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  • ET Script

    I plan to use a script that I found here >> http://forums.homeseer.com/showthread.php?t=138704 to gather data from my Davis Weather System.

    I would also like to use the ET value for controlling my sprinklers. I have the solar radiation sensor on my system so I do have the ET values.

    My 24 zone sprinkler system is now controlled by my JDS Stargate and I keep track of the last six days of rain bucket tips to control my "rain delay" flag which simply cancels the schedule until the flag clears. I also use temperature measurements to modify the schedule.

    Instead of my existing crude method, I would like to incorporate ET control with a HS script that would set a flag that the Stargate could read to set/clear the rain delay flag.

    What values of ET should be used for this.

  • #2
    The mcsSprinklers approach is keep track of the moisture content in the soil based upon the ET and rainfall amounts. When a user-defined soil dryness level is reached then the irrigation cycle is run and the soil moisture adjusted to reflect the moisture that has been added during the irrigation cycle.

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    • #3
      Thanks for the reply.

      Could you share the formula that you use?

      I don't want to dump the reliable system that I have. I have 15 years invested in it's development and it all works great. I just want to improve it by adding ET into schedule control.

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      • #4
        mcsSprinklers does the computation hourly, but you could do it daily as well. You have some staring moisture level, say 1 inch. At the end of the day the ET reflects 0.2" moisture loss. The rain gauge indicates 0.1 inches of rainfall. The soil moisture at the start of the next day will be 1.0 - 0.2 + 0.1 = 0.9. You have selected to irrigate when when the soil moisture is at 0.3 inches so with it at 0.9 you skip the irrigation cycle for the day.

        At some future day the moisture will calculate to be under 0.3 so for that day you run the irrigation cycle. After the irrigation cycle is complete then your soil moisture will be back to 1" or whatever level you have added based upon how long you run the valve and the flow rate of the valve.

        Another approach is to maintain moisture lost. In the example above after the first day you have lost 0.1" of moisture so you schedule the day's irrigation cycle to run sufficiently long to replenish 0.1 inches. Again you can change the interval from daily to weekly as an example so you will add up the daily ET for 7 days, less the rainfall and then run the irrigation cycle once during that week to replenish that level of moisture.

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        • #5
          Good, thanks. This is what I needed to get a start on this.

          I think I will collect data this summer and run tests on my zones again to measure how much water is actually being delivered and then introduce ET into my system.

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