Vaisala DMT340 - Manual (Page 138)

User's Guide _______________________________________________________________________
136 __________________________________________________________________ M210704EN-G
Sensor Functions
AutoCal
To obtain the best possible accuracy in measurements taken in dry
environments, DMT340 has a built-in AutoCal. During the AutoCal,
DMT340 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 <2 % (DMT340 DRYCAP® M-sensor).
- Temperature must be 0<T<80 ºC (or sensor warming activated for -
40<T<80 ºC).
- 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 DMT340 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.