Vaisala WXT510 - Manual (Page 25)

Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 23
Precipitation Measurement Principle
WXT510 uses Vaisala RAINCAP
®
Sensor 2-technology in
precipitation measurement.
The precipitation sensor comprises of a steel cover and a piezoelectrical
sensor mounted on the bottom surface of the cover.
The precipitation sensor detects the impact of individual raindrops. The
signals from the impact are proportional to the volume of the drops.
Hence, the signal of each drop can be converted directly to accumulated
rainfall. Advanced noise filtering technique is used to filter out signals
originating from other sources than raindrops.
The measured parameters are accumulated rainfall, rain current and
peak intensity, and the duration of a rain event. Detection of each
individual drop enables computing of rain amount and intensity with
high resolution. Precipitation current intensity internally updated every
10 seconds represents the intensity during the one minute period minute
before requesting/automatic precipitation message sending (for fast
reacting 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 fixed one minute). Precipitation peak intensity represents the
maximum of the calculated current intensity values since last
precipitation intensity reset.
The sensor is also capable of distinguishing hails from raindrops. The
measured hail parameters are cumulative amount of hails, current and
peak hail intensity and the duration of a hail shower.
The precipitation sensor operates in the following four modes:
- Precipitation Start/End mode:
Transmitter sends automatically a precipitation message 10
seconds after the recognition of the first drop. The messages are
sent continuously as the precipitation proceeds and stopped 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).