Steinhart-Hart equation1/T = A + B * ln(R) + C * (ln(R))3
- T is the temperature (in Kelvin)
- 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. (The most general form of the applied equation contains a [ln(R)]2 term, but this is frequently neglected because it is typically much smaller than the other coefficients, and is therefore not shown above.)
20K NTCTemperature | Resistance |
-40 F | 830741 |
0 F | 195197 |
70 F | 24037 |
100 F | 11241 |
150 F | 3665 |
200 F | 1391 |
20K NTC fed from 10 uA source
20K NTC with output across load resistor
Resources
Microchip AN685 Thermistors in Single Supply Temperature Sensing Circuits
Wikipedia - Steinhart-Hart equation
Stack Exchange - How to measure temperature using a NTC thermistor?
Daycounter, Inc. - Steinhart-Hart Thermistor Calculator
Sourceforge.net - support for NTC thermistor calculations