PLC?

My first winter project is on my new high tunnel (greenhouse) High temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process by using a small 12 volt DC gear motor and wench. I've settled on my mechanical design and plan to order parts tomorrow.
My query is on control. KISS is the order of the day here. I plan on two thermostats - Hi and Lo. Also two limit switches - full open and full closed. The control is simple - if you make Hi; roll up for a few seconds and go to delay timer. If you make Lo unroll a few seconds and go to delay timer. Stop on limit switches. Repeat 24X7.
I'm thinking this is PLC territory. I know nothing about them. Is there an inexpensive simple to program unit that runs on 12 volt DC? Alternatively, I can see a way to do it with a timer that continuously does a few seconds on then several minutes off continuously.
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think you'll find you don't need any electronics, at all. Most wenches can think (albeit, just a little) on their own. And all have the requisite strength to open and close a roll-up blind.
If the wench can't do the job, fire her and get another. If you're still not pleased, there are all sorts of tiny PLCs out there with most of the requirements a wench could satisfy.
LLoyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lloyd E. Sponenburgh wrote:

You beat me to it. :-) That sort of spelling just JUMPS out at me for some reason. :-) ...lew...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You should have a field day, then, playing with variations on the idea of Liquid Wench. d8-)
--
Ed Huntress



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 06 Dec 2009 19:52:05 -0600, Lloyd E. Sponenburgh wrote:

You must lead a boring (or very odd) life if most of your requirements for a wench can be satisfied by a PLC!
--
www.wescottdesign.com

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hell! PLC's can cook and clean, and fetch a beer. For the other things, one can find a 'temporary wench'.
LLoyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 07 Dec 2009 09:05:28 -0600, "Lloyd E. Sponenburgh"

Reminds me of the 3F Rule. If it flies, floats, or f----, rent it. Told to my cousin at a dermatologist's conference by an old thrice divorced attendee.
Pete Keillor
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
There are some of the little (micro, Pico, Nano) PLC's that have a LCD display and some keys used for configuration. That way you don't need to get programming software, cables, etc.
http://www.softwarecorp.com/FX2N14.htm
http://www.ab.com/programmablecontrol/plc/pico/controller.html
http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_%28Micro_to_Small,_Brick_-a-_Modular%29/DirectLogic_05_%28Micro_Brick_PLC%29/PLC_Units/D0-05DR-D
The Automation Direct PLC looks like it would take programming software and cable.
You can get a couple of 12VDC relays to control your gear motor.
RogerN
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_%28Micro_to_Small,_Brick_-a-_Modular%29/DirectLogic_05_%28Micro_Brick_PLC%29/PLC_Units/D0-05DR-D

