Logix Pro Compressor Exercise #3

chrisk_81 · Apr 9, 2011

Would love some feedback from anyone with PLC experience on how this solution looks. It satisfies all the criteria for exercise 3.

Cheers

diat150 · Apr 9, 2011

I dont know what the exercise consists of but why would you use the equal instruction instead of the timer dn bit?

chrisk_81 · Apr 9, 2011

Thanks for that! Much appreciated. I don't know why I didn't realise that before. I've updated my solution and added another rung just to make the program read a little clearer.

chrisk_81 · Apr 13, 2011

My solution to Compressor Exercise 4.

theDave2 · Apr 13, 2011

Never, ever, use outputs as contacts unless it's to interlock 2 devices that should not, cannot, be on at the same time. Never.

Why #1: If you force an output, then other logic is activated.

Why #2: If the output goes bad, you have multiple places in logic to change.

chrisk_81 · Apr 13, 2011

How should it be done? Use a bit location that's referenced by the output and contact?

diat150 · Apr 13, 2011

chrisk_81 said:
How should it be done? Use a bit location that's referenced by the output and contact?

usually what I do is I build a subroutine that couples just digital input connections, and digital output connections to the various bits that I use in the program. build your program using bit references and then just tie the bit reference to the input or output in the new subroutine.

so in your case you could name a free bit in your program comp run command. use that bit everywhere that you have the o:2/2 as an instruction.

then in your subroutine that handles the coupling you would tie the bit into the o:2/2

shoelesscraig · Apr 13, 2011

theDave2 said:
Never, ever, use outputs as contacts unless it's to interlock 2 devices that should not, cannot, be on at the same time. Never.

Why #1: If you force an output, then other logic is activated.

Why #2: If the output goes bad, you have multiple places in logic to change.

I have dozens and dozens of machines in my plant that were written this way from the factory. If done properly, there is absolutely NOTHING wrong with it. Saying "NEVER" to do it is an asinine statement. Let me guess, you are one of those guys that NEVER EVER uses a latch instruction either...? Because doing that is BAD as well I suppose...

Mickey · Apr 14, 2011

theDave2 said:
Never, ever, use outputs as contacts unless it's to interlock 2 devices that should not, cannot, be on at the same time. Never.

Why #1: If you force an output, then other logic is activated.

Why #2: If the output goes bad, you have multiple places in logic to change.

I will have to politely disagree with number one. See picture below.

muusic_man · Apr 14, 2011

theDave2 said:
Never, ever, use outputs as contacts unless it's to interlock 2 devices that should not, cannot, be on at the same time. Never.

Why #1: If you force an output, then other logic is activated.

Why #2: If the output goes bad, you have multiple places in logic to change.

I completely and whole-heartedly dissagree with your #1. As far as #2 it's a simple find and replace. No big deal.

chrisk_81 · Apr 15, 2011

Hmmm. Maybe I'll keep using my outputs as contacts.

Logix Pro Compressor Exercise #3

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