strange behaviour in PLC

Question

strange behaviour in PLC

DTSFA (Electrical)

(OP)

19 Feb 13 16:10

hi

i have a PLC where the inputs appear stable,

but, the internal memory coils appear to be operating erratically ?

causing the output relay to operate in chatter mode for period of time, then no output at all, until PLC is re-booted.

( the PLC hardware has been changed, no improvement )

the PLC is programmed with flash device, we do hunch a small hunch that the flash device has become corrupted,

and hence the software program in this PLC is corrupt,

the DC supply appears stable, all inputs are digital,

does anyone have other experience, ideas ?

thanks

IRstuff (Aerospace) · Answer 1 · 2013-02-19 20:53:22

OK, so why aren't you replacing the flash memory?

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moggie (Electrical) · Answer 2 · 2013-02-20 02:02:56

What make/model PLC?
Are you writing to the "internal" memory more than once?

jraef (Electrical) · Answer 3 · 2013-02-20 14:09:40

If the hardware has been changed and the problem persists, but the program is the same, it has to be in the program. Sounds to me like an inappropriately implemented jump function or subroutine, something like that which is creating a conflict in writing the output image table. Some cheaper PLCs may not have a scan monitor to guard against this. The eventual shutdown would likely be the watchdog timer seeing that the overall scan was taking too long as the errors accumulate and turning off the PLC.

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strange behaviour in PLC