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Timer On (TON) not working after re-enabling communications to VFD


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I have an application where the PLC/HMI is talking to VFDs in the native UniLogic hardware configuration.

I have timers in my application that work fine initally; however when I turn off the 'Enable Communication' bit in any VFD instance and then turn it on again - none of the timers work properly!!

I can watch the timer current value counting down and it is nowhere near the real-time value.. Is seems very buggy to me.

Has anyone experienced this? Can a Unitronics engineer have a look into this at all?




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  • MVP 2023

Just out of interest, what happens to the scan times during these changes?

cheers, Aus

edit add after Flex below.   The reasoning behind the question is that it is possible that although the count looks regular on the screen, it may be that in fact it is being stopped then started every scan/few scans due to some other factor that is working on/off repeatedly.

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Hi Guys,

Yeah the routine containing the timer is called un-conditionally.  This bug is effecting every timer in the project..

It shouldn't matter if the subroutine is called un-conditionally or not; when the timer is enabled the processor 'tics' should be being used in the 'TON' instruction to account for discrepancies in cycle time - there seems to be an issue here..

I am using 1.29.111 at the moment - their tech support guys have asked me to go to the lastest (1.30.52) which has come out in the last 2 days so I'll give that a try & let you know about cycle times.




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