/// <summary>
/// The Beta model is a simple but not-so-accurate way of calculating a temperature from a thermistor's resistance.
/// Steinhart-Hart is better, but Beta will have to do if we only know the Beta parameters for our thermistor.
/// </summary>
/// <param name="betaModelParameters"></param>
/// <param name="resistanceOhms"></param>
/// <returns></returns>
public double ConvertResistanceToTemperatureCelciusUsingBetaModel(ThermistorBetaModelParameters betaModelParameters, double resistanceOhms)
{
// T = [(1 / β) ln(RT / RT0) + 1 / T0 ] ^ - 1
// From: https://www.thermistor.com/sites/default/files/specsheets/Beta-vs-Steinhart-Hart-Equations.pdf
var celciusToKelvin = 273.15;
var oneOverBeta = 1/betaModelParameters.BetaValue;
var logResistanceOverReferenceResistance = Math.Log(resistanceOhms/betaModelParameters.ReferenceResistanceAt25DegC);
var oneOverReferenceTemp = 1/(25 + celciusToKelvin);
var resultKelvin = Math.Pow((oneOverBeta * logResistanceOverReferenceResistance) + oneOverReferenceTemp, -1);
var resultCelcius = resultKelvin - celciusToKelvin;
return resultCelcius;
}
/// <summary>
/// The Beta model is a simple but not-so-accurate way of calculating a temperature from a thermistor's resistance.
/// Steinhart-Hart is better, but Beta will have to do if we only know the Beta parameters for our thermistor.
/// </summary>
/// <param name="betaModelParameters"></param>
/// <param name="resistanceOhms"></param>
/// <returns></returns>
public double ConvertResistanceToTemperatureCelciusUsingBetaModel(ThermistorBetaModelParameters betaModelParameters, double resistanceOhms)
{
// T = [(1 / β) ln(RT / RT0) + 1 / T0 ] ^ - 1
// From: https://www.thermistor.com/sites/default/files/specsheets/Beta-vs-Steinhart-Hart-Equations.pdf
var celciusToKelvin = 273.15;
var oneOverBeta = 1 / betaModelParameters.BetaValue;
var logResistanceOverReferenceResistance = Math.Log(resistanceOhms / betaModelParameters.ReferenceResistanceAt25DegC);
var oneOverReferenceTemp = 1 / (25 + celciusToKelvin);
var resultKelvin = Math.Pow((oneOverBeta * logResistanceOverReferenceResistance) + oneOverReferenceTemp, -1);
var resultCelcius = resultKelvin - celciusToKelvin;
return(resultCelcius);
}
public void GivenBetaModelParameters_WhenIHaveAResistance_ThenICanCalculateTemperature()
{
// Arrange
// Values for my thermistor, from http://www.surplustronics.co.nz/products/2140-ntc-thermistor-10k-ohms
var betaModelParameters = new ThermistorBetaModelParameters
{
BetaValue = 4100,
ReferenceResistanceAt25DegC = 10000
};
// Act/Assert
_thermistorCalculator.ConvertResistanceToTemperatureCelciusUsingBetaModel(
betaModelParameters,
10000).Should().BeApproximately(25, 0.01, "because that's the reference temperature");
_thermistorCalculator.ConvertResistanceToTemperatureCelciusUsingBetaModel(
betaModelParameters,
1000).Should().BeApproximately(84.96, 0.01, "because that's the the value I get from the online calculator at http://www.thinksrs.com/downloads/programs/Therm%20Calc/NTCCalibrator/NTCcalculator.htm");
_thermistorCalculator.ConvertResistanceToTemperatureCelciusUsingBetaModel(
betaModelParameters,
28000).Should().BeApproximately(4.23, 0.01, "because that's the the value I get from the online calculator at http://www.thinksrs.com/downloads/programs/Therm%20Calc/NTCCalibrator/NTCcalculator.htm");
}
