bcalhoun (Customer) asked a question.

October 6, 2020 at 1:05 PM
Lead Lag programming. New PLC programmer here. I'm using a click PLC to stage and operate 2 fans with a 0-10vdc control. I have searched the forum and can only come up with legacy posts with bad links. Can someone help with a programming example?
  • 7 answers
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  • ssweber (Customer)

    Please explain a little more about your inputs/outputs and what the different steps you are envisioning.

     

    ie, are the fans controlled with 0-10v? What kind of voltage runs the fans? Do the fans respond to environmental conditions, or purely operator driven?

    • bcalhoun (Customer)

      The application is a Laundromat. The fans being controlled are to supply air to the the dryer area from outside to overcome negative pressure issues.

      I'm using 0-10vdc Current sensors on the 3 phase power supplying the dryers into the analog inputs of the PLC.

      I'm using math to calculate the sum of the 3 measured currents entered into a Y=mX+B linear equation to determine what the fan speed should be.

      The result is a 0-20 value that is entered into comparison equations for staging.

      If output is 0-5 then 1 fan at that value

      If output is 5.5-20 then 2 fans divided in half

      This controls 2 fans with ECM motors powered by 110v and their speed is controlled by 0-10vdc signals (actually 2-10vdc)

       

      I've implemented this and it appears to be functioning the way I envisioned it. I would now like to add Lead/Lag somehow and I'm not sure how to proceed as my output is not an on/off that can be

      easily entered into a timer or a counter.

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      • ssweber (Customer)

        That's a pretty neat setup! Honestly this is the first time I've been exposed to lead/lag terminology.

         

        So I take it you want 1 fan to go from 0-10, then the other one to kick on from 10-20? Or keep it the same way, 0-5, 5.5-20?

         

        If it were me, I would probably flip the lead on a daily or weekly basis. But maybe you want it to be smarter than that. I'm assuming it's number of starts that makes fans fail, faster than the speed you run them at, right? If you wanted to flip/flop based on hour-usage, you could also set some counter that initiates the flip after the lead fan has reached x hours.

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      • bcalhoun (Customer)

        Thanks, so far it seems to be keeping the air conditioning in the building where it should be.

        I want to keep the staging the same and do exactly as you suggest.

        I staged the fans that way because the relationship between airflow and speed is close to linear. The relationship between fan speed and energy expended is a 3rd power relationship.. Better to run 2 fans slowly than 1 fast.

        Your response made a light bulb go on in my head. A simple timer that resets after it gets to a certain value. I think I was over complicating things.

        Thanks for your Response.

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  • Garry (Customer)

    This post will show a sample program lead /lad pump.

    http://www.plctalk.net/qanda/showthread.php?t=63201

     

    Here are some additional links for reference:

    http://www.plctalk.net/qanda/showthread.php?t=22500

    http://www.plctalk.net/qanda/showthread.php?t=91902

     

    Here is some information on PID with the Click PLC.

    Click PID Control

    Using math to do the PID Control:

    https://accautomation.ca/click-plc-pid-using-factory-io/

    Using the PID Instruction in the Click

    https://accautomation.ca/click-plc-pid-instruction-and-autotuning-using-factory-io/

     

    I hope this help you out.

    Regards,

    Garry

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