Most Common PLC Use?

I got a call this evening from a young and energetic technician/inventor. He posed several questions, that I couldn't readily answer.

1). What is the most common use for a PLC? Not traffic lights or washing machines. Machinery and automation equipment were to vague an answer.

2). What has not had a PLC been used for yet? Good question. I've even used them for doorbell circuits.

3). What is the biggest failure problem on PLC's? My guess was outputs that were smoked. Power supplies would be my second guess. I think I did a poll on this one.

So, what's your thoughts guys?

We have a budding genius out there, wanting to unload his potential.

regards.....casey

I would hazard a guess that the most common PLC application are small water pumping stations. Most of them have a pretty low IO count but there must be 100's of thousands of them out there in the world.

I'd say that the most common use of PLC's is to replace relays.
(how's that for ducking the question?)

ok

I agree with gbradley and PhilipW they replace alot of relays and used in small water pumping stations. It would surprise me if there is a manufacturing plant out there that doesn`t have some plc control in it if not all plc controlled. Most of the input and output I`ve seen fail I caused. Have replaced a couple of racks not my fault. There was a problem with some 05s, but it was actually a mechanical problem where the terminals attached to the plc. Seen some that that cards just needed unplugged and plugged back in dust I guess. They just seem to work and keep on working. Everything here municipal and industrial= papermills, sawmills, Stran board, particle board down to the lift stations are plc controlled. The biggest failure problem I see is in management they think everyone that has a tool pouch is an electricain and anybody that can turn on a computer is a programmmmer bonkhead

:site:

the most common use of PLC's is to replace relays.

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Absolutely agree.

What is the biggest failure problem on PLC's? My guess was outputs that were smoked. Power supplies would be my second guess. I think I did a poll on this one.

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Power supplies.

anybody that can turn on a computer is a programmmmer

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Sounds like IT people. PASS!!!!!

What has not had a PLC been used for yet? Good question.

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Cannot think of anything.

My Question is why do they put a $200 PLC in when they can use 3 $5 relays? And their is the one they put a little PLC in and add 50 Relays.

I realy like this one, they have 10 switches to turn on 10 inputs to turn on 10 outputs that go to 10 relays. Daaaaaa

That is my question, Why do people miss use PLC.

They can teach engineres how to drive the train but won't give them the keys

Rich1955

A small PLC can be cost efficent for replacing a few relays and timers because you dont have to wire the circuit, and can easly change the program, or add to it at a later date. Anything that requires a logic circuit of 4 or more relays and a timer or two is a good canidate for a small $100.00 PLC like the AD DL05.

That is my question, Why do people miss use PLC.

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How do you misuse a PLC? They were designed to replace relays and minimize wiring.

I use them all the time to replace relays, especially timer relays....KEYWORD: Expandable...ie allows for more options if (actually thats when) needed in the future.

AND the outputs may turn on relays, the relays may be needed for isolation and power requirements it just depends.

Once you have started using plcs, have the software, cables etc the cost of a plc vs relays isnt really an issue, especially if there are timers in the circuit.

At the cement plant I used a cheap "brick" to replace a specialty "timing" board
PLC cost $150
Board cost to repair $350 to 400, couldnt buy new.

I have used the DL05 (and other brands) in just about any application where I need A timer..$100 for DL05 $100 for a programmable timer. Why not?

Rebuilt some sealers that were hardwired using power relays. The power relays would stick and cause the cut wire to burn out. I had some used GE plcs, the software and adapter. I rebuilt the sealers using the used plcs and used relays. Once done the wire could be "pulsed" to maintain heat, used solid state relay for cut wire...no more sticking. The machine(s) went from burning cut wires 4 to 8 times a day to none in several months.

I guess its a matter of opinion.

I am not sure that the question "Where hasnt a PLC been used" is the right question. What would be more appropriate is "Where CANT a plc be used?"

(Quote
anybody that can turn on a computer is a programmmmer


Sounds like IT people. PASS!!!!!

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... setup plc to send tease emails to IT guys and play hide and seek.
how long till they figure out it was not sent from any of the PCs?

"What has not had a PLC been used for yet? Good question."

I always think why people do use PLC to control the Christmas lights at home?

think about the pattern you can make?

gene

Misuse PLC

Let me give you some examples.
I open up a panel the other day and saw a AD 06 looking at me.This panel is less than 2 years old and you know what it does. It moves a spray head back and forth on an air cylinder. This all it does, talk about overkill.

I open up another panel less than 3 years old and saw 30 relays, 6 timers 2 temp controls, there were 20 panel lights and 15 switches and no PLC or touch screen. They wonder why they are having problems.

Sorry just venting

Let PLC do what there are desinded to do, leave some room for addons.
Use them the right way and they will last, making our jobs easer.

I found a better example

This is an AD 6 slot, 240 CPU

Rich,

I think your exapmles are more of a question of what PLC rather then PLC or not.

I couldnt have said it better then Ron, so I'll leave it at that..

Rebuilt some sealers that were hardwired using power relays. The power relays would stick and cause the cut wire to burn out. I had some used GE plcs, the software and adapter. I rebuilt the sealers using the used plcs and used relays. Once done the wire could be "pulsed" to maintain heat, used solid state relay for cut wire...no more sticking. The machine(s) went from burning cut wires 4 to 8 times a day to none in several months.

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This machine needed less than 20 I/O total. The GE 90/30 was a 5 slot rack type unit. That was overkil...but they were used/free.

I can not state why someone would use a rack system when a "brick" could be used. It could have something to do with maintaining uniformity in all equipment..ie they build many systems but just use ONE (1) model PLC.

As the cost of PLCs lower I dont see a reason not to use them if/when you can.

What is the most common use for a PLC?

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I'd venture a guess at packaging machinery, because packaging seems to be the most common element amongst all retail goods.

Except for produce and eggs, what do you buy in a grocery store that doesn't have some PLC association?

Dan