Precipitation current intensity is internally updated every 10 seconds and represents the
int
ensity during the one minute period before requesting/automatic precipitation message
sending (for fast reactions to a rain event, during the first minute of the rain event, the
intensity is calculated over the period rain has lasted in 10-second steps instead of a fixed
period of one minute). Precipitation peak intensity represents the maximum of the
calculated current intensity values since last precipitation intensity reset.
The sensor can also distinguish hail stones from raindrops. The measured hail parameters
are the cumulative number of hail stones, current and peak hail intensity and the duration of
a hail shower.
The precipitation sensor operates in four modes:
• Precipitation Start/End mode:
Transmitter automatically sends a precipitation message 10 seconds after the
recognition of the first drop. The messages are sent continuously as the precipitation
pr
oc
eeds and stop when the precipitation ends.
• Tipping bucket mode:
This mode emulates tipping bucket type precipitation sensors. Transmitter sends
automatically a precipitation message when the counter detects one unit increment
(0.1 mm/0.01 in).
• Time mode:
Transmitter sends automatically a precipitation message in the update intervals defined
by the user.
• P
olled mode:
Transmitter sends a precipitation message whenever requested by the user.
More Information
‣
Precipitation Sensor (page 127)
3.3 PTU Measurement Principle
WXT536 WXT535 WXT534 WXT533 WXT532 WXT531
✔ ✔ ✔
The PTU module contains separate sensors for pressure, temperature, and humidity
measuremen
t.
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.
Chapter 3 – Functional Description
29
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www.streamlinemeasurement.co.uk
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