HMP45A and HMP45D
Operating Manual U274en-1.2
2
3. CALIBRATION AND MAINTENANCE
Calibration and maintenance of the probes should be performed at regular
intervals, depending on the conditions of use and desired accuracy. The
recommended calibration interval is one year.
The HMP45A/D probes are easy to maintain and calibrate. The probe consists
of a probe head and a handle with cable. All calibration electronics are in the
probe head which can be disconnected from the handle without disconnecting
the wires (see Figure 2). The handles of all HMP45A and HMP45 probes are
fully interchangeable. If you wish to continue the measurement immediately,
you can insert a calibrated probe head in place of the disconnected one; this
way, the measurement is interrupted for less than a minute.
3.1 Reading the outputs during calibration
ENTERMODE HO LD ON/OFF
HMI41HMH45
D
W
T
NOTE:
remove the O-ring if you
connect the probe directly
to the HMI41 indicator
pull the probe head
off the handle
adjustment trimmers:
W = wet D = dry
(T = temperature; for
factory use only!)
Figure 2 Adjustment trimmers and probe head connection/disconnection
In calibration, the HMP45A/D output is normally read from the output cables.
The HMP45A probe head can also be checked with Vaisala’s HMI41 indicator
(see Figure 2); the probe head can be connected either to the HMH45 handle,
or directly to the HMI41 indicator. However, note that if you connect the
probe head directly to the HMI41, you must first remove the O-ring. Measured
humidity and temperature appear on the HMI41 display.
A simple field check can also be performed when there seems to be something
wrong with the measurement system. It is sufficient to compare the HMP45A
reading with the reading measured by a calibrated reference probe head. Check
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