Vaisala HMT120 - Manual (Page 61)

Chapter 5 _______________________________________________________________ Maintenance
VAISALA ________________________________________________________________________ 59
Adjustment with HMI41
You can check and adjust the HMT120 relative humidity measurement
with the HMI41 indicator and HMP41/45/46 probes. A HMI41-
connection cable is needed. Vaisala order code: 25917ZZ.
There are three adjustment modes available: offset (dry point), gain (wet
point), and two-point adjustment. All of these can be performed using the
HMI41 either as a reference meter (for example when the transmitter is
mounted in an air-conditioning channel) or only as a terminal for
visualizing and setting the transmitter's RH reading.
Offset and gain adjustments are performed the same way and differ only
in internal calculations. Select offset adjustment when the reference
humidity is < 65 %RH and gain adjustment when the reference humidity
is ≥ 65 %RH. Two-point adjustment is more accurate, and includes both
offset and gain corrections. For performing two-point adjustment, you
need two separate measurement points with a difference of at least 50
%RH between them.
Follow the general directions of connecting the HMI41 to the HMT120
and selecting the HMI41 calibrator function and then continue according
to the chosen adjustment method.
0505-187
Figure 20 Location of the HMI41 Calibration Connector
The following numbers refer to Figure 20 above:
1 = HMI41 indicator
2 = EXT connector
3 = 25917ZZ connection cable
1
2
3