micrologix ethernet messaging or wired I/O

I am putting in a system with a couple of plc's and a panelview plus.
Currently panel 1 has a micro 1100 with a panelview plus talking via ethernet. I am installing a second panel with a micro 1400 about 600 feet away.

The micro 1400 is controlling a few fans and conveyors, but i want them to be started and stopped based on logic in the original panel. I am sending a few analog values from the second to first panel via ethernet messaging.

My question is, would it be better to send the stop start commands from the first panel to second via ethernet, or should i use hard wired i/o (outputs from first panel, to inputs in second panel)

Let's think about what will happen if you miss messages? If you don't get a start signal in time what happens? Probably more important what happens if you miss a stop command?

http://www.plctalk.net/qanda/showthread.php?t=56882&highlight=repeating+msg


I sort of had the same question and found some useful information in the post above. It deals with setting up repeating msg instuctions and timeframes. The purpose of the repeating logic is so if a message gets missed, it should get it on the next go round.

Obviously, if human safety is involved, you should have hard wired interlocks on the machines involved. That can be done at the site 600 ft away.

Depending on the number of fans and conveyors involed, 600 ft of copper at todays prices can get pretty astronomical compared to 600 ft of Cat5.

Hope this helps,
Roy

The end decision is yours to make. You can set up logic for handshaking where if the message is lost the local controller stops the process. For pumps and fans this is routine. You must decide if it must be hard wired. We do it both ways. It's a judgement call.

I would use Ethernet.

This doesn't sound like an application where things will go to pieces in a fraction of a second. 600 ft is too far without a repeater or switch.

Peter Nachtwey said:

This doesn't sound like an application where things will go to pieces in a fraction of a second. 600 ft is too far without a repeater or switch.

Click to expand...

I'm using a fibre optic media convertor for ethernet run

If the problem is wiring signals 600' away, why not look at some wireless I/O. I've had very good luck with Banner's DX70s and DX80s
http://www.bannerengineering.com/en-US/wireless/surecross_web_prodselect

I think i will hardwire the output wiring, and use ethernet for status signals going back to the main plc (o/l trips etc)

About 4 days ago there was a thread on here discussing bouncing signals for a prox switch.

Someone there did the math for voltage drop, not to mention the RF gain from such a long run.

Something to look at I think.