Negative Value loaded into timer.

[Operaghost]

There is actually a note in the Help that says to make sure the timer runs every 69 minutes otherwise the ACC won't be correct. Nothing about it potentially rolling over to a negative value and causing a fault. Just that "the ACC won't be correct if this happens".

Never noticed that before. I knew there would be accuracy issues, but didn't know what the magic number was. And like you said, I never put timers into these scenarios.

OG

 

[TheWaterboy]

There is actually a note in the Help that says to make sure the timer runs every 69 minutes otherwise the ACC won't be correct. Nothing about it potentially rolling over to a negative value and causing a fault. Just that "the ACC won't be correct if this happens".

Never noticed that before. I knew there would be accuracy issues, but didn't know what the magic number was. And like you said, I never put timers into these scenarios.

OG

Its conceivable that there were no negative numbers in my case. But I am not at all certain of that so it was worth putting out there. But they certainly weren't "Correct".
69 minutes ? I'm sure that has some significance related to the clock, 4140000ms . . . 22 bit register? Weird number though.

 

[rootboy]

I didn't know that either. But according to: 1756-rm003_-en-p.pdf

"IMPORTANT Make sure to scan the timer at least every 69 minutes while it runs. Otherwise, the ACC value won’t be correct.

The last_time_scanned value has a range of up to 69 minutes. The timer’s calculation rolls over if you don’t scan the timer within 69 minutes. The ACC value won’t be correct if this happens.

While a timer runs, scan it within 69 minutes if you put it in the following:
• A subroutine
• A section of code that is between JMP and LBL instructions
• A sequential function chart (SFC)
• An event or periodic task
• A state routine of a phase"

I'm with you, why 69 minutes?

 

[Bit_Bucket_07]

I'm with you, why 69 minutes?

Some ControlLogix developer probably thought that it was a cute ***ual innuendo Easter Egg.

 

[Bit_Bucket_07]

Really? That word is censored here?

Sorry if I offended anyone.

 

[rootboy]

Some ControlLogix developer probably thought that it was a cute ***ual innuendo Easter Egg.

That was the first thing that I thought, too...

It's still my "dummy" value that I use in my PLC.

As for offended, nope, never!

 

[TheWaterboy]

I always get all turned around when I use that value.