Resetting counter at midnight when a machine is off

helphelphelp · Feb 19, 2020

Hello,

I'm trying to program a machine to reset a counter at midnight. I can do this no problem but I have a question about what will happen when the machine is powered off.

I currently have the counter set up to reset when the clock strikes midnight. When hour, minute and second are all 0, the counter resets. If the machine were to be powered off for some reason at the time the machine resets, unlikely but not impossible, the counter would then not be reset because it never sees the hour, minute and second hit 0.

Is there a way around this? Is there another condition I can add to reset the counter after powerup if it's a new day?

Thanks for the help!

Cheers

JesperMP · Feb 19, 2020

Welcome to the forum helphelhelp.

Which PLC ?

helphelphelp · Feb 19, 2020

Sorry I should have specified, it's Allen Bradley using Studio 5000.

jimtech67 · Feb 19, 2020

can the counter reset on power up ????
there should be a 1st scan bit

CommissioningMan · Feb 19, 2020

What are you trying to achieve with the counter? Perhaps you are better suited looking at system clock values. I believe it's called GSV in A-B speak.

helphelphelp · Feb 19, 2020

It can reset on power up, but only if it didn't already reset at midnight if that makes any sense. It's to be reset once daily after midnight.

peter764 · Feb 19, 2020

helphelphelp said:
It can reset on power up, but only if it didn't already reset at midnight if that makes any sense. It's to be reset once daily after midnight.

Can you just use the midnight hour to reset your counter with a oneshot? This would give you an hour to reset your count in case the machine is powered down? Still no help if the PLC is down over an hour though?

helphelphelp · Feb 19, 2020

That is an improvement for sure.

EDIT: However that could be a problem if the machine is power cycled more than once during that hour.

jimtech67 · Feb 19, 2020

when the counter is reset buffer the day & time...
then at power up compare current date to the one that was buffered...

peter764 · Feb 19, 2020

helphelphelp said:
That is an improvement for sure.

EDIT: However that could be a problem if the machine is power cycled more than once during that hour.

Never though of that. so add another counter and reset that one when not equal to midnight...…...and add that counter to your original reset rung with the an equal to 0 on the accumulator of the new counter?

CommissioningMan · Feb 19, 2020

Something like:

Code:

IF currentDate <> lastResetDate THEN
   nCounter := 0;
   lastResetDate := currentDate;
END_IF

peter764 · Feb 19, 2020

CommissioningMan said:
Something like:

Code:

IF currentDate <> lastResetDate THEN nCounter := 0; lastResetDate := currentDate; END_IF

Great answer!

helphelphelp · Feb 19, 2020

Awesome thanks everyone for the help.

JaxGTO · Feb 19, 2020

AB has free download AOIs for comparing dates and times. You can get results from years to milliseconds.

janner_10 · Feb 19, 2020

If it's that critical, just get a cheap 24v UPS just for the PLC, it will stay on even if the machine is turned off, unless of course you leave it off for months on end!

Resetting counter at midnight when a machine is off

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