A rain water detector, or rain sensor, typically works by detecting the conductivity of water bridging a gap between conductive elements.
Here's a breakdown of how it works:
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The Sensing Element: The core of the detector is a sensor surface, often made of a non-conductive material like mica or Bakelite. This surface is interlaced with conductive tracks, typically made of aluminum or another metal. These tracks are designed to be close together but not touching when dry.
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Detection Principle: Conductivity: When rain falls on the sensor, water droplets bridge the gap between the conductive tracks. Water, even relatively pure rainwater, contains dissolved minerals and impurities that make it conductive.
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Completing the Circuit: The water bridging the gap completes an electrical circuit. A small voltage is applied across the conductive tracks. When water is present, current flows through the water, indicating rainfall.
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Resistance and Measurement: The amount of current that flows is related to the amount of water on the sensor. The resistance between the conductive tracks decreases as more water is present. The sensor circuit measures this resistance change.
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Signal Output: The change in resistance, and therefore the current flow, is converted into a signal that can be used by other devices. This signal can trigger an alarm, close a window, stop irrigation systems, or perform other actions.
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Example Scenario: Imagine the sensor connected to an automatic irrigation system. When the rain sensor detects rain, the signal is sent to the irrigation controller, which then shuts off the sprinklers to avoid overwatering.
In summary, a rain water detector leverages the electrical conductivity of rainwater to complete a circuit and signal the presence of rain. The change in resistance across the sensor indicates the presence and often the intensity of the rainfall.
