Dudes about Steinhart-Hart Equation

peirof

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

@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?

nhof

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

peirof

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

@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

peirof

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

nophead

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.

dc42

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.

peirof

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