What is your definition of logic in PLC programming?

When somebody says "The logic of the pump is right," what exactly are they referring to? The ladder logic code or the controls of the pump?

You should ask the person who says it!

Generally I'd interpret this as the ladder logic being correct, unless there was no PLC. You can of course implement the same "logic" in a physical form using discrete relays.

david90 said:

When somebody says "The logic of the pump is right," what exactly are they referring to? The ladder logic code or the controls of the pump?

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The PLC code. It may not be ladder, it could be any one of the PLC languages.

https://www.google.com/search?q=IEC...122&ie=UTF-8#q=iec+1131+programming+standards

One possible explanation:

The pump has been working fine for months. Suddenly it no longer works properly. The pipefitter says, "There must be something wrong with the program". The programmer defends his turf by saying, "The logic is right. The problem is mechanical".

What word do you guys use to describe the operation or behavior of a component? For me I use "controls." I'm just trying to get a feel of how words are used. I have encountered a lot of confusions due people not agreeing on the definition of PLC words.

"functional specification/description"

The reason for the inevitable troubleshooting question, "has it ever worked or is this a new installation/commissioning" is to determine whether there is or has been functional control logic.

I frequently hear 'it's the program', without the finer distinction that a program is logic.

And most operators will point at the HMI display when they're blaming the logic/program/controls, because the HMI is the messenger and the messenger gets blamed for the fault.

danw said:

The reason for the inevitable troubleshooting question, "has it ever worked or is this a new installation/commissioning" is to determine whether there is or has been functional control logic.

I frequently hear 'it's the program', without the finer distinction that a program is logic.

And most operators will point at the HMI display when they're blaming the logic/program/controls, because the HMI is the messenger and the messenger gets blamed for the fault.

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sometimes it is the program. but way more often it is a physical device in the process, but if order to.determine that, you need o see what is happening in the program... and then after you fix it they think it was in the program still. lol

DwSoFt said:

sometimes it is the program. but way more often it is a physical device in the process, but if order to.determine that, you need o see what is happening in the program... and then after you fix it they think it was in the program still. lol

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Absolutely!!
The programmer has to diagnose the problem and usually replaces the bad component or re-connects the loose wire then the program gets blamed as the problem.

david90 said:

When somebody says "The logic of the pump is right," what exactly are they referring to? The ladder logic code or the controls of the pump?

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IMHO, it would mean that the "truth" table controlling the pump is correct.

I see a problem with this as too many are taught that "Truth" is what "I" say it is today. The truth is that there actually is a "Truth" that can't be changed.
This not only in physics but in life too.

Originally posted by david90:

"The logic of the pump is right,"

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There is not enough context to that statement is to figure out what the speaker intended. As RussB stated it could be that the speaker intended to say that the planned operational sequence is correct for the application but it could just as easily mean that the program or physical implementation of the sequencer is theoretically and/or functionally correct.

There are some words in the english language that cannot be used in a vacuum. "Logic" is one of those words. As for "controls", I think in terms of systems and packages when that word is used. That one has an even broader meaning than "logic".

In these cases make sure you have the speaker define exactly what they mean when they say stuff like this unless the conversation contains enough context to allow you to infer the meaning. For example, if you spent the last 5 minutes talking about the plc program and the speaker comes out with "The logic of the pump is right," you can very likely assume he is referring to the plc program. If you spent the last 5 minutes talking about the timing sequence of the pump motor and valving and he says "The logic of the pump is right," you can probably assume he is referring to the timing and sequence design of the system. In the end, if you aren't sure, ask.

Keith

To me this just sounds like a very basic expression that everything seems to work like it should. The end-user/operator is happy