Vaisala DM500 - Manual (Page 62)

User's Guide ______________________________________________________________________
60 __________________________________________________________________ M210205EN-D
Forced Freezing
In some measurement conditions there may be formation of a two
phase system, ice-dew, on the sensor. This situation is dynamic and
the time needed to reach an equilibrium may be rather long. To avoid
an unstable phase transition, the DM500 has a function for generating
a stable layer of frost on the sensor right from the beginning of the
measurement.
When turned on, the forced freezing procedure is automatically
enabled when measurement is started. However, the forced freezing
procedure may also be turned off by the user, if so desired.
The automatic forced freezing procedure recognizes the temperature at
which condensation begins to form on the sensor surface. The control
of the forced freezing procedure is based on this temperature, and
therefore the dewpoint of the measured gas should be stable during the
freezing procedure. If forced freezing is enabled and the frostpoint is
ca. -6...-30 ºC, the procedure will freeze the sensor cold enough for the
condensation to form a stable layer of frost. Use of forced freezing
may lengthen the measurement start-up time.
If forced freezing is disabled by the user, in certain conditions
formation of an unstable phase system on the sensor is possible.
1. Open MENU : press .
2. Select ► Measuring , press
3. Select ► Measurement settings , press .
4. Select Forced freezing .
5. To enable the function, press ON .
6. To disable the function, press OFF .
7. Press EXIT to return to the main view.
Cooling Method Air/Water
Select the cooling method air ( ) or water ( ) by using this function.
Water cooling is recommended when measuring dewpoints below
-50 ºC (-58 ºF) or above +40 ºC (104 ºF).
This selection optimizes the operation of thermoelectric coolers.