07.19.12Kelly Duke

Sensor Sensibility – Making Smart Controllers Smart

Lyme Park Mansion The abundant rainfall of The Lake District precludes the need for smart controllers (Shown: Lyme Park Mansion)

I recently wed my long-term girlfriend after some 23 years of extended dating.  We held our ceremony at the Ardbeg distillery on Islay, Scotland (pronounced Eye-lah).  We then stole away for a few days in the Lake District of Northern England.

Some of you may recognize “The Lakes” as the home of Beatrix Potter and the setting of Jane Austen’s beloved social commentary / romance novels.  So for a couple of days, I got to play Mr. Darcy, strolling the grounds of an ersatz Pemberly estate in Ullswater.

As a proper member of the landed gentry, Mr. Darcy did not need to worry about irrigation.  Even if the Lake District did not receive its average of over 80 inches of rain per annum, he could still rely on an abundant staff to manage his estate’s landscaping.

Now back at home in my Southern California digs, I am reminded that water is a fickle, if not a fleeting resource, and that I need to play an active role in its conservation.

We talk a lot about irrigation efficiency and water conservation.  One of the ways that we can achieve both of these goals is by matching water application to the plant, soil, and climate types on a property-by-property (or better yet, zone-by-zone) basis.  One of the more advanced ways of doing this is through the use of  smart controllers.

What Makes a Smart Controller, Smart?

Smart controllers, like people, are only smart because they are well informed.  Keeping a smart controller abreast of the latest environmental data in its world comes down to input from a variety of sensors.  These are generally grouped as follows and described below:

  • Rain
  • Freezing Temperatures
  • Wind
  • Solar Radiation
  • Soil Moisture
  • Irrigation System Flow

Most rain sensors simply interrupt the smart controller’s common wire circuit so as to shut the system down for a few days until the water evaporates from the sensor.  At that time it is assumed that the ground too has dried out and irrigation can return to its normal pre-set routine.  A more sophisticated approach is a “Tipping Bucket rain sensor that actually measures the amount of rain fall so that the data can be incorporated into a smart controller’s overall assessment of its environment for a more accurate application of subsequent irrigation cycles.

Freeze sensors shut down a system when temperatures drop.  This saves water but more importantly prevents plants from damage caused by ice forming on leaves or branches.  It can also prevent ice from forming on pavement and creating a slip hazard from frozen overspray.

Wind sensors (anemometers) are used with more intelligent smart controllers to shut them down when high winds might lead to wasteful wind drift.  Wind sensors are generally part of a suite of sensors rolled into a complete weather station feeding information to the more “Mensa-class” smart controllers.

Solar radiation sensors are one of the more common on-site methods of automatically adjusting controller settings.  Solar radiation sensors can calculate evapotranspiration rates by comparing pre-stored seasonal ET data against real-time field sunlight and temperature measurements.  It uses this data to adjust each station’s program up or down by percentages from a pre-set run-time value.  In contrast to an on-site sensor or weather station, many smart controllers rely upon data input from off-site sensors via internet connections or wireless, subscription-based daily ET data downloads.  The result is the same in that the controller adjusts its in response to the data to conform the irrigation program more closely to true plant needs.

Most simple soil moisture sensors operate like a rain sensor in that they interrupt a normal pre-set and fixed irrigation program until such time as the soil is dry enough to warrant irrigation.  The more sophisticated soil moisture sensors work as part of a holistic smart controller system to dynamically adjust the irrigation program to achieve an optimum moisture level in the soil.

Flow sensors are installed in the system main line at the point of connection.  Flow sensors are used primarily to detect irrigation flows that are outside of normal system programming.  Examples include water flowing when the system is not supposed to be in operation or flow rates that are in excess of an individual zone’s pre-set maximum.  Such events can indicate a broken mainline, a blown-off sprinkler head, or a stuck valve.  In each case, the flow sensor, along with a master valve, shuts the system down.  In many high-end central and web-based controls, the system can even send an alert to the central control computer or by text message to maintenance staff so as to expedite detection and repair of the system upset.

