Vaisala HMM100 - Manual (Page 55)

Chapter 5 _______________________________________________________________ Maintenance
VAISALA ________________________________________________________________________ 53
Calibration
The recommended calibration interval is one year. You should also
perform a calibration if the HMM100 does not appear to be within the
specified accuracy.
The HMM100 can be adjusted in two ways:
- Using the onboard trimmers. This method requires no serial
connection, only a small Phillips head screwdriver and a suitable
humidity reference. The trimmers can adjust up to ± 5% of reading.
- Using serial commands. This method requires a connection to the
service port of the HMM100 module. For this, you need the USB
cable (Vaisala order code: 226068) and a PC with a terminal
application. You also need a humidity reference and a Phillips head
screwdriver for zeroing the trimmers.
As a humidity reference, you can use, for example, the Vaisala Humidity
Calibrator HMK15.
Installing the probe properly will also help with the calibration. Ideally
the probe should be placed completely in the environment, with enough
cable to prevent heat conduction, and to allow the probe to be moved
during calibration (placed in the HMK15 calibrator, for example).
NOTE If you have changed the HUMICAP® sensor, center the trimmers, and
perform a calibration and adjustment using the serial command CRH.
NOTE You can only calibrate the humidity measurement (RH) and temperature
measurement (T). The module calculates the dewpoint using RH and T
values.