Re: RE: greenhouse-tomatoes: Want to automatically trigger irrigation cycles

["richard" <richard@intertechserv.com>]

greenhouse-tomatoes - an email list for growers of greenhouse tomatoes.
Sent by "richard" <richard@intertechserv.com>.
-

If you buy the rain sensor from rainbird you can modify it to serve this
purpose.  Get the one that mounts on the house roof and has a collection pan
with 2 probes to measure the water height.  I first used this method in
1986.
If you can not find it I still have one or more in stock.

Richard Gerhart, International Technology Services Inc
richard@intertechserv.com
303-661-9546
303-661-9543 FAX

----- Original Message ----- 
From: "ronald polka" <rpolka@nmsu.edu>
To: <greenhouse-tomatoes@Lists.MsState.Edu>
Sent: Thursday, June 10, 2004 5:14 PM
Subject: Re: RE: greenhouse-tomatoes: Want to automatically trigger
irrigation cycles


> greenhouse-tomatoes - an email list for growers of greenhouse tomatoes.
> Sent by ronald polka <rpolka@nmsu.edu>.
> -
>
> 6/10/2004 10:59:29 AM, "Eng, Doug MSER:EX" <Doug.Eng@gems3.gov.bc.ca>
wrote:
>
> >greenhouse-tomatoes - an email list for growers of greenhouse tomatoes.
> >Sent by "Eng, Doug MSER:EX" <Doug.Eng@gems3.gov.bc.ca>.
> >-
> I am looking for a way to trigger irrigation cycles based on tomato plant
> need.
>
>
> Doug
> An alternative to triggering irrigation cycles based on tomato plant needs
is to stop preset
> irrigation intervals based on the presence of leachate at a sampling
location. I assume your intention is
> to limit the irrigation cycle so as to conserve water and nutrients. If
so, then a relatively straight
> forward method is to monitor for the presence of leachate and disconnect
you power to the pump when
> leachate is detected. You can keep your present method of initiating
irrigation cycles with the timers,
> they are a generally reliable method of watering at preset times.
> At one or more locations in the greenhouse a leachate collection pan or
container needs to be setup
> so it fills a sample container upon leaching from the pot. A liquid sensor
is then installed in the
> leachate collection container and is wired to the coil side of a relay
that will disconnect the power to
> the pump when the liquid sensor electrodes are immersed in the leachate
thus signaling the presence of
> leachate.
> Some experimentation is required to achieve the correct timing sequence of
the events in this
> control strategy. For example you know the approximate time required for
leachate to appear under average
> conditions, then add however much additional time you want for leaching to
occur. This sum is an average
> on-time for your pump. Then pick a theoretical maximum on time for your
pump. The time difference is the
> window that the pump controller must work on. For example suppose you have
an average pump-on time of 5
> minutes, 4 minutes watering plus 1 minute of leaching. And you don't
anticipate a pump on-time to exceed
> 10 minutes under the most adverse conditions. Your pump on-time timers can
be set to operate for 10
> minutes on and the pump controller can handle the last 5 minutes of the
cycle. The leachate container must
> be constructed to drain below the controller electrodes after the timer
cycle ends but before the next
> pump on-time cycle begins. For example if you have watering cycles every 2
hours then the leachate
> container needs to be dry before then. Otherwise the pump will not turn on
when the timer completes the
> circuit. A small container with a tiny hole may suffice or you can
experiment with various types of wicks.
> The liquid controller is a handmade circuit board of various electronic
components. A working
> knowledge of electronic circuits is necessary for its construction but its
not rocket science. There are a
> number of workable schematics available on the web. One excellant one that
I have used is available at the
> following address. http://www.uoguelph.ca/~antoon/circ/sensor3.htm
> This is a very good circuit for this application because the AC signal
across the electrodes prevents
> electrode corrosion in the nutrient solution. The small relay in the
circuit can be used to drive a larger
> double throw relay that will turn off pump power when the electrodes are
immersed in the nutrient.
> Multiple sensors can be used and wired in parallel.
> I have not used this circuit in this particular application, I use a timer
in a closed system and
> reuse nutrient. But I have used it successfully to control make up water
cycles on solar water
> distillation units utilizing a very similar strategy to the one outlined
above. If you are interested in
> this type of control and need additional information let me know.
> Best of luck.   Ron
>
>
> >
> Ron Polka
> Southwest Technology Development Institute
> New Mexico State University
> Box 30001, Dept 3SOL
> Las Cruces
> NM 88003
> 505 646-5434
> Fax 505 646-2960
> email rpolka@nmsu.edu
>
>
>
>