The following steps describe the process of setting the auto cal, describing the two different
methods where different.
Note:- The SDT must be connected to its normal indicator so that readings can be
taken or, where no indicator is employed, an accurate measurement of the mA
output must be taken.
9.1.4 Pre-conditioning the transmitter
To perform the auto cal, the transmitter needs to be removed from the process gas ready to
be saturated in the hand, or inserted into a known gas flow. At this stage, the
display/indicator will read the ambient dewpoint as measured by the SDT.
Saturating the Transmitter method (Only applicable to C and F SDT transmitters)
Saturate the transmitter by lightly covering the sintered aluminium area with a hand for
approximately 1 minute.
Expose to a known moisture level. (Applicable to C and F SDT transmitters)
Expose the transmitter to the known auto cal moisture level and allow the transmitter to
attain equilibrium. (For technical questions and advice on the time taken to attain
equilibrium, contact your SDT supplier)
9.1.5 Adjust the Auto Cal
Once the transmitter has been pre-conditioned the potentiometer can be adjusted. ONLY
ADJUST THE POTENTIOMETER IF THE SENSOR IS PROPERLY PRE-CONDITIONED.
FAILURE TO COMPLY WILL CORRUPT THE TRANSMITTERS CALIBRATION.
In case of a transmitter saturated in the hand, the display should read +20C (or 20mA if
reading current).
Note:- Always dry the output level down below 20C before wetting back up to
exactly 20C.
If a known dewpoint is applied, then this value should be displayed.
9.1.6 Completing the Auto Cal
Once the desired value is reached, the auto cal process is completed and the screw driver
should be removed from the potentiometer and the weatherproof guard should be replaced
and fastened using the large silver coloured screw. If using the saturated transmitter
method, the transmitter can be put down on a work bench.
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