I like the price of this one best, its the cheapest. And, Automation Direct has always been good to me. I see the software is free for 100 words max. I have no clue, would this be enough for my application? Room to spare?
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm thinking it would. Download the manual and start coding. The documentation should tell you how to count the words you are using.
You might want to look here: http://www.bb-elec.com/product_multi_family.asp?MultiFamilyId9&Trail 8&TrailType=Main
I never got a chance to use one since I the thing I needed done was easy enough to wire up using dicrete relays but it was looking like quite a deal at the time.
Wes
--
"Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Running Light
without
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_%28Micro_to_Small,_Brick_-a-_Modular%29/DirectLogic_05_%28Micro_Brick_PLC%29/PLC_Units/D0-05DR-D
I think it would be plenty, not sure if they consider each bit instruction as a word or not.
You want open for a couple of seconds if not on open limit and high temp.
You want close for a couple of seconds in not close limit and low temp.
Another timer could reset the open and close timers if still hot/cold after XX minutes. Maybe if it's hot, opened for a couple of seconds, maybe 15 minutes later if it's still hot open for a couple more seconds.
I'm sure you could get it going in less than 100 words, probably in less than 20 words.
Some of those other PLC's had analog inputs. If you were to use a temperature sensor to an analog input you wouldn't need the thermostats. A thermistor could possibly be used but may need an amplifier to get better resolution.
RogerN
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_%28Micro_to_Small,_Brick_-a-_Modular%29/DirectLogic_05_%28Micro_Brick_PLC%29/PLC_Units/D0-05DR-D
Also worth a mention, the more expensive ones have the display and keypad built in. That could be handy for modifying the timers for open/close jog times. With the Automation Direct software you can make the changes but you would have to use a PC. .. Unless you programmed it to change time based on jumpering spare inputs, maybe using spare outputs as indicators.
RogerN
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hey Karl,
A local farmer here won an award very recently for his "high tunnel greenhouse" farming, and here you are doing the same stuff. Local media didn't attempt to explain what is special about it. We buy "retail" from their farm, and I don't see anything different about either the crop or the greenhouses they have, other than maybe an extended season. Lots of agriculture around here under plastic "glass", maybe several hundred acres. Not as much as in the Leamington area, known as the Ontario Sun Belt, where that would be in the thousands of acres I would think. So, in a few short words, can you tell me what a "high tunnel greenhouse" is, and why it is special anyway?
Take care.
Brian Lawson, Bothwell, Ontario.
ps....lot's of older and "NOS" PLCs available on the internet auctions to try. I'd like to give some a go, but the availability of the programmers required is not so easy to find at "that looks like fun" prices.
XXXXXXXXXXXXXXXXXXXX
On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Think simple greenhouse exept $/sq.ft. must be lower. Usually no to limited electric. Most important crops are planted in soil. The aim is to produce a crop such as tomato, etc. that harvests much earlier in the season.
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 7 Dec 2009 10:09:26 -0600, "Karl Townsend"

Yabbut what's the difference between "High tunnel" and plain ordinary polytunnel greenhouses?
Expiring minds want to know :-)
Mark Rand RTFM
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

If you're looking at the structure the difference is blurred. Few greenhouses use natural ventilation - large exhaust fans. most high tunnel have huge natural vent opening.
The main difference is application. Greenhouse grow plant for resale in some sort of medium normally on shelves. High tunnel grows fruit and vegetables in the soil.
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 8 Dec 2009 20:54:22 -0600, "Karl Townsend"

Ok, That's what I'd know as polytunnels (not the same as the home vegetable plot variety though...)
regards Mark Rand RTFM
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 08 Dec 2009 23:47:38 +0000, the infamous Mark Rand

Who cares? With your feared AGWK, you'll soon be able to grow tomatoes Over There, too!
-- To know what you prefer instead of humbly saying Amen to what the world tells you you ought to prefer, is to have kept your soul alive. -- Robert Louis Stevenson
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"
<snip>

<snip> For some ideas [and to avoid reinventing the wheel] see http://www.gavishusa.com / http://www.pc-control.co.uk/actuators.htm http://www.pc-control.co.uk / http://www.actahort.org/members/showpdf?booknrarnr 4_47 http://www.actahort.org/books/87/87_28.htm http://www.dpi.nsw.gov.au/agriculture/horticulture/greenhouse/structures/computer-control http://www.globalgreenhousesystems.com /
google on <greenhouse OR hydroponics "computer control"> for c. 21k hits.
also see http://computer1.software.informer.com/download-computer-control-hydroponics-monitoring / http://www.cropking.com/index.shtml?ref=google&gclid=CO_O7dbTxJ4CFQ_xDAod9RqDpA http://www.cropking.com/commercial
http://www.agriculture.purdue.edu/aganswers/story.asp?storyIDE57 http://www.icarda.org/Publications/HorticultureResearchatICARDA.pdf http://www.cgiar.org/pdf/cp_cn_highvaluecrops.pdf http://www.cgiar.org/pdf/agm07/agm07_cp_highvalue_crops.pdf http://www.countryroads.net/agjournal/linklist.cfm?section 
Please let the group know how things work out.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for all the links. I surfed them and they all seem to violate KISS and cost too much. I've been surfing the web for days on this subject and just came from a growers conference. Nobody (growers) there was using automatic ventilation except the university types.
So far the simplest unit I found costs $700 each (need four per house) and fails if 110 Volt isn't there. I got the mechanical part designed at under $50 per unit that would run days on a deep cycle battery. Control is my weak subject so I'll spend way more time figuring on this.
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.