Vaisala WXT532 - PTU Measurement Principle; Heating

User’s Guide ______________________________________________________________________
34 __________________________________________________________________ M211840EN-C
PTU Measurement Principle
The PTU module contains separate sensors for pressure, temperature,
and humidity measurement.
The measurement principle of the transmitter is based on an advanced
RC oscillator and two reference capacitors against which the
capacitance of the sensors is continuously measured. The
microprocessor of the transmitter performs compensation for the
temperature dependency of the pressure and humidity sensors.
The PTU module includes
- Capacitive silicon BAROCAP sensor for pressure measurement,
- Capacitive ceramic THERMOCAP sensor for air temperature
measurement
- Capacitive thin film polymer HUMICAP180 sensor for humidity
measurement.
Heating
The heating elements located below the precipitation sensor and inside
the wind transducers help keeping the sensors clean from snow and ice.
A heating temperature sensor (Th) underneath the precipitation sensor
controls the heating. Note that Th is measured inside the equipment,
where temperature is much higher than the ambient temperature (Ta).
WXT536 WXT535 WXT534 WXT533 WXT532 WXT531
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WXT536 WXT535 WXT534 WXT533 WXT532 WXT531
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NOTE
When operating the sensor in temperatures below 0 °C (32 °F), select
a model with an internal heater and enable the heater for operation.