Ladder Logic Pull Command
- Thread starter asoliman
- Start date
bernie_carlton
Lifetime Supporting Member + Moderator
Please specify the specific PLC CPU.
It is not a function in a CPU PLC. It is only a ladder logic called Pull Command. I had this question in an exam and I didn't know the correct answer. The question was to identify the pull command from four given diagrams. As far as I remember, 1st diagram is two N.O. contacts in series with a latch. 2nd diagram is two N.C. contacts in series with a latch. 3rd diagram is two N.O. contacts in parallel with a latch. 4th diagram is two N.O. contacts in parallel with a latch. I think it is for a safety switch, if I'm not mistaken.
Thanks!
Thanks!
NetNathan
Lifetime Supporting Member
The only time I have ever run into "Pull" and "Push" commands in ladder was in talking to remote storage locations. "Pull" and "Push" were logic commands to read or write to logic locations in connected devices.
It was a York 620 PLC sold by Honeywell as part of SDC 9000 system.
It was a York 620 PLC sold by Honeywell as part of SDC 9000 system.
Peter Nachtwey
Member
Usually the term is push and pop and they are used for stack operations. Usually the stack operations are hidden from the PLC programmer. Where did pull come from?
Teachers testing on stupid terms that are not commonly used. They earn my contempt for torturing students with useless information.
Do a search for "PLC Pull command" to see how relevant know what a PLC pull command is when it doesn't show up on the first page.
College students today are being cheated.
Teachers testing on stupid terms that are not commonly used. They earn my contempt for torturing students with useless information.
Do a search for "PLC Pull command" to see how relevant know what a PLC pull command is when it doesn't show up on the first page.
College students today are being cheated.
very useful for 0.01% of programmers.
labeledas
Member
I thought the same thing Peter, was thinking more along the lines of other programming language array manipulation, still an odd question
jdbrandt
Lifetime Supporting Member
+1
I've seen equally silly questions, years ago, on employment exams, as if the answers to 15-25 year old technology trivia questions measure your employability.
Really, has anybody used BiQuinary in the last 30 years?
AustralIan
Member
My spidy senses tell me the question was asking more about "what is the most apporopriate function to use for a safety pull cord?"
The answer would be:
The pull cord will have two contacts that, when the cord is pulled both open.
If either of the contacts open, we need to activate (Latch) our safety logic.
For this reason, we need two parallel XIO and an OTL.
Note that this does not contain any logic to defend against short circuits.
The answer would be:
The pull cord will have two contacts that, when the cord is pulled both open.
If either of the contacts open, we need to activate (Latch) our safety logic.
For this reason, we need two parallel XIO and an OTL.
Note that this does not contain any logic to defend against short circuits.
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