Vaisala HMP155 - Manual (Page 61)

Chapter 6 ___________________________________________________Calibration and Adjustment
VAISALA _______________________________________________________________________ 59
Push-Button Calibration
Calibration and adjustment of the HMP155 can be done by using the
adjustment buttons found on the probe. The two-point humidity
adjustment is carried out by using two relative humidity references: for
example saturated salt points 11 % RH (LiCl) and 75 % RH (NaCl). The
difference between the two humidity reference points must be at least 30
%RH. The difference between the two temperature reference points must
be at least 30 °C.
NOTE In push-button calibration, the probe outputs are by default relative
humidity in the range 0…100 %RH in CH1 and temperature in the range
-40…+60°C in CH2.
Two-Point Humidity and Temperature
Adjustment
To make a humidity or temperature adjustment:
1. Carry out the chemical purge (if available). See section Chemical
Purge (Optional) on page 45.
2. Uncover the adjustment buttons on the probe by removing the
protective cover and removing the calibration seal.
3. Open the protective plug and you can see three buttons marked -, □
and +. There is also a two-colored indicator LED. See Figure 13 on
page 58.
4. Press the ADJ button and hold it down until the green indicator
LED lights up. This puts HMP155 in RH calibration mode.
5. 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.
6. Using the - and + buttons, make sure the A
out
voltage is correct and
press the ADJ button. Green indicator LED turns off and back on.
NOTE Do not touch the adjustment buttons before the conditions have
stabilized.