SLC losing its place.

[Christoff84]

Hey all,

Recently one of my SLC 5/04's (L542B) has started losing its sequence when it's powered off. Until recently the system could be powered down and back up again without issue. I've looked at all the coding and the areas effected are all latch/unlatch instructions.

This is really stumping me, no program changes have been made to this area of the program and other PLCs in the plant don't seem to lose their place. We are in an area extremely prone to power outages and surges so this is coming somewhat of a severe issue.

Any ideas?

 

[RichardB]

Christoff,


There is usually a battery that keeps all the stuff when the PLC's are powered down.

Check out this thread with a guy having the a similar issue:

http://www.plctalk.net/qanda/archive/index.php/t-27474.html

Good Luck,

Rich

 

[Christoff84]

Thanks for the link but I don't think the situation is the same. The processor has not once lost its memory or had a major fault, it just seems to lose it's place in the bit logic. There is no EEPROM in the processor so I know the program is not being lost.

I know back when I was learning PLC5, there were settings for each N/B/etc file as to how it behaved when a power loss occured. You could set it to protected or redundant or something that would cause it not to be reset on powerup. Is there a setting such as this in a SLC?
I will have our electrician double-check the grounding on the plc tho.

 

[baxtersdad]

I have had similar problem which was resolved by replacing the power supply. Just a thought..

 

[keithkyll]

Frequently when electrolytic caps fail, they get high leakage. The visible symtom is they get hot. They still work somewhat when hot, but are way out of spec when cold.
This creates the symtom of "It stars working after it warms up". The only thing in today's electronics that starts working after warmup is electrolytic caps.
Follow baxtersdad advice and replace the power supply. That power supply is going to totally fail very soon.