Controllogix missing logix scans?

albeard

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Nov 2010
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Courtland, ms
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I have a data collection application in a controllogix 5561 which pull data via msg from other processor and then does various calculations, etc. At the top of the hour it move data from current hour words to previous hour words via a one shot bit in the continous scan program that then cascades through the other ladder programs that are called through JSRs. At random times, it simply doesn't make the move, as if the one shot bit didn't take place. Happened 3 hours in a row yesterday and when I started watching it its worked fine since. Has happened several times over the last 2 weeks at random times and no specific time of day. Any ideas what I could be doing wrong here>
 
robertkjonesjr said:
How do you test for top of the hour? Could you be missing it?
Click to expand...

Beat me to it.

We would need to see the rung to have a real suggestion. I have several applications that work on similar principal that you describe and it does not seem to have the issue you describe.
 
welcome to the forum ...

can you post your complete ACD file as an attachment to this thread? ... (you'll need to ZIP it first) ...

there are a lot of possibilities here ...

quick question: what conditions do you have to the left of your one-shot? ...

I assume (gosh I hate that word) that you're using a GSV instruction to bring in the processor's date and time ... how often does the GSV get executed? ...

having your ACD file would help a lot ...
 
I setup 2 DINT arrays to move Realtime clock into
CLOCK[] AND CLOCK2[]. First move Realtime clock to CLOCK2[], then compare NEQ CLOCK2[3] TO CLOCK[3] to see that hour has changed and set BITS[1] to true via a ONS. Then move realtiime clock to CLOCK[] in that order in logix. Then use BITS[1] to trigger data moves through the rest of the logic. BITS[1] should be true for one complete scan of the program and then turn off.
 
OK, if you do some deep research I think you will find that the GSV statements may take longer than one scan to complete and you are using TWO different GSV statements to fill Clock and Clock2 arrays (not quite what you described above). Do what you described above and it will work.

For the WALLCLOCK object I doubt that takes over a scan, but the point is that these instructions do not necessarily complete when the logic engine exits that rung and can be non-deterministic the way it was used.

Darren

When I say do what you describe above I mean to only use GSV for one of the clocks and then after your compare then do a COPY to the secondary clock.
 
Last edited:
That's interesting that it would take more than one scan to GSV the clock to the array. So you're saying should GSV once to clock2[] then after the ONS use a COP to move clock2[] to clock[] rather than separate GSV's?
 
Yes that is what I am saying.

Also I edited my statement. I was exaggerating I am sure and you are right, I doubt the wallclock object requires more than I scan. The big issue is that it can be non-deterministic the way it was used.

Darren
 
The DTR instruction handles both the one-shot and differential compare easily.
This is my typical bit of logic to generate a global one second pulse, but can be modified obviously for hourly/daily, etc...

XIC GL_100MS_Pulse BST GSV WALLCLOCKTIME  LocalDateTime PLC_Time[0] 

NXB DTR PLC_Time[5] 255 Sys_Old_Seconds OTE SYS_One_Second_OS BND



Note that I only bother querying the Wallclocktime element approximately every 100ms (based off of a free running timer), as it's not needed to do it every scan.
 

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