Had Any Input Failures?

VOTE FOR AS MANY AS YOU LIKE!

I got to thinking today, I have never ran across any PLC input failures. So, I was wondering if it wasd the way I do things, or somewhat industry common. I acknowledge that there isn't a lot to do to smoke an input.

Obviouly, output failures are common, with overloading, etc.



regards.....casey

Casey

I have had inputs fail on me.

I had a Siemens S7 216-2 with 4 EM221's on one of our cranes that load containers onto railway wagons, I got called to attend because one of our technicians could not find the problem. The input module in question was indicating that the inputs were on, the respective LED's were lit up and everything looked OK. I plugged my laptop in, had a look at the program online, none of the inputs on one module were being read by the PLC. This module was not at the end of the line either, it was a 'middle' one. A power down then back up of the PLC cleared this fault, but 5 minutes later the problem was back. So a module change was carried out, haven't heard from it since.

Paul

kc9ih, your list is incomplete - there's no selection for unitary PLC's!

Have had a few input digital failures mainly due tome idiot connecting 240VAC to a 24VDC input. Cannot blame the PLC for that.

Have also had one analogue input failure due the failure of a transducer. Belted 240VAC up the 4-20ma input.

Have never had an output failure. I rarely use relay outputs and mainly use transistors with external relays fitted with flywheel diodes.

15 years experience here. Have had more trouble with power supplies surprisingly enough. Particularly Hitachi and AB.

Unitary and Brick should be similar enough.

regards.....casey

I remember hearing a discussion many years ago between two people about what would happen if you indavertantly put 110VAC on to a 24VDC input card (no, I wasn't one of them!!)

One was experienced in PLCs, the other was a novice.

Novice : (innocent curiosity) "So, is there any indication if you've wired in the wrong voltage?"

Master : (deadpan) "Yeah, sure. Most of the manufacturers have built-in indicators for this now. The smoke-emitting diodes come on."

Regards

Ken.

We have them fail actually. Our problem is moisture problems though. When your sanatation crew hoses everything down, and I mean everything, you will have those problems.

Somewhere on here I have a story about a dairy plant that had a case packer problem. ALL 3 shifts replaced every part they could, mostly pneumatic valves. I had just started to work there and was asked to look at the AB SLC fixed I/O plc. I determined that an input (I think it was an input) was bad even though the led was lit. They had spare I/O but I didnt have a PC, software or handheld to make the changes. They did have a spare unit though and it had a memory module so in 30 minutes could have been changed over. The supervisor decided to replace parts again, they spent another 4-5 hrs changing parts.

About 5:30 AM just prior to day shift startup they asked me to make the swap with the spare, it was running before 6.

I have seen alot of both fail, usually due to external problems..ie shorts etc.

Please don't remind me about heavy washdown. We had all the 24 volt cards in one PLC burn out because they wired 120 volt next to 24 volt terminal strips with no seperation. Water bridged the gap and poof one huge smoke show. About 30,000$ of equipment gone

I've seen inputs go bad:

1) When 480vac 1-phase is landed on 24 vdc input modules (makes everything go boom)

2) When electricians punch 30+ holes in the tops of 3 enclosures(that were pre-drilled for bottom-entry) and don't cover the components in the cabinets. Metal-shavings and cutting-oil are very good conductors, it turns out. But that was a $50,000.00 lesson the contractor just had to learn.

Yea, usually...no always due to poor system design, or wiring errors.

How about a whole system meltdown!!

Had one system made up ready to go but had the chance to move to another plant for the same company, when I left I told the other tech to make sure he hooks up the nitrogen purge to the enclosure(it was going to be in a acid fume area). Well they shutdown that process in about six months. Didn't think anything about it until I got a call from the other plant to come down and disconnect the PLC so it could be used in another application.

When I got there they had it out of the enclosure, looked at me and asked if I can fix this. Well I looked at it and it looked like someone took a torch to it. Plactic melted, back plane ate up and cards falling out. The other tech never hooked up the purge.

They didn't like my answer when I just turned around to leave and told them to throw it away.

That's the only failures I've had.

In 20 years, I've yet to see an input module fail. :knock_on_wood:

Of all the times I did PLC setting up(countable with 2 hands), I have so far only came across a small situation where the voltages have been reversed. Maybe when I did something really dramatic that will caused the whole device to explode, I'll you guys know.

Regards
Sherine T.

Most of the ones I`ve seen fail were caused by by whom ever designed the plc in the first place. Because when you come straight off of the coil on say a NEMA size 5 or 6 starter and go to your auxillary contact and then back to your input, for some unknown reason inputs dont like this and like one of the previous post said, the lights on but no one was home. The light would come on, but it must have fried one of the little dog ticks inside. Once you realize that whom ever designed the plc has made this design error, it is easy enough to correct by not coming off of the big fat coil with your input. Of coarse this means you have to run another hot wire all the way over there just to get your input. The next flaw in their design is that they won`t switch some hydrolic coils but a couple of thousand times and they`re fried. Who designs these things anyway??? By the way it had to be the designers fault as HE was the only one that wasn`t there!
bonkhead :site: