Chapter 2 ___________________________________________________________ Product Overview
VAISALA________________________________________________________________________ 17
Basic Features and Options
DMT345/346 has the following basic features and options:
- Dewpoint measurement with AutoCal and sensor purge features.
- Sensor warming in high humidities.
- Two analog outputs and a serial interface, optional third analog
output.
- Installation accessories
- DMT345: mounting flange,
- DMT346: cooling set for high temperature applications.
- User friendly multilingual display option.
- Different sensor protection options and probe cable lengths 2 m,
5 m or 10 m.
- Optional modules: galvanic isolation for outputs, AC mains power
supply, RS-485 serial line, relay module.
Operating Principle
The DMT345/346 transmitter incorporates the Vaisala DRYCAP
®
sensor, which uses an operating principle based on changes in
capacitance as its thin polymer film absorbs water molecules together
with a combined temperature measurement with a PT100 resistive
temperature sensor.
The DMT345/346 transmitter measures water vapor directly and gives
thus accurate results of moisture in the process. In DMT346 the sensor
is cooled down with a cooling set which makes it possible to use a
polymer sensor in very high temperatures, for example
+100 ... +350 °C. With this technique, no complicated sampling
systems are needed. The cooling set is thermally isolated from the
process itself. The temperature of the sensor is cooled down which
increases the sensor saturation rate.
Sensor saturation rate and temperature are then measured, and the
transmitter calculates the dewpoint and the mixing ratio on the basis
of these readings.
Note that for DMT346, SSR and temperature values don't represent
the process itself as they are measured after cooling. Dewpoint and
mixing ratio, however, are independent of temperature and remain
unchanged.
The dewpoint measurement range is -25 ... +100 °C
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