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OVERVIEW
Rain Sensors will shut down your lawn sprinkler system after sufficient rainfall has been detected.
It is important to note that a rain sensor will not shut down a sprinkler system simply because it has started raining; sufficient rainfall must be detected before the rain sensor will shut down the sprinkler system.
Rain sensors must be mounted where normal rainfall occurs.
This means you do not want to mount the rain sensor where it is shielded from rainfall or where an abnormal amount of rainfall is re-directed into the sensor.
The most common style of rain sensor is one that uses special fabric discs to collect rain drops.
These fabric discs expand when they get wet and press a micro-switch when sufficient rainfall is detected.
The main advantage of this style over a rain sensor that collects rain in a cup is that the fabric discs dry out at the same rate as your lawn does.
Cup style rain sensors can take much longer for the water to evaporate out of the cup.
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Rain Sensor Types and Wiring
There are two main types of rain sensors: Normally Open and Normally Closed.
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Normally Closed: In this type of rain sensor the switch is normally closed.
Normally Closed rain sensors are wired in series with the common ground wire.
Specifically said, the common ground wire(s) from your control valves is/are connected to one rain sensor wire and the other rain sensor wire is connected to the common ground terminal in your timer.
When sufficient rainfall is detected, the switch opens and
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After Rain
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temporarily breaks the electrical circuit.
Your timer will continue to operate and it appear as if sprinklers should be watering.
However, since the electrical circuit is temporarily "broken" the timer will not be able to open any valves until the rain sensor dries out and completes the electrical circuit.
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Normally Open: In this type of rain sensor the switch is normally open.
Normally Open rain sensors are wired directly to special rain sensor terminals in your timer.
When sufficient rainfall is detected, the switch closes which completes an electrical circuit.
Your timer senses the newly completed circuit and disables the automatic program until the rain sensor dries out and the electrical circuit is broken.
Your timer should display an icon or warning light when the rain sensor is disabling
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the system.
Some timers will have a built-in override feature in case you want to by-pass the rain sensor.
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Rain Sensor Adjustments
Most rain sensors have an adjustment for sensitivity.
This adjustment is usually a mechanical adjustment that affects the amount of rain required to trip the sensor's switch.
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Other Types of Sensors
Rain sensors are not the only type of sprinkler system shutoff switch available.
There are sensors for high winds, freezing conditions, and even one for soil moisture content.
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©2003 Pioneer Midwest Inc.
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