Vaisala DMT346 - Manual (Page 131)

Chapter 4 _________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 131
Sensor Functions
AutoCal
To obtain the best possible accuracy in measurements taken in dry
environments, DMT345 and DMT346 have a built-in AutoCal feature.
During the AutoCal, the transmitter adjusts the dry-end reading to
correspond to the calibrated values. This is a unique and patented method
to avoid errors in accuracy when monitoring low dewpoints.
The AutoCal is carried out if the following criteria for the measurement
environment are fulfilled:
- Relative humidity must be <10 %.
- Temperature must be 0
- Humidity environment must be stable. The maximum change in the
dewpoint can be 2 ºC in 15 seconds.
NOTE AutoCal cannot operate if the above conditions are not fulfilled.
If the adjustment in the AutoCal reaches a preset maximum value or if
the AutoCal correction fails, for example, because of unstable conditions,
a new AutoCal will take place later (if the automatic AutoCal is turned
on).
Automatic AutoCal
As a default, the automatic AutoCal in DMT345 and DMT346 is turned
on. In this mode, the calibration takes place automatically if the dewpoint
or temperature changes significantly, typically more than 10 ºC.
However, if there are no changes in the conditions, the AutoCal will take
place repeatedly after one hour from the last AutoCal.
Manual AutoCal
To ensure that AutoCal has taken place for obtaining the most accurate
measurement in a very dry environment, you can perform Autocal
manually before measuring as follows:
1. Open the Main Menu
by pressing any of the ▲▼◄► arrow
buttons.
2. Select Measuring
, press the ► arrow button.
3. Select Manual AutoCal
, press the ► arrow button.