Precipitation measurement principle - WXT530

WXT530 Series User Guide

Document code
M211840EN
Revision
F
Language
English (United States)
Product
WXT530
Document type
User guide
WXT536 WXT535 WXT534 WXT533 WXT532 WXT531

The transmitter 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. The signal of each drop can be converted directly to accumulated rainfall. An advanced noise filtering technique filters out signals originating from other sources than raindrops.

The measured parameters are:

  • Accumulated rainfall
  • Rain current and peak intensity
  • Duration of a rain event

Detecting each drop enables the computing of rain amount and intensity with high resolution.

Precipitation current intensity is internally updated every 10 seconds and represents the intensity during the 1-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 1 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 4 modes.

Table 1. Precipitation sensor modes
Mode Description
Precipitation start/end mode The transmitter automatically sends a precipitation message 10 seconds after the recognition of the first drop. The messages are sent continuously and they stop when the precipitation ends.
Tipping bucket mode The mode emulates tipping bucket type precipitation sensors. The transmitter sends automatically a precipitation message when the counter detects 1 unit increment (0.1 mm/0.01 in).
Time mode The transmitter sends automatically a precipitation message in the update intervals defined by the user.
Polled mode The transmitter sends a precipitation message when requested by the user.