"Tim R" wrote in message
...

Worked at a plant that used Allen Bradley PLCs.

The program resided in memory but there was a backup EPROM in the cabinet.

You could also type it in by hand but it was thousands of lines of ladder
logic, any line of which could point to any other, it would take weeks.

So we lost the program in a power surge or something. No problem, pop the
EPROM in and download the program.

Meanwhile the production manager is screaming we're going to miss the ship
date and lose the customer. No sense of humor, those guys.

Here's the catch: on some PLCs download the program means install it FROM
the EPROM, but on these A-Bs download meant install it TO the EPROM. So
we downloaded the empty program into the EPROM, erasing it.

No problem, we have a spare safely locked in the maintenance office.
Notice I said A spare, as in, one. You already know what we did, popped
that one in the PLC and erased that one too.


We had about 40 or 50 of the AB PLC 5s in the plant. Some of the older
ones. Just glad that they finally came out with some computer software that
could be loaded on a laptop, and then later it was on a network where we
could sit in one room and look at most of them. This I hated about the ABs
were we were suspsoe to power the thing down if changing out an input or
output card. When running a continious process 24/7 we did not want to shut
down a PLC rack.


I liked the Fisher/Provox stuff much beter. We could hot swap any one crd
at a time without shutting off the other sutff.