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How do PID temp controllers implement control

  1. Dec 2, 2015 #1
    My group members and I are trying to build a snow heating mat. So far, we are using nichrome heating wires sandwiched in silicone rubber connected to an arduino that controls a solid state relay to turn on and off electric current from a wall plug. What I want to know is how to control the temperature. We decided to stick with an on and off control since it's the easiest to work out but I want to know how you implement a P or PID control. Do I need like a variable resistor or something? Or what way is the PID control supposed to vary the power output?
  2. jcsd
  3. Dec 2, 2015 #2


    Staff: Mentor

    I don't think PI or PID is justified for something like that. A simple proportional control wi a dead and will do.

    You need the dead and to prevent it from cycling endlessly.
  4. Dec 2, 2015 #3


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    Science Advisor

    Here is the arduino PID library:

    Here is an example using the library with a relay:

    Background on the development of the arduino PID library:

    Some background on control theory:

    If you google "arduino sous vide" you'll get many results where a relay, heater & PID* are used together with an arduino to maintain a temperature setpoint.

    *While a PID controller is used, I & D are set to zero so it's P only. like anorlunda recommends.
  5. Dec 2, 2015 #4
    What's a dead and. and is it safe to use a proportional control with a solid-state relay
  6. Dec 2, 2015 #5


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    Science Advisor

  7. Dec 2, 2015 #6


    Staff: Mentor

    With on-off control, you need deadband to prevent endless cycling. With deadband, you can't use integral control, because that would cycle.

    All you need is two statements. Let T be temperature, P set point, and D deadband.

    if P-T > D then turn_on;
    If T-P > D then turn_off;

    D is your only tuning parameter.

    Good luck.
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