HMM100 series modules have two trimmers mounted on the component board. These trimmers
allow for easy adjustment of the offset and gain of the humidity measurement.
The modules are shipped with the trimmers centered.
Turning the trimmer counter-clockwise will
decrease the offset or gain, and turning clockwise will increase it. The adjustment range is
±5 % for both offset and gain.
Offset correction requires a < 50 %RH
reference. Offset and gain correction requires additionally a > 50 %RH reference, with
over 30 %RH difference between the two points.
The trimmers will only turn 135 degrees each way, less than half a rotation.
Do not force the trimmer past the stopping point.
Figure 1. Trimmers for Offset and Gain
The procedure below provides an example
adjustment of offset and gain using the saturated salt calibrator HMK15. It is assumed that
the module is powered and you can measure the output reading.
Note the current position of the trimmers.
Insert the probe in the LiCl salt chamber of the humidity calibrator (11 %RH), and wait
for 20 – 40 minutes for the reading to stabilize.
If necessary, adjust the offset trimmer using a small Phillips-head screwdriver
to achieve the output reading that corresponds to 11 %RH.
For 4 ... 20 mA output, the reading should be 5.76 mA
For 0 ... 5 V output, the reading should be 0.55 V
Insert the probe in the NaCl salt chamber (75 %RH) and wait for the reading to
stabilize.
If necessary, adjust the gain trimmer to achieve the output reading that
corresponds to 75 %RH.
For 4 ... 20 mA output, the reading should be 16 mA
For 0 ... 5 V output, the reading should be 3.75 V
Optional: repeat step 2 - step 4 to check the adjustment result. If you want to undo
the adjustment, return the trimmers to their original position.
