steinhart hart equation

[vijay shankar]

Hi, 

I am using a 30 K Ohm @25 C thermistor to get and set temperature at a peltier device being controlled by the controller.

To convert the readings from the device to C reading and to convert the value to be set into thermistor values from C value, I need to write a subvi to implement the same.

I dont have any document provided by the thermistor vendor. To implement the Steinhart-Hart equation, I need to know the "A, B & C" values. I tried to find it out, but never got a clue. The Convert Thermistor Reading.vi given in the labview is confusing, as I dont know how to caliberate it for 30 K Ohm @ 25 C thermistor.

Can anyone help me out.

Thanks,

Vijay 

[Pnt]

You don't need anything. Just some measurments.

You have one : 30K OHm @ 25C

You need at least two more. Measure the resistance in, lets say 40C and at 0C.

The more measurments you make and at a wider range, the more acurate the equation will be.

Then i usually put the data to Excel and it gives me the equation.

There is a vi in Labview that does the same but i don't remember where it is

[jpaul]

Hi Vijay,

If you double-click the Convert Thermistor Reading VI to bring up its front panel there is detailed comments on how to approriately configure it for your case. It appears for your case you would wire 30k to R1 and then if it is Voltage Excitation wire in your voltage reference. Finally wire your data to Voltage input. Hopefully this points you in the right direction, but let me know if you have any further questions/concerns.

Cheers,

[vijay shankar]

Hi,

I will be getting a value in ohms from a thermistor which is a 30k ohm @ 25 C thermistor.

I have a table that maps a given integer temperature to a ohm value like in the attachment I have attached with this post. 

But to set a temperature I can use a select case structure. But when I read the temperature, I should convert the ohm value to the temperature which is difficult.

To calculate the temperature from a given R value, I have to use Steinhart-Hart equation for which I dont know the A, B and C (co efficient) values which holds true for the 30 K Ohm thermistor I have.

The vi given in labview says, its for 5k ohm thermistor. How do I accomplish this?

Thanks,

Vijay 

[DSPGuy]

Vijay,

It looks like you have a nice table of values from the manufacturer, so you could use the interpolation VIs (Interpolate 1D.vi) to deal with this.  Duplicate the table as two 1-D arrays.  The R values (array) will be the X input to the interpolation VI, and the Temp values (array) will be the Y values.  The xi input will be all the R values for which you want the Temperature.

You could also treat this as a fitting problem, where your model is the Steinhart-Hart equation, and the data is the same table used for the interpolation outlined above.  Once you solve for the model parameters, you could then evaluate the model at a given R value and recover the Temperature.

-Jim

[rhino13]

i am verifying an answer to problem: What is temperature using Steinhart equation id R is 15,500 Olms a =0.23641133E-4, b=0.110123770 and c=0.148090329