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Incorrect and correct ways to wire dual sensors (i.e., rain shut-off and soil moisture)


Wiring dual sensors: Rain shut-off (RSD) + Soil moisture sensor (SMS)


Before: Both sensors were wired directly into single sensor port. This did not allow the sensors to work properly.


Why? If one sensor says “bypass” but the other says “allow,” the signal could still travel a complete loop, and a scheduled irrigation cycle would still occur. Before


Watering Watering Watering allowed


allowed


RSD allow allow SMS


allowed bypass allow bypass allow Bypassed bypass bypass ---------------------------------------------------------------------------------------------


After: Sensors are now wired together “in series.” The signal must travel a single complete loop through BOTH sensors. This allows either sensor to bypass an irrigation cycle.


Example: If one sensor was in “bypass” but the other was in “allow,” the signal could NOT travel a complete loop, and a scheduled irrigation cycle would be successfully bypassed.


Watering allowed


After Bypassed Bypassed Bypassed


RSD


SMS


RSD


SMS


RSD


SMS Photo credit: Francis Galdo, water conservation and efficiency coordinator at Pasco County Utilities


are several irrigation events scheduled per week, that means everything has to line up perfectly, which isn’t likely. The benefits to adding a rain sensor are probably marginal because they also require more maintenance. “You’re adding something that needs more maintenance for some perceived benefit, which is not all that great,” Dukes said.


Perception vs. Reality


When it comes to water savings and homeowners, Dukes said, “Perception is reality.” Surveys of homeowners involved in an Orange County Utilities research study showed that their perception of water savings was more important than the actual water savings in their attitude of whether they were going to continue using smart irrigation technology in the future.


Having a rain sensor to prevent a system from running when it’s raining contributes significantly toward perception. Having a system with only a soil moisture sensor is probably not a real problem in the long run, day in and day out, throughout the year. But if a developer sees a system watering in the rain one time, it may mean the difference between these new homes continuing to get this technology or not getting it.


Parallel vs. In Series


The problem with the new housing development arose when something went wrong with two sensors connected to one timer. In this situation, the timers had a rain sensor port, and the


installers wired both sensors to that port. They intended an either/ or scenario to interrupt irrigation. But, when both are wired in this way they are in parallel, so both have to trigger to interrupt irrigation. They needed to be wired in series so either/or would break the circuit.


Dukes offered the following advice for those insisting on using both a rain sensor and soil moisture sensor with a timer: “Know your wiring.”


Michael Dukes, PhD, PE, CID, is a professor and irrigation specialist in the Agricultural and Biological Engineering Department at the University of Florida and director of the Center for Landscape Conservation and Ecology. He and his


team conduct research and education on topics related to efficient irrigation and water conservation in landscapes.


Michael Gutierrez is a water resources


technician and digital media specialist with UF/IFAS in the Agricultural and Biological Engineering Department. When he's not maintaining/training others on smart irrigation devices, he's shooting video of someone who is and tweeting about it.


irrigationtoday.org 19


RSD


SMS


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