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  1. #1
    Join Date
    Jan 2012
    Posts
    146

    Using PCT, disabling PID

    Anyone know a good way to disable a PID loop while it's not being used?

    What I am trying to achieve is to not have a PID reaching 100% before it is enabled. if the pool WST = 25 deg Cbut my setpoint is 30 deg C, and they want to use the dry-o-tron as the primary heating, I want my PID to be at 0 until I get the command to run. When it runs, I want the PID to increase, rather than already be at 100% by the time it's required.

    The only way I thought about was to use a selection block, or perhaps switching it to reverse/acting.

  2. #2
    Put the PID inside a hybrid activity block. When the block is disabled, the PID will shut down. When the block is enabled, the PID will start to modulate from that point.

  3. #3
    Join Date
    Jan 2008
    Location
    Near Philly
    Posts
    512
    Quote Originally Posted by Questionz View Post
    Anyone know a good way to disable a PID loop while it's not being used?

    What I am trying to achieve is to not have a PID reaching 100% before it is enabled. if the pool WST = 25 deg Cbut my setpoint is 30 deg C, and they want to use the dry-o-tron as the primary heating, I want my PID to be at 0 until I get the command to run. When it runs, I want the PID to increase, rather than already be at 100% by the time it's required.

    The only way I thought about was to use a selection block, or perhaps switching it to reverse/acting.
    Check out the states tables, most likely something can be easily changed there.

  4. #4
    Join Date
    May 2003
    Location
    Connecticut
    Posts
    485
    I would just use a MUX to put the setpoint or input to a value that would make the pid go to 0

  5. #5
    Join Date
    Jun 2007
    Posts
    159
    On a similar thought (sorry small hijack) has anyone tried to freeze a PID when conditions are just right with a HOLD hybrid activity? I need to build a custom one.

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