Micrologix 1200 Relay Outputs - Normally Open or Closed?

[mike64b]

Maybe I'm getting confused because of all the topics on XIO/XIC or NO/NC instructions but I'm just looking at my PLC relay outputs on my micrologix 1200 and wondering if the relays them selves are normally open to current flow or normally closed (when power to the device is off)...

I'm assuming they are normally open, so that brings a question, is the only way to make them act like normally closed relays to install an intermediate relay?

I suppose the other option is to keep power on to the PLC at all times as normal and have the code initially set the relay to close.

 

[OZEE]

XIO/XIC actually refer to INputs, not OUTputs. Those abbreviations stand for "eXamine If Open" and "eXamine If Closed"

The related instruction for an output is OTE -- "OuTput Enable". They function as a NO relay contact.

 

[Wormfood]

Get a meter, set it to Ohms, and check out the contacts with it off.

Fluke Meters will show
OL for no continutiy for normally open.
Show 0.00X or beep (if set up) for normally closed.

As for the rest, your process needs should dictate if you can handle normally open contacts until the PLC closes them in your code (such as a power outage, or redownload of code).

 

[Mickey]

XIC/XIO Explained see link

http://www.patchn.com/index.php?opt...d=58:xioxic-explained&catid=20:plc&Itemid=118

And more good stuff

http://www.patchn.com/index.php?option=com_content&view=category&id=20&Itemid=118

http://ronbeaufort.com/sample_lessons.htm

 

[mike64b]

Hey guys thanks for all the help but I think there was some confusion on what I meant. I didn't mean to imply I don't get the XIC/XIO stuff I just meant that searching the forums for normally open relays ONLY brings up stuff related to that...

The true question I was wondering is if the contact OUTPUTS on the micrologix are normally open when the micrologix 1200 is powered off. However I went ahead and tested like a dMM like recommeneded and found they are indeed normally open.

Thanks!

 

[val_99]

You are really confused, I can see ;-). All PLC output modules have normally open outputs. The XIC and XIO commands you are referring too, are actually part of PLC ladder logic language and used to test or better to say inquire the state of inputs/outputs/memory bits etc. of PLC objects. It does not do anything with actual discrete output module other then may be used in a logic programming for it.

 

[mike64b]

yep thats what I was thinking, it just made it very difficult to search for "normally open relay" since it brings up a ton of questions regarding XIO/XIC instructions and not the physical relay operation itself heh

 

[OkiePC]

You are really confused, I can see ;-). All PLC output modules have normally open outputs.

I think he is just new, not confused. I have seen two PLCs with a form c contact (watchdog modules), and NC contacts are frequently available in other programmable devies like drives, so it's a fair question.

mike64b: Go through Ron B. sample lessons, and I guarantee you will learn a lot of useful information applicable to Allen Bradley SLC and PLC-5 programming. The Micrologix1200 is just a small variation on the SLC operating system and hardware.

 

[milldrone]

All PLC output modules have normally open outputs.

Not a totally true statement. The pic below is for a AD CLICK.

 

[mike64b]

I understand your argument daba but I think it's VERY application specific whether or not it would be catastrophic. In the wrong hands it could be but, assuming it is designed correctly it should be fine.

 

[val_99]

Guys, give Mike a brake. He was asking about Allen-Bradley Micrologix output module, confusing it with a PLC logic instructions.
Here is one of my favorite quotes: " It is quite simple to over complicate the things, it is more complicated to keep the things simple".