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    Dudes about Steinhart-Hart Equation

    Tuning and tweaking
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    • peirof
      peirof last edited by

      Hi,

      i d'like draw the funtion of Steinhart–Hart equation, for know how affects the pairs of T1/R1, T2/R2 and T3/R3, that are mi entrance dates, but i have two doubts.

      The Equation from Wiki, and others webs, seems these:

      From Wikipedia

      The Steinhart–Hart equation is a model of the resistance of a semiconductor at different temperatures. The equation is:
      

      Steinhart-Hart Equation.png

      T is the temperature (in kelvins),
      R is the resistance at T (in ohms),
      A, B, and C are the Steinhart–Hart coefficients, which vary depending on the type and model of thermistor and the temperature range of interest
      

      Dude 1: What are the values of R (the resistance in ohms), R(in middle) is the resistance of thermistor when temperature its B? and R(in final) is the resistance of thermistor when temperature its C?

      Dude 2: m305, can use C parameter ( the Steinhart-Hart C coefficient, default 0), but i can't see this variable in formula. Where its used?

      Thanks

      Danal 1 Reply Last reply Reply Quote 0
      • Danal
        Danal @peirof last edited by

        @peirof said in Dudes about Steinhart-Hart Equation:

        What are the values of R (the resistance in ohms), R(in middle) is the resistance of thermistor when temperature its B? and R(in final) is the resistance of thermistor when temperature its C?

        I am going to attempt to directly answer your questions; at the same time, the way you've phrased the questions indicates a basic misunderstanding of how equations work. I suggest you talk to a math teacher about the equation. That teacher does not have to know anything about thermistors or such. They just need to explain to you that "A" "B" and "C" only change when a different thermistor is used... therefore, the only two things that can change are T and R. Changing T changes R. And that's it.

        Get someone to discuss equations with you. Only then will any of this make any sense.

        In the above equation, "T" is the temperature; "R", resistance in ohms, will have the same value both of the places it occurs. "R" will only change when the temperature changes (or a different thermistor is used, which will have different "A", "B", and "C" coefficients)

        m305, can use C parameter ( the Steinhart-Hart C coefficient, default 0), but i can't see this variable in formula. Where its used?

        c7e7f8b2-ac51-49c9-9b20-aed181b3f42f-image.png

        Delta / Kossel printer fanatic

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        • nhof
          nhof last edited by

          What are you actually trying to do? Program a thermistor accurately into the duet or something else?

          If you are trying to get a thermistor model from measurements you have taken for T1/R1, T2,R2, and T3,R3, you can't use the equation as is. You should use a calculator like this one: https://www.thinksrs.com/downloads/programs/therm calc/ntccalibrator/ntccalculator.html. Put your temperatures in to get the A, B, C coefficients which you can then plug into the formula you posted.

          Formula is used when you already know the A,B, C coefficients and resistance R to calculate the temperature T. For most therms R and T have an inverse relationship (Most therms are NTC which means negative temperature coefficient).

          You might also use the words "Question" and "Questions" instead of "Dude" and "Dudes". "Question" is the correct word, it will make it easier for others to understand 🙂

          1 Reply Last reply Reply Quote 1
          • peirof
            peirof last edited by

            Hi,

            The idea its draw in Excel ot similar the Stein hart función.... For what:

            • i have used the web, but after put the temperature /resistance pair and obtain a B for put in Duet. When Duet hoy the nozzle, the temperature measured its 20 degrees, aprox, far of the Duet showed temp....
            • i d like see the effect of change B, in the curve. Maybe, of o can see the responde graph change, with a rapid feedback... Can fine tuning B value.
            • For adjust the M305, in this momentos, i do triying. Change B value, heat nozzle to working temperature, and see how near or far its from Real temperature
            • know my math skills are límited, like English... and I apologize for it

            Thanks for help

            Danal 1 Reply Last reply Reply Quote 0
            • Danal
              Danal @peirof last edited by

              @peirof said in Dudes about Steinhart-Hart Equation:

              i d like see the effect of change B, in the curve

              https://www.thinksrs.com/downloads/programs/therm calc/ntccalibrator/ntccalculator.html

              Delta / Kossel printer fanatic

              1 Reply Last reply Reply Quote 0
              • peirof
                peirof last edited by

                R in general formula, its the resistance at ambient temperature... Not its the same R of coeficients... No?

                1 Reply Last reply Reply Quote 0
                • nophead
                  nophead last edited by

                  R in the equation is the resistance of the thermistor at temperature T, they are the variables. A, B, C are constants for a given thermistor.

                  When T is 25C then R will be the thermistor's nominal resistance, e.g. 100K.

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                  • dc42
                    dc42 administrators last edited by

                    The B value entered in M305 or M308 is the reciprocal of the B coefficient in the S-H equation. This is because when C is zero, it's the Beta value in the thermistor beta model.

                    Duet WiFi hardware designer and firmware engineer
                    Please do not ask me for Duet support via PM or email, use the forum
                    http://www.escher3d.com, https://miscsolutions.wordpress.com

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                    • peirof
                      peirof last edited by

                      Hi,

                      after some reading, i think have a method for obtain Beta, for unknow termistors.

                      i have do a spreadsheet with the system...

                      I have do some test, and seems works.

                      Still to be done

                      • Draw the graph
                      • Calculate the value of C, for M305

                      Could someone please review it, to tell me what mistakes it has?

                      Calculate Beta for the thermistor.xls

                      Thank you

                      1 Reply Last reply Reply Quote 0
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