RS-232 with 24V signals...

Before I bother trying it, I'd like to hear opinions on this...

I need to make a hardwired operator panel disconnect-able. It's just a simple text display (Automation Direct EZ-420) and 3 pushbuttons (24VDC inputs to the PLC). The question is can I run the RS-232 signals AND 24V signals in the SAME cable without causing problems?

I was going to run a piece of liquidtite with a separate shielded cable for the RS-232, but was hoping I might be able to get away with regular multi-conductor cable (i.e. Olflex 190). Total cable length will be about 2m, with the connection through a Harting type connector.

If this is a stupid idea, then how about using multipair individually shielded twisted-pair cable?...

Or, have I simply lost my mind?...

beerchug

-Eric

With a clean 24 VDC power supply, I don't think it should be a problem.
Using a multi-pair individually-shielded cable would make you feel safer than sorrier...

I would have absolutely no qualms with doing this at all.The ones you really wanna stay away from are the ac signals particularly higher voltage ones and seeing how it is such a short run I reckon not a problem at all.
Tom

I dont see an issue with this. 24vdc doesnt induce like AC would and naturally the low strength RS232 signal wont affect the 24vdc. I have worked with systems that have done this in a variety of ways each using a single flexible cable. Some of the more elaborate were actually multiple multi-wire cables inside a shielded cable housing, these may have been special order. I have also seen and used a clear (sometimes amber) plastic conduit (looks like transparent rubber hose) and put both single wires and shielded cable inside of it, a make your own cable type thing. I cant find a link to it now but I will look it up when I get to work tomorrow.

By the responses so far, I think I'll give it a shot...

Additionally, these pushbuttons will be used very infrequently, and the RS-232 is running at a slow baud rate (9600bps).

Well, that's slow by today's standards. I can remember upgrading a 300 baud modem to a 'screaming' (and expensive at the time) 1200 baud version...

Thanks for the feedback!... :site:

beerchug

-Eric

If you want to feel better use NPN inputs you will switch same ground like you switching in RS232 and you will need one conductor less.

You can increase your chances of success if you somehow change the RS232 to RS422 (or RS485). Maybe the EZ panel has a version with RS422/RS485, alternatively you can use converters.

From what you describe, I would come as close to guaranteeing that it would work as I would in any situation. 9600 baud to an error tolerant touchscreen? Cake.

Just don't set it on the welder.

By the way, does anybody uses the metal ferrite they send with them HMI from A-Direct?

I sure don't but am I the only one?

Has anybody encountered problems, when not using them, which where solved when they install those pieces?

The ferrite cores are required for one of the Canadian Standards groups (CUL, CSA) if I remember correctly. Supposed to cut down on any EMI on the power and communications wires.

Eric, I don't see why it wouldn't work. I have done it in the past with no problems, although RS-422 would be a better choice, IMHO. Lot better noise suppression with RS-422.