I need to control solenoid valves in an irrigation system over an existing two wire network. There is an existing irrigation control that does this now, but is very limited when it comes to any sort of complicated control functions, like moisture inputs, etc. The client wants to replace all of it with a new system that will tie into an existing iFix HMI.

What protocols or options are there for doing this? There are some runs that have up to 90 valves daisy chained together...almost 800 valves split up over several networks (13 I think?). From what I can gather, the existing controller sends out a "pulse" to both tell the correct valve to open, plus actually swap the valve state.

Thanks for any help or insight.

 

You could consider running a straight RS485 Modbus RTU protocol. At
speeds under 115Kbps, you can run up to 4000 feet and have up to 31
devices before needing an RS485 repeater to go another 4000 feet and
drive additional devices.


Modbus RTU does not carry power over the two wire network so you'll need power at the remote locations. But, it is a simple, open, and reliable method to remotely control the valves.

Acromag offers very good RS485 Modbus RTU DIO modules for the remote i/o consideration. Below are some links to some modules and a whitepaper. Each module is "multi-channel" but only represents 1 device on the network. You can "daisy-chain" RS485 modules to get the right amount of i/o you need in each zone. Also, I think you'll find iFix supports Modbus RTU protocol as well.

Model 903MB-0900, 12ch DIO w/ low side switched outputs
http://www.acromag.com/parts.cfm?Model_ID=80&Product_Function_ID=27&Cate
gory_ID=13&Group_ID=2

Model 906MB-0900, 12ch DIO w/ high side switched outputs

http://www.acromag.com/parts.cfm?Model_ID=83&Product_Function_ID=27&Cate
gory_ID=13&Group_ID=2

Whitepaper on Modbus RTU: White Paper: Introduction to Modbus
<http://www.acromag.com/authentication.cfm?thepage=manuals/900MB_whitepa
pers.cfm&group_id=2> , PDF 83 KB

Kind Regards,
Donald Lupo ([email protected])

 

AS-i (Actuator Sensor Interface, roughly sounds like Ozzy Osbourne's first name) is the only one I know of. Of course, it's 24VDC, so if the solenoids are 110VAC (or some other weirder thing) you're out of luck. Plus, if you wanted to put the valves directly on the bus you'd have to replace all the existing valves. To keep the valves you'd put little I/O blocks around.

AS-i can only handle 62 nodes on one network, but with multiple outputs per node you could conceivably get all 90 valves. AS-i can handle analog devices, but one device will take up multiple nodes.

AS-i requires a controller and a power supply. You'll need one each for each network. They aren't exactly cheap, either. The controller will talk any way you like (serial, Ethernet, various industrial networks) or even be programmable.

Good luck.

-James Ingraham
Sage Automation, Inc.

 

iFix has loads of drivers for communications. This is probably the smallest piece of the puzzle. As was mentioned, RS-485 is not a bad choice from a hardware stand point. It is probably more forgiving than other systems depending on the cabling that is already there. Many modern communications systems are designed for higher speeds and want minimum wiring requirements. But if this apllication is out doors, you may want to look at wireless modems depending on the ranges involved.


Regards,
James Fountas

 

This is something already done by cheap, commercial irrigation companies. See this:

http://www.rainbird.com/landscape/products/controllers/MDC2.htm

I don't have the option of anything requiring separate power, no power out at the valves. If Rain Bird can do it, I think I can find a solution to do it from a PLC, etc.

 

Well, that's pretty cool. And it has a serial port. Why not just tie the PLC to the RainBird through the serial port?

-James Ingraham
Sage Automation, Inc.