MI Values Being Reset To Zero

[active]

Hi All

Has anybody had the following issue losing MI Values in programs all reset back to zero for no apparent reason

have not set MI to change to zero on power up have cycled power numerous times on plc doesn't do it, not anywhere in programs am I resetting.  Happening at 3 different sites, completely different programs. One site happened 2 years of running fine after install.  One was running off of generator supply.

Only happens to MI that are either keypad entry or used to manipulate data in the program.

Using switch mode power supply to power plcs, have replaced backup battery even though not getting battery low alarm SB8

Still happens - only common thing across sites is that they are either out in the country or at a  mining site powered by generator.

 

[Joe Tauser]

I've seen that mysterious hiccup on remote systems.  It happens very rarely, but once is enough.  I've also seen inductive spikes caused by large contactors or other devices find their way via I/O wiring into the PLC and cause it to reset or the watchdog timer trip.

Do you have any power line filtering installed before the PLC power supply?  Is your low voltage and high voltage wiring adequately separated?

Joe T.

[Ausman]

Everything Joe says, and I'd also be having them go over all their earth connections and clean them up/check resistance.  The 2 years ok place reeks of something slowly drifting off ideal and your locations imply dirty environments.

On 04/02/2017 at 3:19 PM, active said:

Only happens to MI that are either keypad entry or used to manipulate data in the program.

So all the other MIs stay ok?  That is a strange thing.  Do they do it when adjustments are being made or just whenever? Have you tried disconnect/reconnect all the ribbon connections in the plc system, too?  Even internal ones etc?  Is the front membrane still ok?

cheers, Aus

[Simon]

I agree with all of the above - sounds like "dirty" power.  Another place I have seen this type of behaviour is on vehicles, where the PLC is directly connected to the main electrical system.  When starting the engine the voltage dips way down, and vehicles have a lot of spikes from the operation of the battery charge regular and large auxiliary loads.

Since you already have a switch mode power supply, which will be filtering out some of the transients and fluctuations, the next step in that direction would be a small UPS, either on the main side or the 24VDC side.