Vaisala HMT120 - Manual (Page 53)

Chapter 5 _______________________________________________________________ Maintenance
VAISALA ________________________________________________________________________ 51
30 %RH. The difference between the two temperature reference points
must be at least 30 °C.
NOTE In push-button calibration, the transmitter outputs are by default relative
humidity in the range 0…100% RH in CH1 and temperature in the range
-40 … +80 °C in CH2 regardless what the actual transmitter settings are.
Outputs mean in this case both the display and analog current outputs.
Humidity and Temperature Adjustment
To make a humidity or temperature adjustment (the same instructions
apply to both one-point and two-point calibration):
1. Open the transmitter cover and you can see three buttons
marked ADJ, + and -. There are also two indicator LEDs, one
green and one red on the HMT120 motherboard.
2. Press the ADJ button and hold it down until the green indicator
LED begins to blink slowly (800ms cycle time).
3. HMT120 transmitter is now in RH calibration state. Analog output
and optional display will still follow the actual measured RH value.
NOTE If you do not wish to perform the RH adjustment at this time, press ADJ
button one more time. The green indicator LED turns off and the red
indicator LED begins to blink slowly (800ms cycle time) to indicate T
calibration state. Now you can continue following the instructions from
step 7 onward.
4. Remove the filter and insert the probe into a measurement hole of
the dry end reference chamber (for example, LiCl: 11 %RH) to do
the low humidity offset adjustment.
NOTE Do not touch the adjustment buttons before the conditions have
stabilized. This takes approximately 30 minutes.
5. Press either the - or + button at least once, make sure that the I
out
current is correct, adjust using the - and + buttons if needed, and
press the ADJ button again. The green indicator LED begins to
blink faster (400ms cycle time).