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Unread September 15th, 2019, 02:29 AM   #1
franchois13
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PLC ladder Interrogation

Hi Everyone, I need some guidance on reading/working on ladder diagram.
Was trying to read a program in TIA 15 but there is a network below which I could not find where the coil is or what actually activating the contacts. I tried to searh the whole program but did not come up with anything.

---||------------------------(Q4.0)---

The contact is M100.3 but I checked all cross referenced networks and run a search but could not locate what activates M100.3.

Is there a way that this is hidden or maybe programmed in a different way?
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Unread September 15th, 2019, 02:53 AM   #2
Lare
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M-merker use same memory area than MW, and MD.
Check if MW100 is used somewhere on the program.


It is also possible that M100.3 is indectly addressed or even setted from HMI or scada directly.
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Unread September 15th, 2019, 03:01 AM   #3
franchois13
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Quote:
Originally Posted by Lare View Post
M-merker use same memory area than MW, and MD.
Check if MW100 is used somewhere on the program.


It is also possible that M100.3 is indectly addressed or even setted from HMI or scada directly.
Machine is not controlled by HMI/scada so I will take that option out. Will double check again MW and MD as you mentioned.
How can I find out if it is inderectly addressed?
Thanks.
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Unread September 15th, 2019, 05:41 AM   #4
cardosocea
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I don't think you can find if it is indirectly addressed really. :/



What does Q4.0 actually do? What is connected to it?



Thinking about it, there is another possibility which would be that the clock bit was configured in Byte 100 and Q4.0 is pulsing (either as a heartbeat or something else). Where is this rung located? and does the rung always process or does it have a jump to skip it or the function it is in?

I doubt it's this situation, but could happen.
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Unread September 15th, 2019, 05:55 AM   #5
franchois13
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Quote:
Originally Posted by cardosocea View Post
I don't think you can find if it is indirectly addressed really. :/



What does Q4.0 actually do? What is connected to it?



Thinking about it, there is another possibility which would be that the clock bit was configured in Byte 100 and Q4.0 is pulsing (either as a heartbeat or something else). Where is this rung located? and does the rung always process or does it have a jump to skip it or the function it is in?

I doubt it's this situation, but could happen.
Q4.0 is driving a run relay for inverter which is driving a machine infeed conveyor so it is actually operating quite frequent as the machine starts and stops. The rung is located in one of the FCs.

Last edited by franchois13; September 15th, 2019 at 06:06 AM.
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Unread September 15th, 2019, 10:35 PM   #6
Mike Lamond
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Quote:
Originally Posted by Lare View Post
M-merker use same memory area than MW, and MD.
Check if MW100 is used somewhere on the program.


It is also possible that M100.3 is indectly addressed or even setted from HMI or scada directly.
I have worked on other vendors' programs where one word was used to control a reversing starter, with bit 0 driving the forward output and bit 1 driving the reversing output. The program wrote 0 to the word at the beginning of the program, then several sections wrote 1 for forward or 2 for reverse when the logic was true. The cycle logic permitted only one section at a time to control the motor.

My preference would be to have a rung for each coil with branches for the output logic from each section. I consider this much better practice and far easier to troubleshoot.

Mike
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Unread September 16th, 2019, 02:16 AM   #7
cardosocea
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Do you see any logic anywhere written in STL? Usually pointers are easier or only possible to assemble in STL. So that would be an indication.

Is there a network connection to another PLC, perhaps? That would explain why you don't see M100 being written.

Can't think of much more without seeing the program. :/
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