dobut in plc

i am having slc 500 series allan bradly processor and Rslogix 500 software. every month in particular date and time my processor is getting faluty and all of my plant getting tripped. is there any bug created by programmer for this sort of action or is it from some operation commands?

Maybe I am way off, but I've seen a network crash happening at regular times. The problem wasn't the software but a train passing close to the building! Really!
Actually I didn't see it myself but a programmer told me....

kannan,

when the PLC goes into fault mode, go online with RSLogix and examine S:6 "Major Fault error code".
Under Processor status .. Errors you will find a description of the error code.
With that info you can decide what to do (or ask on this forum), otherwise it will remain a mystery.

If you have a 5/03 or better and it is indeed the same day every month and the same time of day, search your program for S:37 through S:42 and see if they are used in any logic. In theory it is possible for someone to program logic that will throw the CPU into a fault at a certain time. Why they would do that I know not.

I had a similar problem like this a few years ago. Bit S:5/0 math overflow was being set after a multiplication and division. We checked the math several times but could find no reason for the bit to be set. It faulted the processor and shut down the system, several times. I found that in other programs, the designer would add a simple S:5/0 unlatch bit to the ladder logic to prevent this from happening. I had the same problem on a Micrologix 1200 last year, with no obvious way to cause an overflow, I added the unlatch for the overflow bit in it and have had no more problems.. If you have several math problems in the ladder you can put the unlatch at the end of the program, last rung.. If it's happening at exactly the same time, you might check to see if there's some math involving the real time clock.