Vaisala HMT120 User Manual download pdf (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 c

an 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

o 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).

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Vaisala HMT120 User Manual Page 53