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Vaisala's DRD11A Rain Detector offers fast and accurate precipitation detection (ON/OFF). It operates on the basis of droplet detection, rather than signal level threshold. The capacitive principle utilizes the RainCap sensor plate. A special delay circuitry allows about a two-minute interval between raindrops before assuming an OFF (no rain) state. The means the sensor can accurately distinguish between rain cessation and light rain.
The sensor also features an analog rain signal for estimating rain intensity. The default rain categories of the estimated intensity are: low, moderate and heavy rain. An internal heating element is provided to ensure that the detection surface dries quickly. The same element also protects the surface from fog and condensed moisture. It is activated at low temperatures in order to melt snow, thus enabling snow detection as well.
Vaisala's multi-variable present weather instruments, the FD12P and PWD11, combine Vaisala's forward-scatter visibility measurement and RainCap capacitive rain detection technology. These sensors detect precipitation type, measure precipitation intensity, calculate precipitation accumulation, and also calculate the water equivalent of frozen precipitation and snow accumulation.
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