Vaisala HMP240 - Manual (Page 45)

HMP240 series
M210300en User's Guide
43
A
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13.5 mm adapter must be used when calibrating with the HMK13B
calibrator. The adapter (part no. 16611) can be ordered from Vaisala or
Vaisala representatives.
Calibration can be performed by giving the commands with the press switches
inside the housing (see Chapter 5.2), through the serial bus (see Chapter 5.4)
or through the menus on the local display (see Chapter 5.3).
When LED commands are used and when the two analogue channels do not
output either relative humidity and/or temperature, relative humidity is cali-
brated on channel 1 and temperature is calibrated on channel 2. The calibra-
tion ranges are 0...100 %RH and -20...+80 °C. When the transmitters are cali-
brated at two points, the points must be either 50 %RH or 50 °C apart from
each other.
NOTE
If the transmitter includes the re-gaining option, the
sensor re-gaining must always be done before humidity
calibration. Before starting the calibration make sure
that the temperature of the composite sensor has come
down to ambient temperature (see Appendix 7).
6.1.1 One point humidity calibration
The HMI38 humidity data processor can be used as a one-point field calibra-
tor. A two-point calibration with the HMI38 can also be done, provided that
two separate humidity points with a difference of more than 50%RH between
them are available. The HMI38 is connected to an HMP240 transmitter using
an appropriate reference connection cable. The necessary correction factors
are automatically stored in the HMP240 memory. Detailed calibration
instructions are given in the HMI38 operating manual.
A manual one-point correction can also be done in the field against an accu-
rate reference.
NOTE
If the sensor has been changed, the calibration has to be
done according to the instructions in Chapter 6.1.3.