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What does "PID" stand for?

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  • What does "PID" stand for?


    I have Googled it, but everyone just uses the acronym / abbreviation. I haven't seen it spelled out in complete words as a phrase.

    I have a "PID" on my new Rocket Giotto v3 behind the drip tray. This PID shows water temperature. (I think at the group head? Or is it temperature at the boiler?)

    Apparently these things are called "PID / SSR". "SSR" I think means "Solid State Relay"?

    The PID is not a "pressure indicator" - because it's showing temperature.

    There are two other dials that indicate pressure. One dial presumably indicates boiler pressure. The other pressure in the group head?

  • #2
    PID controller - Wikipedia, the free encyclopedia , second result of 101,000,000 from a quick Google search.

    I'll let someone with more knowledge of the Rocket Giotto v3 answer your other questions.


    • #3
      Thanks. Silly me. I googled "PID/SSR" - not "PID" - so didn't get the Wikipedia result. Should have checked there first, but I'm lazy and forgetful.

      "A proportional-integral-derivative controller (PID controller) is a control loop feedback mechanism (controller) widely used in industrial control systems. A PID controller calculates an error value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process through use of a manipulated variable."

      Hmm. Now I know what "PID" stands for, at least. I'm not sure I know what the PID on my machine is doing, or how it's doing it. The fact sheet on the PID provided by Rocket is in very strange language that resembles English somewhat.

      I gather that it's measuring water temperature at the boiler, then inferring (?) what the temperature at the brew head will be, probably based on measurements taken with the SCASE Thermofilter that they refer to.

      If the PID reads 120C, then I should be getting 93.6c at the brew head. It says. I'm sure they're right.

      So much to learn.

      Thanks for your reply.


      • #4
        A PID controller is a device which compares an input value (say temperature) to a setpoint (what you desire the input to be) and determines if it should increase or decrease the output (say, percentage of time the heating element is on), based on a calculation. The calculation uses the current/proportional error (the difference between the input value and setpoint), the integral error (the sum of the error over time) and the derivative error (how quickly the error is changing) as input.

        They are used in many other applications (such as robotics or chemical process control). The calculation is generally the same, only the input/output variables and the coefficients (the PID settings) change.

        There is a great introduction to PID control written by Brett Beauregard who wrote the Arduino PID library.


        • #5
          A traditional thermostat controls temperature by turning on full element power at a certain temperature (e.g. 115 degrees) then off again at a higher temperature (e.g. 125degrees).

          A PID controller is able to pulse/apply less than full power to the element to maintain a specific temperature (e.g. 120 degrees)

          In your case, if the temperature of the PID temperature sensor is at 120, then the water at the group head will be about 93.6 because of the machine design- the PID doesn't know this, it's just maintaining 120 very accurately.


          • #6
            I have a Breville Dual Boiler BES900. The BDB maintains temperature stability, at the brew head, to within 1 degree of the set temp with two PIDs. One for the brew boiler and one for the brew head where it controls an extra heating element.



            • #7
              Originally posted by Barry_Duncan View Post
              The BDB maintains temperature stability, at the brew head, to within 1 degree of the set temp with two PIDs. One for the brew boiler and one for the brew head where it controls an extra heating element.
              Yup! that's a great feature. AFAIK. almost none of HX machine has PID for group/brew head (due to the E61 group design already providing a very predictable temperature). But some extreme DB does get one!