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Ran into a weird issue.

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I have a pump that is controlled by timers. It is a ~4gall on/minute pump. We calibrated the value so when I enter 6 liters it converts to 25.2 seconds.  Then I store this to an ML and that ML to the TA timer by ST TC.   Using a flow sensor to make sure there is actual pumping going on.  Once the chemical is pumped in the TA timer is 00:00 and it goes to the next step in the process. When the process is over I reset the system by store the preset 6liters to the ML and the TA timer.  All this works great, but every couple weeks the TA timer coil stays on even after I stored the new value to it. If I install a reset coil for the timer then it wants to reset to the preset time (in the timer creating window) not to the ST TC. I can't use a TD timer because if during the pumping I have to stop the machine, it would reset to the full amount. I want to continue from the remaining time like all TA timers. 

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  • MVP 2023

Edit much later........I completely missed that you appear to not have a reset coil at all.  However,  the comments essentially remain the same.  I'll also throw in that I generally try to not have a physical output being run in an inverse state from what directly controls it, which is what you must be doing here.  I'll also add that your best method would be a flow rate system, not a timed run.  So much can vary mechanically on a timed run.

I would guess that the timer is staying on because the reset is somehow being missed, could be a "missed by one scan" or similar situation.  Note that TAs need the reset to turn off.

One solution would be to store your values into other operands, and then reload from themnot the originals.  This way you can also update your current timer value to your stored area to have available if needed.

However, before doing anything, perhaps put in a few scans delay b/n the timer elapsing and doing your resets.  Check that the timer has reset as expected, and if it hasn't, do the reset again. Perhaps even split all this up into a few scans as well.  To me it just sounds like a scan overlap issue, but as to why it only does it occasionally....who knows.  So....check the desired action has actually occurred, do it again if it hasn't, and then  do all your initial storing.

cheers, Aus

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I did have a reset coil at first, but it reset to the preset time in the timer creating box. So if it was 25 sec but the stored MI was 40 sec the reset coil overwrite the the stored MI. I've removed the reset coil and it worked for weeks, then acted up, then it was fine again. Sometimes just a simple power cycle fixed it. Weird. 

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  • MVP 2023

Maybe TA reset coil in help  recommended rung is in wrong position or not present (see red and arrows). And some condition not activate timer reset.



I sometimes need to build time controlled application with interrupt by PAUSE button.

Then State Machine used.

But i do not use the timer. I use SB15 (SB13 for seconds) and increment some MI or ML. This MI or ML is presetted by STORE direct function at step before time controlled  step.

If incremented value is reached i go to next step. PAUSE bit used for stop increment process and off step contolled output.

Then state machine can be paused in time controlled step without time lost. Sometimes i must Add or Sub to interrupted "timer" value some amount of "time" for compensate machine restart  delay.

Maybe this idea is not accurate but it work in many applications.    



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