User`s guide

Chapter 9 _______________________________________ Calibration, Adjustment, and Maintenance
Adjusting Dewpoint
Before adjusting dewpoint, first carry out the two-point, relative
humidity calibration, which will ensure the basic adjustment level.
When adjusting the DMP74B or DMP74C probe or DMT340 series
transmitters with the M-sensor, do the sensor purge before calibration
and adjustment. For details, see section Sensor Purge on page 29.
Two-Point Relative Humidity
Adjustment
NOTE
For probes DMP74A, the wet point humidity reference must be >20
%RH.
For probes DMP74B and DMP74C, the wet point humidity reference
must be <20 %RH.
For DMP74A, the humidity references of 0 % (for example Nitrogen)
and 30 ... 75 % are recommended. Make sure that the difference
between the humidity references is more than 30 %.
For DMP74B and DMP74C, the humidity references of 0 % (for
example Nitrogen) and 11 % are recommended.
To make the adjustment, follow the instructions below:
1. Check that DM70 is turned on.
2. When using the DMP74B probe, do the manual sensor purge.
For details, see section Manual Sensor Purge on page 31.
3. Unscrew the screw from the probe handle to expose the
calibration button (see num
ber 4 in Figure 1 on page 11). Then
press the button with a sm
all screwdriver. When pressing the
button, the indicator switches into the adjustment mode.
4. To start adjusting, press OK.
5. Then select RH and press Select.
6. To check the environmental settings, press Yes. To continue
without checking the settings, press No.
VAISALA _______________________________________________________________________ 67