Protected Instruction

Good day all. I would like to know if there is a way to protect an integer word address in my PLC-5. Case-in-point: We have an interlock that prevents a Hydrogen valve opening until the retort temperature is >/= 1,432-degrees F. For troubleshooting purposes one of my co-workers set that interlock to "0" so he could test a new mass flow valve. You can probably finish the rest but I'll write it anyway. He forgot to put it back and I didn't notice it until today, 3-weeks later. So for 3 weeks one could have turned on the Hydrogen at any temperature, which given the right circumstances wouldn't have ended well. Is there a way that I can protect that word address so that once someone leaves "test edits" that it will not allow them to "assemble edits"?
Thank you.

Quick fix is to use a timer that after, say 10hrs, puts the original value back.
That way it can never left.

Greg Fowlds said:

Quick fix is to use a timer that after, say 10hrs, puts the original value back.
That way it can never left.

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Interesting, would you happen to have a rung or two you could show me. I know how to write timer instructions, however, getting it to change an edit back to its original state, I'm not sure where to begin. Thank you

ceilingwalker said:

Interesting, would you happen to have a rung or two you could show me. I know how to write timer instructions, however, getting it to change an edit back to its original state, I'm not sure where to begin. Thank you

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Instead of a constant value (which needs an "edit" to change). Use a register
with the value you want in it ( "Edit not required to change value). Then the above timer method will work, with a "MOV" instruction.

think about just sounding a horn (etc.) if the value isn't where it should be after a certain amount of time ...

I'd be worried that just automatically moving a value (even the RIGHT value) back in all of a sudden could throw a monkeywrench into somebody's testing or troubleshooting operation ...

I know I wouldn't want that type of surprise ...

Mickey said:

Use a register
with the value you want in it ( "Edit not required to change value)..

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What is a register and how do you use it?

"register" is just another way of saying a "memory location" - such as N7:54 - or F8:2 ...

Allen-Bradley doesn't use the term "register" very often - but many other manufacturers do ...

I've never heard the term used to refer to just ONE bit ...