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Making Sense of Sensing Devices

DANNY FASOLD | Landscape Maintenance

WATER, WATER EVERYWHERE—IT might seem that way, since much of our earth is covered in water, but we all know that water is an exhaustible resource and we must do our part to conserve.

Besides, no one likes to be wasteful. You wouldn’t let your air conditioning system blast away all day. Instead, you’d use a thermostat to determine when the temperature is hot enough to the point where it calls for the air conditioning to be turned on. This way, you’re cooling the house only when necessary.

Likewise, you wouldn’t want to leave your irrigation systems on all day. Can you imagine all the damage that would inflict on the plants? How much water runoff that would create? Many homeowners will let their irrigation systems run on simple timers and have them go off at certain times of the day, but this isn’t a very practical way to irrigate. After all, what if it happens to be raining when the controller tells the system to irrigate? Consequently, you’d be watering turf that’s already had all the water it needs.

This is why sensing devices are so beneficial. Just as an air conditioning system will turn on only when the thermostat tells it to, sensing devices can allow irrigation systems to start and stop according to certain environmental conditions.

“There’s a very thin line between over-watering and under-watering,” says Tom Penning, president of the Irrometer Company, Riverside, California. “If there’s not enough water, the plant has to work that much harder to extract what’s left. But you can’t saturate it all the time because you have to get air to its roots as well. Sensing devices make it easier to manage between those two points.”

There are two main types of sensing devices used in the irrigation industry today: Rain sensors and soil moisture sensors. Rain sensors measure the number of inches of rain that have fallen onto the surface of the site, whereas soil moisture sensors are buried in the ground and measure the moisture content of the soil. Their purpose, like the thermostat, is to make sure that the system doesn’t water when it’s not necessary (i.e., when it’s raining).

Offering sensing devices to your clients can be a great way to set yourself apart from the competitors and gain a leg up. Your clients will be happy as well. After all, they’ll stand to save anywhere from 30 to 40 percent of the amount of water they would normally use. And they’ll also have the satisfaction of knowing they’re living the green lifestyle.

In some parts of the country, water agencies are offering incentives for installing sensing devices.

These incentives are available in Northern California, Florida, Georgia and the Carolinas. Some states, such as Texas and New Jersey, are even requiring that rain sensors be included in irrigation systems.

But make no mistake: sensing devices have a long way to go. Many people aren’t using them, either for lack of awareness or due to a general aversion to the technology. Soil moisture sensors have somewhat of a stigma attached to them because some of the early devices from years ago were poorly designed and faulty. As a result, some contractors still refuse to use them. Technology has improved tremendously in recent years, however, and today soil moisture sensors lead the vanguard of smart water technology.

“There are a lot of people out there looking for ways to save on water, but they don’t know where to look,” claims Kevin Holderness, vice president of Acclima, Meridian, Idaho. “They can lick their finger and stick it up in the air, or they could stick a sensing device on their site. Which do you think will be more effective?” If you’re wondering how reliable sensing devices are, or how they work, this article will certainly help you. It’s time to put aside your fears and skepticism, and take advantage of this exciting technology.

Rain sensors

Although rain sensors and soil moisture sensors both adjust run-times based on the amount of rainwater on-site, they’re really quite different. Rain sensors, as stated earlier, register the number of inches of rainwater that has fallen on a site. Users can program these sensors so that when a certain amount of rainfall has fallen (say, one inch) the sensor will send a signal back to the central controller telling it to stop watering the turf. The controller will then immediately stop irrigating, so as not to over-water.

One of the early rain sensors was the Mini Clik from Hunter Industries. It opened the market for these devices when a few municipalities mandated they be installed.

Contractors have two choices in the type of rain sensor they want. One type is generally referred to as a “tipping bucket.” This kind of rain sensor basically acts as a catch-can, catching rainwater as it falls and stores it in a tiny catch basin. Once the water reaches a designated height, it will tell the controller to stop irrigating.

“Tipping rain buckets allow you to measure how much rain falls, usually in increments of one-tenth of an inch,” explains Brian Ries, marketing manager for The Toro Company’s Irrigation Division in Riverside, California. “These sensors can automatically adjust the controller to cancel irrigation during a rain event. Some of the higher-end systems will actually pause while it’s raining to wait and see how much rainfall occurs before it decides to cancel or continue watering.”

The other choice is called a “switch sensor.” This device uses a hydroscopic disc made up of a material similar to that which you’ll find in cork. As this disc comes into contact with rainwater, it will start to expand. If the disc gets wet enough, it will expand to the point where it releases a switch which will shut off irrigation. When the disc dries, it will shrink and release the switch, turning the system back on.

Soil moisture sensors

There are a number of different types of soil moisture systems which work in different ways, but all of them have the same end result: they are able to give the controller accurate estimates on how much water has been absorbed by the soil.

Soil moisture sensors work by measuring how much electricity can pass through the soil. Water is conducive to electricity, thus, the larger the electrical charge being emitted, the greater the moisture content.

