Wet, in this case they should give a 95% step change within 30 seconds. When operated Wet to Dry
we cannot quote any response time as this is dependant upon many variables but will be
considerably longer than the Dry to Wet response time.
Dual Range Model TR
This model should be operated in the same way as the standard range model except that when the
reading has stabilized you can move the switch from STD RANGE to LOW RANGE. This will activate
the lower red scale marked WATER VAPOUR. This is simply an amplification of the middle green
scale marked PPM (V) and will display a more accurate reading between the range of 0-10ppm.
PLEASE NOTE: When performing the Automatic Calibration procedure the switch must be returned to
the STD RANGE position.