![]() By generating data from the two equations, then curvefitting it, we can produce a simple fit as shown in the following graph. An even better way of doing the computation arises from recognizing that the curvature inherent in the R TH vs Counts equation counter-balances the curvature of the T vs R TH equation, suggesting that a nearly linear approximation or a simple polynomial may work better than using the two equations in tandem. See how-do-rtds-work for a discussion of the temperature coefficient of resistance of RTDs. Typical resistivities can be found in the Useful Tables part of the Knowledge Base. RTDs are characterized by their temperature coefficient,, defined as the average fractional change in resistance per degree Centigrade over a temperature interval of 0☌ to 100☌. The standard has tables of maximum allowable resistance for various copper and aluminium cables. To improve efficiency you could use a lookup table or piecewise linear approximations. Z-255 ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms ☌ Ohms-100 59.57 -38 84.80 24 109.51 86 133.75 148 157.53 210 180.86 272 203. resistance is given by IEC 60228 'Conductor of insulated cables'. These calculations are involved, using many multiplies, divides, and a logarithm, which itself may involve a dozen operations. The current git version of the UliEngineering library implements this algorithm by using precomputed polynomials that are automatically selected if you pass R0100.0 or R01000.0 to ptxtemperature(), which is internally called from pt100temperature() and pt1000temperature(). The straight-forward way is to first calculate the thermistor resistance from the A/D counts using the equations shown on the page Measuring Thermistors, then to calculate the temperature in ☌ using the fancy polynomial equation with the logarithms shown on the page Temperature Resistance Equation. This particular thermistor has a calibration point resistance of R o = 2252 Ω at T o = 25☌.Ĭomputing the temperature can be done in a straight-forward but computationally inefficient way, or the calculation can be optimized. In this example we'll show how to use the Yellow Springs Type YSI 400 NTC thermistor 1), and compute the temperature directly from A/D counts with moderate accuracy. You can most efficiently compute temperature directly from A/D counts.
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