Program Logic Control Trouble Shooting

Is the 'input instruction' going to the right address?

I think that you should determine why the input instruction changes to false.

That would entail troubleshooting the control circuitry as instructed in the operator's manual or on the manufacturer's website. The telephone is always an option, though seemingly little used.

You can check the relays and fuses and run through the troubleshooting and report back after that is resolved.

Is this a new problem?

One possibility is that the output circuitry is an AC Silicon Controlled Rectifier (SCR) but your motor is uses DC power. Since an SCR will only turn OFF when the current goes to 0, it will not turn OFF.

You may have also been hacked by some Russians. [Don't tell Vladimir I said that.]

What voltage is there across the motor relay coil?

Welded motor relay contacts are possible; it is also conceivable (though perhaps less likely) that a PLC output relay may be stuck closed.

I would reboot and see if it stops....If it does then your program may be corrupted, or conflicted....

That circuit diagram is totally nonsensical.

I know, that's a sort of null hypothesis to be proven true or false.

They use some sorts of those in the academe, sometimes in licensure exams. People tend to see faults better than credits, you know. I hope the OP realize my point with little imagination.

Probably would have been clearer just to post "Did you wire it up right?".

"That circuit diagram person is totally nonsensical."

OP should listen to others on this forum, and reset the PLC.

OR he could look at the ladder rung that is supposed to either activate or deactivate this motor, and install a bit trap around it, or he could just see if the panic button is faulty, or if the panic button shows up on the PLC once depressed?

I show up as depressed all the time.

With so little information to go on all we can offer is guesses.

Is this a new installation, existing installation that has stopped working properly or a school project? What software and PLC (or similar) are you using?

I am assuming that the e-stop state changes from true to false to indicate it has correctly changed from closed to open state, and that this is not a software failure flag (or similar).

Check the software logic and output to the contactor and the contactor itself, chances are it will be one of these things that is the problem. Let us know what you find.

Information furnished by you are not sufficient.

Is it latest development,or commisioning problem.

If it is latest issue, then the program would have become corrupt.

Reload the program into PLC and try.

Disconnect the power connection to the motor and try the sequence .

If the program is good, for stop signal the power contactor should drop ,instead of pick up of some relay.

Unless we see the ladder diagram , we can not give you any more cooments.

A1) It is not possible to say, as the problem cannot be seen from here.

A2) A telescope is unlikely to prove as effective as hiring a local Consultant to look at the problem and solve it, as self-determination seems to be ineffective.

Troubleshooting is very easy, once you determine how the sequence is to function. Once determined, follow the sequence as it is to occur and see where it doesn't function as desired.

So first you must determine what pushing the "stop" button actually controls. Does it cut the power to a relay/contactor? Does it instead input to a PLC, which is supposed to control relays/contactors ?Does it trigger a safety relay? Is a VFD or soft start involved that may be PLC controlled or directly controlled from the stop button?

Find the stop sequence order and what components are involved in this sequence.

Consider as well that perhaps this particular motor is not to stop under stop conditions. I didn't hear any mention of "emergency stop", so something, such as a cooling fan, continuing to operate may be a normal operating mode.

If the stop sequence actually is supposed to stop the motor, then determine what component in the sequence has failed, such as a relay or contactor, or the output from a PLC card, if the stop does not directly control the motor contactor or relay or VFD.

While probably not related, this post reminds me of a problem I had with a PLC recently. The PLC with relay outputs had functioned without a problem for a number of years. The panel containing the PLC had just been modified to mount a display by cutting an opening using an abrasive cutting tool. After the modification, one output would not turn off when the program logic turned it off. This was verified by monitoring the PLC with my PC. However, when the PLC power was cycled from off to on, the output stayed off until the logic turned it on. After that it remained on regardless of the logic. As this was a small, inexpensive, "brick" unit, I replaced it with a new one, and all was good.

I examined the problem unit and discovered that metallic dust from the machining operation had entered the case through the cooling vents. Apparently some of this dust had created a high resistance bridge on the circuit board at that relay.

The resistance of this bridge was high enough so the the current was not enough to pull in the relay, but once the relay was energized through the normal circuit, the leaking current was enough to hold the relay closed.

Geez what a pain that must have been. Thanks for sharing.

I had one problem not entirely unrelated a while back, where the programming genius that was hired on contract by the OEM vendor, came in and and just did a bunch of copy and paste between A and B redundant sets.

Then he forgot to change the pasted A's to B's, or was it pasted B's to A's? Anyway, one of the ORP outputs was shown on HMI screen to be correct about half the time, when the other ORP was below the allowed range, and the control level indicated it was going off half the correct value. We finally found the bug and eliminated it with Fernando bug off spray (call it changing labels to match the rungs).

The only worse problem to have is undefined global warming. I hate those undefined globals when they sneak into the microwave!