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.|
The procedure below provides an example adjustment of offset and gain using the Vaisala Humidity Calibrator HMK15, which is a saturated salt calibrator. It is assumed that the module is powered and you can measure the analog output reading.
|For best results, use the ACAL command to calibrate the currently active analog output mode before using the trimmers. For instructions on how to do this, see Calibrate Analog Output.|
- 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
- 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 steps 2 – 4 to check the adjustment result. If you want to undo the adjustment, return the trimmers to their original position.