PLC Rookie

DonnyMontobaun · Dec 8, 2009

Basic question, I'm having a hard time with terminology,

"devise a circuit that will turn on a light to indicate that a momentary input signal existed at one time, but is no longer present. An acknowledgement, a momentary pushbutton will turn the light off"

I need helping seeing this as a ladder diagram.

Thank for any help.

D

Mickey · Dec 8, 2009

Hint...
"Latch"
So your work and forum members will help.

Bruce99 · Dec 8, 2009

set reset

Mickey said:
Hint...
"Latch"
So your work and forum members will help.

Yes use the ol' latch and reset to do this.
Mickey is right. look it up in the manual and play with it...

Mickey · Dec 8, 2009

Mickey said:
Hint...
"Latch"
Show ( not so) your work and forum members will help.

I meant show your work. Too much sun.

ydtech · Dec 8, 2009

Could use a seal too.

shoelesscraig · Dec 8, 2009

Sounds like another homework assignment to me...

OZEE · Dec 9, 2009

Yeah, it's probably in your textbook if you'd bother to open it.

PhilipD · Dec 9, 2009

OZEE said:
Yeah, it's probably in your textbook if you'd bother to open it.

That was uncalled for. The OP might like be like me -- learning independently without benefit of textbooks, instructors or a structured course. He is asking for help, not SA comments. Give him a break.

rdrast · Dec 9, 2009

PhilipD said:
That was uncalled for. The OP might like be like me -- learning independently without benefit of textbooks, instructors or a structured course. He is asking for help, not SA comments. Give him a break.

Then download ANY manufacturers programming manual. Every single one of them has a programming manual available, all of which show common circuits like this.

No textbooks? No instructors? No resources? Then you can't learn it. Poking around is not the way to go.

Effort first. Once effort is shown, then answers become more meaningful.

shoelesscraig · Dec 9, 2009

The original poster obviously has the internet, otherwise he wouldn't be on here. So it isn't too much to expect him to research first before he posts such a elementary question...There must be about a million places you can find an example of what he is looking for.

tomalbright · Dec 9, 2009

shoelesscraig said:
The original poster obviously has the internet, otherwise he wouldn't be on here. So it isn't too much to expect him to research first before he posts such a elementary question...There must be about a million places you can find an example of what he is looking for.

Well, hmmm.

seaston_65 · Dec 9, 2009

Yeah...pretty much, that's how I found this site.

Stationmaster · Dec 9, 2009

Two observations guys:

1) He DID do some research, he looked US up, found US, and posted his question HERE. Aren't WE a resource?

2) If you read the question he poses CAREFULLY, a simple LATCH (or SEAL) circuit doesn't quite fill the bill. The simple phrase "but is no longer present" presents a condition that a simple LATCH circuit doesn't fill. In a simple latch circuit, the light will be on whether the momentary signal is still there or not.......

There will have to be a NC contact of the momentary pushbutton added on the output of the latch... before the lamp. Perhaps that is the visualization with which he is having trouble.

Now I'm probably the biggest SA in the in the mix, but given the two observations above, maybe a SA answer really ISN'T warranted.

Just my 2 cents :8)

Stationmaster

Clay B. · Dec 9, 2009

Something to google that may shed some light on this is "motor starter circuit".

A motor starter circuit is a good real world example where a momentary switch is sealed in and how the stop button releases the sealed circuit. The difference here is you firing a light where a motor starter circuit runs a motor.

ydtech · Dec 9, 2009

The 'no longer present' part got me too. But it's just another bit of logic to add to the latch or seal-in part. PLC tutorials are to be found by the bucket-load over the net. All of my problems I've solved by 1) RTFM, 2) scour the net and 3) post it up. Very rarely have I needed 3), since most of the time somebody else has already had the same issue and I can read the tips he got.

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