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PAUSE the running program

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I am making a machine, where, for safety porpuses I need to PAUSE the program. My machine has a Pressure reducing valve and some solenoid valves. If my pressure sensor senses that pressure is too high (my  Pressure reducing valve doesn't work correctly for example) I just want to pause my program so it doesn't open any solenoid valve and let that high pressure into my machine. So is it possible to pause a program untill pressure is too high? Including pausing Timers so they wouldn't count. Program is written in Visilogic.

Thank you, Jan

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  • MVP 2023

No, it is not possible to pause a program.  You're not thinking in Ladder Logic. There is a Watchdog Timer that will shut you down if the program does not execute continuously. What you must do is write your program so that when the pressure goes too high the correct actions are taken, such as preventing valves from opening. Pausing timers is a different issue. Only an Accumulating timer can be paused. Depending on what you're doing, if you need a timer to be paused, a timer may not be your best option (maybe a counter would be better). Though it is possible to Store and Load timer values if needed.

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  • MVP 2023

As Flex points out, a ladder program is designed to continuously scan.  You can use this to your advantage, as you don't want the PLC to go dormant in some kind of PAUSE mode and ignore the rest of the conditions on our machine.

1.    Make a high pressure alarm bit and block your solenoids with it.  You may or may not want to make it self-resetting, but you'll want a deadband so it doesn't chatter.  Block your solenoid outputs with this bit.



2.  I often roll my own timers when I want more control.  Use one of the internal system time pulses and an MI to count them.  Then you can use the alarm bit to "pause" the timer without loosing it's place.  Note that you'll have to handle resetting it.



Note that these are very basic general examples.  If you start asking specific questions about your program, please upload your .vlp file so we can see it along with your questions.  Posting a bunch of screenshots usually doesn't tell the whole story.


Joe T.




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