8 replies to this topic

[PawleysPlayr]

I have a TTC 103 thermistor
The specs:

TTC Series

R₂₅ = 10000 ohms
B_25/50 = 4050
Disipation = 4.5mW/degC
Tolerance of R₂₅ = 5-10-15

Can someone show me how to get the A/B/C constants needed for the Steinhart-Hart Thermistor formula from the data sheet?

Or is there a better method using the thermistor?

[mpearson]

Hello PawleysPlayr,
I have some experience with thermistors, and know there is a way determine the coefficients, but am unsure of the way as I have not needed to.

This is a series from BC Components that is similar. They publish coefficients and therefore may be an alternative to speed up the process. This is what I have always used, and they work great.

Here is the datasheet

The coefficients for these would be:

A
0.003354016

B
0.0002519107

C
0.000003510939

D
0.0000001105179

I have applied this in the C language, so let me know if you have any other questions.

[PawleysPlayr]

Thanks! I guess you're right. I should pick up a thermister with the temp/R data on the datasheet. I would be interested in taking a look at you c solution. Just to verify what I've done.

[mpearson]

Below is how I applied it in C. If you have any questions, let me know!

//ADC_Value Accepted, Farenheit Returned
	double GetFarenheit(int ADC_Value)
	{
		//Define reference voltage
		double Vref = 5;

		//Define thremistor value
		double ThermRefResistance = 10000;
	
		//Convert ADC reading to a voltage
		double Vin = (Vref * ADC_Value) / 1024;
	
		//Convert Voltage to resistance
		double ThermResistance = ThermRefResistance/((Vref/Vin)-1);

		// Steinhart constants for thermistor (Vishay NTCLE203E3103FB0)
		double a = 3.354016 * pow(10, -3);
		double b = 2.56985 * pow(10, -4);
		double c = 2.620131 * pow(10, -6);
		double d = 6.383091 * pow(10, -8);

		//Convert resistance to temperature in degrees C (Steinhart equation)
		double Celcius = 1/(a + b * log(ThermResistance/ThermRefResistance) + c * pow(log(ThermResistance/ThermRefResistance), 2) + d * pow(log(ThermResistance/ThermRefResistance), 3)) - 272.15;
		
		//Convert celcius to farenheit

		return Farenheit = 18 * Celcius + 320;

	}

[mzwaterski]

Below is how I applied it in C. If you have any questions, let me know!

//ADC_Value Accepted, Farenheit Returned
	double GetFarenheit(int ADC_Value)
	{
		//Define reference voltage
		double Vref = 5;

		//Define thremistor value
		double ThermRefResistance = 10000;
	
		//Convert ADC reading to a voltage
		double Vin = (Vref * ADC_Value) / 1024;
	
		//Convert Voltage to resistance
		double ThermResistance = ThermRefResistance/((Vref/Vin)-1);

		// Steinhart constants for thermistor (Vishay NTCLE203E3103FB0)
		double a = 3.354016 * pow(10, -3);
		double b = 2.56985 * pow(10, -4);
		double c = 2.620131 * pow(10, -6);
		double d = 6.383091 * pow(10, -8);

		//Convert resistance to temperature in degrees C (Steinhart equation)
		double Celcius = 1/(a + b * log(ThermResistance/ThermRefResistance) + c * pow(log(ThermResistance/ThermRefResistance), 2) + d * pow(log(ThermResistance/ThermRefResistance), 3)) - 272.15;
		
		//Convert celcius to farenheit

		return Farenheit = 18 * Celcius + 320;

	}

Is it possible to use this code with the Netduino? When I try and use this, I'm told that the pow() and log() functions do not exist. Is there a package that I need to add to my environment?

[Dan Morphis]

Is it possible to use this code with the Netduino? When I try and use this, I'm told that the pow() and log() functions do not exist. Is there a package that I need to add to my environment?

Those are available in the Math library. Math.Pow(), Math.Log()

-dan

[mzwaterski]

Those are available in the Math library. Math.Pow(), Math.Log()

-dan

Thanks for your response. I tried this, and the Pow() function now works, but the Log() function is not working (e.g., System.Math.Log(ThermResistance / ThermRefResistance) reports that System.Math does not contain a definition for 'Log'). Do I need to somehow get a different Math library or version of something?

Thanks in advance for any help that you can provide.

Mike

[Valkyrie-MT]

...reports that System.Math does not contain a definition for 'Log'). Do I need to somehow get a different Math library or version of something?

Yeah, there are lots of little things missing and this is one of them. But, actually, there was some discussion about a Math.Log function previously. Link below. Just make sure you read to the end of the thread because the code does not work, but the fix is described. Sorry, I always meant to go back and post a corrected version of the log function...

http://forums.netdui...ndpost__p__6949

-Valkyrie-MT

[David E]

Hi , I put some posts here a couple of weeks ago (to which i received some replies)

they all seem to have been taken off the site.

Any ideas what happened? I was asking a question to Mike Pearson about the use of the particular Thermistor in the code below....

Below is how I applied it in C. If you have any questions, let me know!

//ADC_Value Accepted, Farenheit Returned
	double GetFarenheit(int ADC_Value)
	{
		//Define reference voltage
		double Vref = 5;

		//Define thremistor value
		double ThermRefResistance = 10000;
	
		//Convert ADC reading to a voltage
		double Vin = (Vref * ADC_Value) / 1024;
	
		//Convert Voltage to resistance
		double ThermResistance = ThermRefResistance/((Vref/Vin)-1);

		// Steinhart constants for thermistor (Vishay NTCLE203E3103FB0)
		double a = 3.354016 * pow(10, -3);
		double b = 2.56985 * pow(10, -4);
		double c = 2.620131 * pow(10, -6);
		double d = 6.383091 * pow(10, -8);

		//Convert resistance to temperature in degrees C (Steinhart equation)
		double Celcius = 1/(a + b * log(ThermResistance/ThermRefResistance) + c * pow(log(ThermResistance/ThermRefResistance), 2) + d * pow(log(ThermResistance/ThermRefResistance), 3)) - 272.15;
		
		//Convert celcius to farenheit

		return Farenheit = 18 * Celcius + 320;

	}