View Full Version : Modbus Serial Remote IO

April 5th, 2005, 07:09 AM
Greetings all,

I've been working with Unitronics using modbus and an M91 as remote IO and igt worked like a charm. That said, the only thing I'm dissatisfied with is the size of the panel. To support the M91, I needed relays, a valve stack, terminals, track, etc, and my "IO drop" wound up half the size of my main panel.

So now I'm hunting for some more size-effective remote IO that is RS485 serial modbus based. I'm envisioning something like the Numatics series 2005, integrated comms, inputs and outputs, all with a comm and power cable, that mounts right to the frame of the machine.

I've been doing some digging, and I've found alot of modbus remote IO (wago, a couple of others), but nothing direct machine mount that would not require an enclosure. All the stuff with the physical footprint I'm after (like the Numatics) is devicenet/fieldbus/profibus compatible, but no modbus.

Has anybody seen such a beast? And where?



April 5th, 2005, 08:14 AM
Did you goto www.modbus.org (http://www.modbus.org/) and check the device database?

May want to look at the Beckhoff stuff, especially the Fieldbus Box section. http://www.beckhoff.com/english.htm

April 5th, 2005, 08:46 AM
Thanks Ron!

I checked out the Modbus.org site so fast, I didn't finish reading your message - and you're right, the beckhoff stuff looks outstanding.

Interestingly, the Mac valves look right, and are listed as verified, but there is nothing at their site about modbus capability. Might need to call them.



April 5th, 2005, 08:50 AM
No Modbus (yet?) DeviceNet and Profi but it doesn't require a enclosure (its IP67).

April 5th, 2005, 09:40 AM
So'kay, here's what we got so far:

Mac offers the manifolds, although it's not widely known. Pricing depends completely on application, so no idea there.

Beckhoff is outstanding though. An 8-point input module IP1001-B730 will cost about $242 (sinking inputs). An 8-point output module is IP2001-B730, at $262.

Best for Beckhoff is their specialty modules. They have 100Khz high-speed counters, and even a 1Mhz encoder module. The Enc is just $378 (availability unknown).

Oooo boy, I'm excited... gotta get me summa these!

April 5th, 2005, 10:31 AM
here's another from Turck that is Modbus and IP67 Don't know availibility.


Stephen Luft
April 5th, 2005, 10:56 AM

If you are already using ModBus, why not just use another PLC and network them together?

For the cost of the 8 point input module and 8 point output module, you can get a PLC with RS485, and ModBus RTU, and still be less.

April 5th, 2005, 07:21 PM
Hi Stephen,

Specifically, I'm looking for an on-the-machine solution, as opposed to someting that needs to go inside an enclosure. I'm trying to avoid the bulk of added relays, terminals, and additional wiring of Local I/O to same.

The devices Ron pointed me to are machine-mount IP67 rated, and can just be cabled without any additional enclosure. Imagine - a Vision 280 PLC running the entire machine with an enclosure just big enough for the power supply (woo-hoo!) and all I/O distributed locally to stations around the machine.

The prices are higher, but not that much higher, an extra $1500 on my current project. But the savings in time, and sheer aesthetics, will be huge. Elegant automation!


April 5th, 2005, 08:09 PM

I'm looking for a Modbus RTU (RS-485 and or TCP) master, with enough brains to be able to convert integer to floating point and vice versa (read an integer, writes same as a float). A PLC controller with no I/O is fine.

Whatcha got? specifics . . .


April 6th, 2005, 06:45 AM

Sorry to butt in, but take a look at the Unitronics Vision 280. $600 with no I/O, 4.5" touchscreen for data entry/display, modbus RTU master serial AND ethernet based. Two serial ports, if you need RS-485, gotta buy a convertor for $99.

Specs at Unitonics.com. they also have some smaller (cheaper)models that might fit your needs. Check the Vision 120 capabilities.