A Community and Forum For Aquaponic Gardeners

PLC-based Control Box

I've been gradually building a control box for my home aquaponics system. It's clearly un-necessary, but I'm using it as a test bed to prepare for use in greenhouse and larger scale operations. I also want to measure various things long-term. I'm definitely taking the industrial control approach, but I think it's appropriate given the potentially harsh conditions of a greenhouse, and the potential value/risk of thousands of gallons of water and fish and produce. I definitely think these systems can be designed to be mostly passively safe and reliable (without controls), and there is clearly a breaking point below which an investment like this makes no sense. Nonetheless, I carry on for the fun of it :)

I have much of it up and running, but still have most of the operational logic to develop still. Early photo attached. More as I get things hooked up. One part I haven't completed is hooking up graphical screens on the laptop to the PLC. One big advantage of a PLC is that it can take care of all the critical functions without any attached PC or laptop. Adding the laptop just means I can graphically monitor the system, perform manual functions, and log data to disk. I'll be using an open-source control system called EPICS for that. More later. A parts list for the box follows the photo:

Parts:

1 Wiegmann NEMA 3R electrical enclosure - $90
DIN rails - $10
2 Solid State 10A Relays - $40
24V power supply $30
Terminal blocks - $20
Used Koyo DirectLogic06 PLC from Ebay - $130
RTD temperature sensor card for PLC - $199
4-20mA input card for PLC - $79
2 RTD temperature sensors - $100
2 float switch sensors - $20
Furman MP-15 relay-controllable 110V outlet - $100
Used laptop from Ebay - $125 (PLC programming software free for small programs)
Relay controllable ASF-1 fish feeder - $79
4-20mA pH sensor transmitter - $189
submersible pH sensor - $96

I didn't get an industrial dissolved oxygen sensor for now (way expensive).

I was going to control all 110V devices directly, but I have the control box plugged into a GFCI outlet, and what I discovered was that fluorescent grow lights consistently trip off GFCI. So I added a non-GFCI powered Furman MP-15 to control the grow lights.

Once I get the box fully wired up, and operating/monitoring everything, I'll move on to graphical screens and long-term archiving.

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Replies to This Discussion

Permalink Reply by Vlad Jovanovic on February 10, 2012 at 4:04pm

Very cool Claude!

Permalink Reply by Rik Kretzinger on February 10, 2012 at 4:28pm

neat stuff -- looks like you are have some fun.....

Permalink Reply by Eoin Ross on February 10, 2012 at 6:10pm

I have one of those as well sitting ready for a project.
Throw an ECOM-100 module in that puppy nd you could have the PLC send emails even if the PC goes down :D

Permalink Reply by Panagiotis Kapsis on February 14, 2012 at 2:16pm

Very good work.. just give you some more ideas. I have work with F0-CP128 Triple Port ASCII CoProcessor module! You can do fantastic thinks with this module. You can interface with a MAX232 pH stamps, EC stamps and DO stamps from http://atlas-scientific.com/. With these stamps you can make a more sophisticated system for example to measure the dissolved oxygen In your fish tank and control the air pumps more efficiently. With this card also you can interface to the PLC a serial controlled LCD screens to display data. DL06 support a small LCD with 2 lines but you can build your own LCD with 4 lines. You can also use 2 digital inputs to make up and down scroll menus to the LCD. This is very low cost solution!

Permalink Reply by claude saunders on February 14, 2012 at 2:49pm

Ah! Clever idea. It does seem the RS232 interfaced sensors come out cheaper in general, so bringing the data in through serial is another solution. I've been all focused on trying to get the 0-10V or 4-20mA signal directly into the PLC.

One comment: the atlas-scientific site freezes up whenever I click on anything beyond the home page, so I can't get much out of it at the moment.

Permalink Reply by claude saunders on March 18, 2012 at 11:32am

A followup. I've pretty much got everything I intended to up and running. The control box now runs the light schedule as well as a twice daily feeding schedule. A feeding cycle involves turning off the pump, waiting 3 minutes for the backflushing to end, triggering the feeder, and then waiting 6 minutes before turning the pump back on. I got the EPICS control system software running and talking modbus to the PLC, and then created a control screen and line plot. Some photos attached here. I've started working with a nearby passive solar greenhouse project and hope to have another of these boxes up and running on a larger scale system.