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  1. #1
    Join Date
    Jan 2012
    Posts
    147

    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
    525
    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
    496
    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
    163
    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.

  6. #6
    Join Date
    Sep 2013
    Location
    Green Bay, WI
    Posts
    37
    Quote Originally Posted by kontrolthis View Post
    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.
    Sorry old thread. If your PID is in a hybrid activity this would be very easy to do in the state tables.

    Easiest way to add a PID with hybrid activity is by doing a side loop. Automatically adds it to the states table if you select it that way.

    Then edit states table. Right click add table select bool or enum. Have that table put your new PID block in hold if true.

    Then create new activity block and add your custom logic to hold the PID. After that connect to the state tables. Only take about 10 minutes.

    Hope that helps.

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