mitsi m8000 device

delph · Sep 21, 2002

can anyone tell me in basic terms where and why the device m8000 is used thanks

Eric Nelson · Sep 21, 2002

M8000 is the "RUN" monitor. It is ON when the PLC is in "RUN" mode. What is a good use for it? You got me... There's probably a good reason why it exists, but I can't think of anywhere within the program where it would be "needed", mainly for the fact that if it is OFF, the program won't be running to check it...

Perhaps it can be used by other PLCs on a network to determine when this PLC is in run mode?

On the other hand, M8002, which is similar, but only turns on for 1 scan when the PLC enters "RUN" mode IS handy. You can use this to run any "housekeeping" logic at initial startup.

beerchug

-Eric

Goody · Sep 21, 2002

The special relay M8000 is an 'always on' bit.
There is no predefined use for it, it is a tool to be used as you see fit.
The coil of M8000 does not need to be driven as it is always on. You usually use the N/O bit to permanantly drive something else.
Typical examples would be:
To drive other special relays that, for instance, alter the time base of timers or change certain counters from up to down counters.

Or something that must happen on power up, perhaps a warning light or sounder that warns that the machine is back on.

x · Sep 23, 2002

Used mainly with older MEDOC software, this BIT was very commonly use first in the rung. This way it was easy to insert another condition in the rung. With the DOS software it was hard to do so unless you where editing in sequences.

Eric · Sep 25, 2002

I realise that any unused M coil could be used but if one uses M8000 to set things like M8028 to set times above T31 to 10 ms then it can be seen by any other user what you are doing but if you never set lets say M0 and use |--|/|---------(M8028)--|
M0
Then it is possible that this does not stay set.
I have missed removing unused --|/|-- and found although it was no where else in the program it still became set. We assumed it was due to welding on the machine but no way to really find out how it became set.
But I can't see why I would use M8001 why would one need a contact to say PLC not running?

All best Eric

Goody · Sep 25, 2002

can't see why I would use M8001 why would one need a contact to say PLC not running?

It doesnt actualy say it isnt running. It is a contact that is always open while running.

This can be used at the beginning of some code that you do not use in the main program. Say for perhaps error trapping.
A routine you write but only use when fault finding. (You change the bit for another while using your routine)
If you used a unused internal relay, later on it might be used by mistake in some additions.

bvpkr123 · Nov 1, 2012

Nc m8000

When we use NC M8000 contact?What is the use of it?

Sergei Troizky · Nov 1, 2012

For an external device communicating with the PLC, M8000 is the PLC Run mode monitor.
From the PLC program point of view, it is "Always On" bit, as the program is being executed only in Run mode.
It is used for unconditional rungs, as the Mitsubishi syntax requires at least one contact in a rung.
Also, it may be used as a plug , as the Mitsubishi syntax does not allow shorted branches.
The mentioned syntax limitations are properties of the PLC, and do not depend on the programming software used.

bvpkr123 · Nov 1, 2012

Actually i am asking about the use of Noramally closed M8000, when this contact is use?

Goody · Nov 2, 2012

This original post is 10 years old and all the answers you could need are written above.
There is no defined reason to use N/C M8000 but you could if you wanted.
If you are struggling to understand all the answers above might I suggest a new career direction.

bvpkr123 · Nov 2, 2012

I understood all the posts, but it is not mentioned the use of M8000 NC contact.But now i found out practically.M8000 NC will be ON when PLC is in Stop mode.One application of M8000 NC is it can drive reset relay.

Sergei Troizky · Nov 2, 2012

NC M8000 cannot activate anything, simply because it is always Off.
It may be used only to forbid execution of the further logic in a rung or branch.

dantut · Nov 2, 2012

A N/C M8000 would not execute the right side of the rung. Sergei is correct - it will never run.

At times I have used it as an Open M8000 to reset a block of data for a new project & then change it to a N/C M8000 when I dont need to do that rung anymore. It should really be removed from the program when not being used.

mitsi m8000 device

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