An inconceivability event of PLC ???

[FQ-ONG]

Hi All,

We face to an enigmatical event of PLC.

This PLC had operation in good condition for 10 days before this enigmatical event happen.  Suddenly, the PLC switch off all the I/O, reload the program and turn on the I/O. After 2 minutes, PLC repeat this few step again. Its frequently happen in two minutes time without rhyme or reason.

After that, we transfer a BLANK program into PLC, that few step switch off and on the I/O was not happen again. After monitoring in one hour, we transfer back the original program into PLC, and it also doesn't have any abnormity happen untill now.

Before this abnormity happen untill it operation back to good condition, all wiring for I/O, analog I/O, power supply and RS485 unchanged and no unpluged.

Does anybody have an experience with this event before?

Our customer request: "Please investigate the actual route cause to eliminate the problem to the future. Please narrow down to the detail."

Thank You,

Regards,
FQ
 

[support]

It sounds like a software related issue. There are two possibilities:

1) An I/O condition causes the program to enter a dead loop somewhere in the code which triggers a watch dog timer reset. The condition is not repeated after you have transferred the blank program and then re-transferred the original program and the PLC no longer run that part of the program

2) Some part of the EEPROM program is corrupted by electrical noise or serial communication command that changes the program code, which cause the PLC to execute a wrong program and resulted in watch dog timer reset.

[FQ-ONG]

Could it be solve permanently, or not?

[support]

It really depends on what is the cause and what triggers it. It may never happen again if the same condition never happen again.

[FQ-ONG]

How to avoid this happen again?
How to research what is the cause and what triggers it?

Thank you.

[support]

First place is to examine your code to ensure that there is no dead loop somewhere. E.g. an endless goto loop can result in a WDT reset.  

We have already supported you through email for this event in which you mentioned that removing RS485 connection and the problem stopped. It could be that an RS485 short circuit/ground fault that cause the PLC to reset.

There are many ways to cause an electronic circuit board to reset. The phenomenon you described (constantly reset every 2 minutes) does not point to a PLC hardware issue. There have not been any report of simular issue. Therefore we believe it is an engineering issue in which you have to investigate.

[FQ-ONG]

   Hey, I haven't solve my problem, how could you lock the topic!!!  

So, your conclusion for that cause the PLC to reset is hardware, software or both?

Would you like to help us to investigate and avoid this happen again?

Good Luck!!!

[evanh]

I'd like to point out your information is not clear as to what is happening now and what events happened when.

From what little I've been able to glean, it could be thermal shutdown of the 5 volt regulator.


Evan

[support]

 Hey, I haven't solve my problem, how could you lock the topic!!!  

So, your conclusion for that cause the PLC to reset is hardware, software or both?

Would you like to help us to investigate and avoid this happen again?

Good Luck!!!

I believe we have provided you with all the answers we can give about your situation, which we are confident is an installation/engineering or even just pure accidental and not a PLC hardware/firmware problem. This forum is meant to provide answers to "how to" of the PLCs products, not to solve individual engineering problem. On top of that you have been sending us lots of email directly and we've already answered every one of your email of the same topic. It become a double job for the tech forum if you are emailing while posting non stop asking for an answer that we are unable to give. Or to put it simply - we don't know EXACTLY what caused your problem. But we are very sure it is not a PLC's inherent design problem and in the earlier post we have already given you the suggestions  what we figure could be the likely cause based on your description, and short of flying into Malaysia to stay with your machine until it happens again, we can't be 100% sure what was the reason for something that happens once and then doesn't happen again.