Chapter 5 _______________________________________________________________ Calibration
NOTE
During the calibration with HMI41, please note that temperature loop
current is not within the scaling.
With Pushbuttons and a Jumper
You can also perform the calibration with pushbuttons and a jumper on
the component board (see Figure 5 on page 24). In addition, you need a
digital multimeter (DMM). There are two push buttons (UP and DOWN)
and four pairs of pins (RH offset, RH gain, T offset, and T gain), which
are connected with the calibration jumper. Vaisala recommends using the
RH offset pins if the RH is less than 65 %RH and the gain pins if the RH
is greater than 65 %RH.
For example, to perform a one-point humidity calibration using saturated
NaCl salt solution at 75.5 %RH as a reference, do as follows:
1.
Insert the probe into a NaCl salt chamber and let stabilize.
2.
Connect a DMM to the RH current loop and wait until the reading
stabilizes.
3.
Connect a jumper to the RH gain pins and adjust the DMM reading
with buttons UP and DOWN until the loop current corresponds to
75.5 %RH.
4. Disconnect
the
jumper.
Two-Point Humidity Calibration
You can also perform a two-point calibration with saturated salt
calibrators (for example HMK15), or you can send the instrument to
Vaisala or a Vaisala representative for recalibration. Figure 6 on page 26
illustrates the difference between offset and gain calibrations.
Two-Point Humidity Calibration Procedure
1.
Leave the calibrator and the probe for at least 1 hour in the same
environment so that their temperatures have time to equalize. For
information on more accurate stabilization times, see Chapter 4,
Installation, on page 17.
2.
Insert the probe into the measurement hole of the LiCl salt chamber
in the humidity calibrator.
3.
Wait for 20 to 40 minutes.
4.
Check the temperature and read the closest corresponding RH
value in the calibration table (Table 5 on page 25)
VAISALA _______________________________________________________________________ 23
