Problem to understand mitsubishi PLC logic

mraj2001 · Jul 5, 2009

Hi,
I am newly joined member working as an electronic engineer in a process plant.
I have a problem in a m/c equipped with Mitsubishi PLC Fx-1N-40MR.
I have not done any plc programming course, but i know it by practical experience only.
I have Gx developer V8.0 PLC programmer and unable to understand in PLC program that memory NO/NC contact used to run a step are not defined as a coil in the program. Therefore I dont know when any of these memory signal will be true/false. In general suppose M100 is an out put comes ON when power ON flag is ON. M100 is a coil here and i can use it as NO or NC contact in other steps. But in my plc say M508,M503...... are used as NO contact only but not as a coil. These is the problem to understand when M508, M503 will be ON.

geniusintraining · Jul 5, 2009

Hello mraj2001 and welcome...

It would be easier if you attached the program so we could have a better understanding of what you are talking about.

Viks · Jul 5, 2009

Hi mraj, this is what i understand from what you have posted in your first post. You have certain NO/NC operands in parts of your program which from what you assume should be contacts of an output coil but you cant seem to find the OTE's with those addresses anywhere in your program,right! I do not have much experience with Mitsubishi PLC's but would like to help you out with whatever i can. First of all,is the equipment connected to the PLC currently operational? If so,what process is not taking place? Have you consulted with others who carry out maintenance on the equipment and work on the PLC if they have changed something? It could also be that these bits are inputs from the equipment itself(sensors,limit switches,etc.) If you could post a copy of the program here, someone will surely be able to help you out because we havent seen your equipment and have no idea how the process works.

Sergei Troizky · Jul 5, 2009

Here are some possibilities:
1. These bits receive result of group output instruction, such as bit shift register.
2. Group of bits receives result of instruction, being grouped into word (KiMn format).
3. These bits are set/reset from external device, most probably operator display.
4. Being latched bits, these may be debugging and/or diagnostic switches or mode selectors, not subject to change after machine startup.

mraj2001 · Jul 6, 2009

geniusintraining said:
Hello mraj2001 and welcome...

It would be easier if you attached the program so we could have a better understanding of what you are talking about.

Thanks to look in my problem. I tried to attach PLC program but failes to attach. Please give me your mail id to send the same.

parky · Jul 6, 2009

Also in mitsubishi compare instructions use three bits i.e. m500 m501 m502 for < = > if the cmp instruction is programmed like: CMP D1 D2 M500 then bits 500 to 502 could be on dependant on the data in D1 D2, there are other instructions that use bits that may not be cross referenced in the program or they could be indirectly addressed i.e. m500Z will refer to the offset of the index register Z if Z = 2 then M500Z would refer to M502 if Z was 500 M0Z would point to M500.

Topcat · Jul 6, 2009

I believe the question is more simplistic than than the answers. Aj are you saying that the NO and NC contacts have no written labels so you cant identify what the contact does ? Thus making the determination that the statement is true or false very difficult.
Also in the Melsac language "X" equals an actual input to the PLC and "Y" equals an actual output."M" of the M100 you speak of is am internal register that is used to carry a true or false answer to be used elseware in the progam.
I could be wrong just a different take on the question...

geniusintraining · Jul 6, 2009

mraj2001 said:
Thanks to look in my problem. I tried to attach PLC program but failes to attach. Please give me your mail id to send the same.

[email protected]

Look at the comments from others that posted... parky is much better then I am when it come to Mitsubishi..., but send it to me and I will post it here so you can have several looks

panic mode · Jul 7, 2009

mraj2001 said:
Hi,
But in my plc say M508,M503...... are used as NO contact only but not as a coil. These is the problem to understand when M508, M503 will be ON.

there could be several things to this, the best you can do is ZIP your program and post it here. examples of cases where you see bits but no coils could be:
- they come from HMI buttons
- they come from another PLC if networked
- they are copied from somewhere else(using MOV, BMOV, FROM for example)
- they are results of other word-level instructions (WAND, WOR, WXOR, DECO etc.)
- some of them (M8000+) are system flags

mraj2001 · Jul 7, 2009

geniusintraining said:
[email protected]

Look at the comments from others that posted... parky is much better then I am when it come to Mitsubishi..., but send it to me and I will post it here so you can have several looks

thanks sir to do help me, different posts will be helpfull for me. How I can get a programming manual for Mitsubishi PLC using Gx developer on free so that I can study and follow the suggestions.Because I have not done the programming course. Can you help me please.

mraj2001 · Jul 7, 2009

parky said:
Also in mitsubishi compare instructions use three bits i.e. m500 m501 m502 for < = > if the cmp instruction is programmed like: CMP D1 D2 M500 then bits 500 to 502 could be on dependant on the data in D1 D2, there are other instructions that use bits that may not be cross referenced in the program or they could be indirectly addressed i.e. m500Z will refer to the offset of the index register Z if Z = 2 then M500Z would refer to M502 if Z was 500 M0Z would point to M500.

Thanks sir to look my problem. I will try to understand the program but I have not done PLC programming course and to learn I need a programming manual for Mitsubishi PLC through that I will be able to understand very well. Can you help me please to get the manual.

mraj2001 · Jul 7, 2009

problem in PLC

panic mode said:
there could be several things to this, the best you can do is ZIP your program and post it here. examples of cases where you see bits but no coils could be:
- they come from HMI buttons
- they come from another PLC if networked
- they are copied from somewhere else(using MOV, BMOV, FROM for example)
- they are results of other word-level instructions (WAND, WOR, WXOR, DECO etc.)
- some of them (M8000+) are system flags

please look the zip file.

mraj2001 · Jul 7, 2009

What is the meaning of
[DMOV K0 K6M501]

in Mitsubishi PLC program.

panic mode · Jul 7, 2009

clears bits M501-M0525 (uses 32-bit MOV instruction to clear 6 nibbles or 24bit starting from M501)

panic mode · Jul 7, 2009

right click on your program and choose "list of used devices", type M500.
you will see that bit M500 is not used but the higher bits are.
then right click and select cross reference and enter M501 (first used bit). you will see that there are shift and dmov instructions that manipulate your bits. get instruction manual for your plc (check download section of MrPLC.com if you can't find closer server)

Problem to understand mitsubishi PLC logic

mraj2001

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geniusintraining

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Viks

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Sergei Troizky

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mraj2001

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parky

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Topcat

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geniusintraining

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panic mode

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mraj2001

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mraj2001

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mraj2001

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mraj2001

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panic mode

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panic mode

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