Plc fault

Hello,

We have a PLC fault that is controlling a water treatment plant. The customer wants email notification if this is to happen again.

Can a micrologix 1400 and using RSLogix Micro Developer send A bit or something to the HMI if the PLC was to fault again ?

From there I can get the HMI to send an email.

Why would you not fix the problem that causes the PLC to FAULT??

Perhaps a modem through serial port and send a Text message?

Relying on a bit to be set still opens you up to the risk of the PLC dying completely. I normally use a heartbeat. Either an incrementing register that resets at 32000 back to zero, or a bit that toggles on and off every 2 seconds.

If the value remains static or the bit stays either 0 or 1 for more than a pre-determined time then generate an alarm.

And I'd be looking further for single points of failure... do both the HMI and the PLC run off the same power supply? Fed from the same control breaker? Then you risk both dying simultaneously and again... no alarm.

The error was some kind of mathematical error that resulted into a major fault.
The HMI did not lose power, and didn't lose connection to the PLC. The HMI was unable to write to the PLC but seemed to be reading.

That being said, would it still be recommended to do a heart beat instead of monitoring system word S:6 which is major fault condition

This PLC has been running perfectly in the field for several years. first time this happened, I cleaned the fault and seems good now

richleva said:

That being said, would it still be recommended to do a heart beat instead of monitoring system word S:6 which is major fault condition

This PLC has been running perfectly in the field for several years. first time this happened, I cleaned the fault and seems good now

Click to expand...

Yes, because the heartbeat failure will catch a number of other things (communication failures, power supply issues) that reading the major fault register won't.

The PLC likely faulted because an instruction divided by zero or a register may have overflowed.. It would be in your best interest to investigate the root cause so you can guard against it, otherwise it is likely to happen again.

I'd bet money the problem lies in some logic that is doing flow totalization.

One note the Micrologix processors have an issue with math overflow status if it is set when the program 2 starts at line 00 it will fault the processor. this doesn't happen with every scan an not even when the status bit is set so it could be set in line 1 but it wouldn't trip until the program 2 rolls over and restarts.
the solution for that is if you do any math functions in the program in very last line of the ladder code place an unconditional unlatch of the status bit or you can remember to reset the status bit after each math function.

Also any data received from a faulted processor is unreliable and should not be used
as suggested before set up a heartbeat monitor in the HMI if it fails to communicate or the heartbeat fails let the HMI send an email and post an alarm
you may b able to reset the overflow status bit and restart the program from the HMI if the operator in on site it may take a little thought to set up.