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Pid for temp control with ramp soak

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  • Pid for temp control with ramp soak

    I am having isuues understanding the process of the ladder logic for the p2k plc. I have used the click with great success for timers and counters. Very easy to understand. I am now trying to use the p2-550 with a relay output card and a thermocouple input card to control oven temp. Also using the c-more touch screen for user interface (i will deal with that later) I am having issues wrapping my head around just howw the pid function works and how to input the sv part of the pid. How the pid activates outputs below temp cuts them off at temp ect. I do have the temp reading in the ladder and active but dont understand where to output the pid and what to do with that once i do. Does anyone have an exmple of a working p2k ladder with pid control for oven temp with possibly a ramp dwell in it so i can see how this is supposed to work an get me pointed in the right direction. I have been struggling with this for 2 weeks. The youtube video has a video on pid control but fails to explain the output and its for a fixed sv so it uses a math equation to determine the sv . Please help


  • #2
    See Help Topic 167 in the Productivity Suite help file. Specifically look at the "Time Proportioning Control" towards the bottom of the help topic for your application. ( This is assuming you are trying to use the relay output card to control the oven temp.) There is example logic there of how to use the output to control an on/off output.

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    • #3
      so do i use the tag for sv to enter the set value? It has pid1.out for process output. what is the process for asigning that to a relay of the card?

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      • #4
        Yes, your set value is where you'd place the temperature you want.

        As the PSeries_Eng mentioned, you need to look at the help for the PID instruction (it may be faster to just go to the help to find the PID instruction, and get the explanation there. I've never been successful getting to the help I want through a topic number). Go toward the bottom of the new window, until you reach the program example of a balloon flying over a mountain, to get the answer you want. Your relay output, will be the "process output" shown in the program example. My only recommendation is, you should consider a solid state output triggering a solid state relay for powering your heating elements, as your relay output module will - due to the pulsing (on-off, on-off, on-off) of the output when it gets near the set value - eventually mechanically fail because you'll reach the cycle life of the relay quickly.
        If you've done the very best you can, worrying won't make it any better - Walt Disney

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        • #5
          Another thing, don't be intimidated by the values needed for the PID. The auto tune feature of the P2K has worked flawlessly for me. And what I found is, you'll only worry about P and I, and not use any D.

          In another thread, many found this document helpful.

          http://www.wescottdesign.com/article...ithoutAPhd.pdf
          If you've done the very best you can, worrying won't make it any better - Walt Disney

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