Different soil moisture sensing devices will study electrical charges in different ways. For instance, analog devices will study the time it takes for an electrical discharge to travel along the site. Companies such as Acclima, on the other hand, use digital technology to take digital photographs of electromagnetic waves in addition to studying the time it takes for that wave to travel. This gives users even more accurate readings of soil moisture content.

These devices have been around for many decades, but in their time, they’ve been plagued by a number of problems. Early soil moisture sensors would often deteriorate shortly after they were installed in the ground, as the acidic properties of the soil would cause the metal to degrade.

They were also vulnerable to electrical surges. Lightning strikes would destroy the devices.

Early devices also ran the risk of altering the properties of the soil because of the electrical activity. This would make it more difficult for the sensors to give accurate soil moisture measurements.

But as we all know, technology has a way of improving. Today, soil moisture sensors are typically made of noncorrosive materials such as ABS plastic, stainless steel or PVC-jacketed wiring. Some moisture sensors will encase their electrical components in a granular matrix made of gypsum and chalk, which helps prevent them from altering the soil, while companies such as Irrometer won’t place any electrical components in the ground whatsoever, relying on electrodes instead.

“If a contractor got a bad taste in his mouth from using older soil moisture sensors, he should try it again using a different product,” says Penning. “The technology is leaps and bounds from where it once was, and to never use the technology again because of one bad experience—that’s a bit shortsighted, I think.”

According to Holderness, “Comparing the old technology to the new technology is like comparing skateboards to rocket ships. Things are so far advanced with moisture sensors that there really is no comparison. If someone grumbles, ‘Oh, well, I tried that before and it didn’t work,’ then they should look to a different brand.”

Hand-in-hand

Just like with most any product, there are drawbacks to these devices. Rain sensors are limited in that they only tell the irrigation system to shut off when it’s raining. It doesn’t factor in how much water is actually getting absorbed by the soil or how long the soil stays saturated.

“Rain sensors aren’t looking at how you should apply water to get the healthiest, most beautiful plants,” explains Jon Peters, director of sales as Baseline Inc., Boise, Idaho. “Once it’s stopped raining, the controller will resume its normal run-times, regardless of whether or not the soil needs water. If you rely only on these sensors, you still run a high risk of overwatering.”

Likewise, if you rely only on soil moisture sensors, the risk of over-watering is equally high because they won’t turn off the irrigation system until they’ve detected a high enough soil moisture content. “Moisture sensors respond a lag behind the rain sensor,” explains Brian Mueller, senior product manager for Rain Bird, Tucson, Arizona. “A rain sensor will catch rain immediately, but because moisture sensors are buried, they have to wait for the water to percolate into the root zone of the ground.”

The best strategy is to install both sensing devices on the same site so that they work together in a closed loop system. This way, the irrigation system waters the property only when necessary.

“By working in concert with one another, a closed loop system of moisture sensors and rain sensors will give you the healthiest turf and conserve the most water,” says Mueller.

An evolving technology

Sensing devices are not limited to just moisture sensors and rain sensors. There are weather stations as well, which are comprised of several sensors which gauge certain environmental factors. These sensors include thermometers, solar sensors, wind sensors and even rain sensors.

“Weather stations put a numerical value on each data point for each sensor, such as temperature, humidity, wind and so on,” says Peters. “It will then calculate the appropriate run-times.”

CalSense, based out of Carlsbad, California, offers its own unique sensor. This tipping rain bucket device will collect rainfall and stop irrigation after a certain number of inches of rain has fallen, just as a traditional rain sensor would. However, this device takes it two steps further by logging the maximum amount of rain for each hour as well as helping to determine the holding capacity of the soil.

“The difference between our product and a rain sensor is that this allows our controller to determine how much of the rainfall is usable for the soil,” explains Rick Capitanio, vice president of CalSense. “This will help us to know when to turn the controller back on once the usable rainfall is gone.”

There’s also a subset of rain sensors which are beginning to make a big splash on the market. These special rain sensors feature a rain/freeze capability, that prevents irrigation once the temperature drops to a freezing level. Says Ries, “If you irrigate during freeze conditions, you can cause damage to the irrigation system. Frozen water can cause the pipes to crack, or you can create ice on the property, causing further hazards. It’s also very difficult for water to penetrate the soil when it’s freezing.” This feature is already required for certain regions in Texas.

The Toro Company offers a feature with its rain sensors called Water Conservation Mode, which intelligently extends the reset time of the irrigation system based on how long the rain sensor was exposed to rain. “Because they’re installed above ground, rain sensors are exposed to a lot of sun and wind, and oftentimes dry out much faster than the soil does,” explains Ries. “Our Water Conservation Mode will extend the time before it resets the run-times so it saves more water in the end.”

Sensing devices have come a long way. As the cost of water is more of an issue than ever before, the use of sensing devices makes sense. If you want to be a good steward for water conservation, now is the time to look at these technologies to see what you can do to help save water.

 
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