Even today, sensors and their trappings will likely never pierce the bucolic and pastoral beauty of Darcy’s Pemberly estate.  Indeed, the rest of us may even resent that such sensors can make our irrigation controllers smarter than ourselves in matters of water conservation.   However, under the persuasion of our arid southwest, we must overcome our pride and prejudice to embrace them.

Emma right or what?

Kelly Francis, Duke of Pasadena

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Kelly Duke

Not many people can say that they have dedicated their life to the landscape industry. Kelly Duke can. His diverse background ranging from maintenance to estimating, to design, along with a passionate commitment to his trade has given Kelly a lifecycle perspective to landscaping. As the leader of the ValleyCrest’s Pre-Construction Services team, he analyzes early conceptual designs to determine whether or not and how they can be built within budget while meeting long-term design and maintenance goals. Many of the projects that come across Kelly’s desk require he examine the cost and savings of baseline water use in comparison to high efficiency alternatives.




  1. Thursday, 1:26 Caroline Weilert

    What a great post, Kelly.

  2. Thursday, 1:55 Alan Harris

    Oh, how I do enjoy your wit!
    Earlier this week I shared a short story on #landscapechat about a smart controller in the field. The last weather data update was from 2010! The internet connection to download the weather data was via a modem. We hypothesized someone did not recognize the phone number or extension and abandoned the phone line. The solution of the incumbent was to arbitrarily set the irrigation system to run at 110%! We are in the process of getting the smart controller back on line so it can do what it was designed to do…apply the amount of water to the landscape that is required to maintain healthy plants.

  3. Friday, 1:22 Martha Golea

    Kelly, I daresay you’ll have trouble concealing your Renaissance Man status after this post. You make sensors interesting and understandable for the non-irrigation-professionals among us. Thank you!

  4. Friday, 2:16 Kelly Duke

    thank you all for such high praise. Martha: This is especially touching coming from you who I believe to be the “Erma Bombeck” of water management blogs.

    HOWEVER: In the interest of full disclosure my sources suggest that to be a true “Renaissance Man” (or woman) one must meet the following minimum requirements:

    a, Have artistic talent (sculpting, drawing, etchings, cave paintings, acting, etc.)
    b. Be a person of letters (I guess this blog counts)
    c. Be reasonably educated, but more importantly, pass on your knowledge to others
    d. Be involved in civic matters (government, community volunteer, civil defense, local militia, etc.)
    e. Speak at least one foreign language
    f. Play a musical instrument

    While I score reasonably well on a through d, I have failed miserably to learn Spanish or German and equally poorly in attempts at the Violin (4th grad), the Clarinet (5th grade), and more resently, the bagpipes (one key, nine notes, how hard can this be?).

    So while I appreciate your suggestion, I fall well short of Renaissance-ness.

    K. F. Duke

  5. Monday, 1:43 Martha Golea

    Kelly, I stand corrected. I would have thought scoring well on A through D would be good enough, but those Renaissance folks have awfully high standards. I still loved the blog post and you can’t talk me out of that!

  6. Tuesday, 7:42 Randy Barron

    Well-written tutorial on the basic operation and importance of sensor-based controllers, Kelly. Of special importance, and you said it well, is to remember that your controller needs to be well informed. Controllers that adjust programming according to the weather are only as good as the base program that is installed. Don’t set and forget, but monitor for a season to fine tune…

  7. Saturday, 11:16 j price

    This is great news. But someone told that these newfangled contraptions have been around for quite a spell. Sounds like black magic to me. Its like a computer typing machine that tells ya how to spell.

  8. […] station. Information regarding each zone is programmed into the clock so the irrigation schedule is fine tuned daily only to apply as much water as was lost since the last run […]

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