Which Watering Timer Is Right For You?
A rain sensor will shut down your watering system after sufficient rainfall has been detected. It is important to note that a rain sensor will not shut down a watering system simply because it has started raining: sufficient rainfall must be detected before the rain sensor will shut down the watering system. |
Rain sensors for your garden are simple and easy to install. 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 discs shrink as they dry, until they release from the electrical switch, restoring the normal cycle of your irrigation system.
The other rain sensors on the market use a water collection dish, tipping bucket or probe to detect rainfall via water weight or electrical conductivity. Rain sensors measuring water weight or conductivity main require more maintenance to remove dirt and debris which can alter the weight or foul the device.
The main advantage of sensor which uses discs 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 to evaporate out of the cup.
Rain sensors with expansion discs are the most popular type because they are highly reliable and require little maintenance.
Whichever sensor is used, it will temporarily interrupt the automatic watering system’s programmed cycle until the detection device dries out. One to several days after the rainfall, the automatic timer will come back on line and its regular schedule will resume.