Convert resistance to temperature for Pt100 or Pt1000 RTDs, NTC thermistors and copper or other conductors, or calculate resistance from temperature.
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Resistance to Temperature Formula
The following constant-coefficient approximation calculates a temperature change from resistance. It is a linear conductor model over an appropriate interval, not the full platinum RTD or NTC relationship.
- Where ΔT is the change in temperature
- R(T2) is the resistance at temperature 2
- R(T1) is the resistance at temperature 1
- a is the temperature coefficient per °C (equivalently per K), referenced to T1.
To calculate the temperature change in the linear model, divide R(T2) by R(T1), subtract 1 and divide by the coefficient referenced to T1. Then T2 = T1 + ΔT. A change in kelvins equals a change in degrees Celsius, but absolute temperatures use different offsets.
| ΔT (°C) | Resistance at T2 (Ω) |
|---|---|
| -50 | 80.750 |
| -40 | 84.600 |
| -30 | 88.450 |
| -20 | 92.300 |
| -10 | 96.150 |
| -5 | 98.075 |
| 0 | 100.000 |
| 5 | 101.925 |
| 10 | 103.850 |
| 20 | 107.700 |
| 25 | 109.625 |
| 30 | 111.550 |
| 40 | 115.400 |
| 50 | 119.250 |
| 60 | 123.100 |
| 80 | 130.800 |
| 100 | 138.500 |
| 150 | 157.750 |
| 200 | 177.000 |
| 300 | 215.500 |
| Uses R2 = R1 × (1 + α × ΔT), with R1 = 100 Ω and α = 0.00385/°C. This is an illustrative linear table, not an IEC platinum calibration table. Use the RTD modes for the nonlinear platinum model. | |
How are resistance and temperature related?
For many metals, resistance rises as temperature rises; NTC thermistor resistance falls instead. Resistance alone does not determine a component’s self-generated temperature. Heating also depends on electrical power and heat transfer. Use a sensor’s specified resistance–temperature model to infer temperature from a reading.
How to Calculate Resistance to Temperature?
Example Problem:
The following example outlines the steps and information needed to calculate temperature from resistance.
First, determine the resistance at temperature 2. In this case, the resistance at T2 is measured to be 50 ohms.
Next, determine the reference resistance and temperature. For this illustration, R(T1) = 20 ohms at T1 = 20°C.
Assume a linear coefficient of 0.25 per °C at the reference temperature for this arithmetic example. This is a hypothetical coefficient, not a typical platinum RTD or thermistor value.
Finally, calculate the change in temperature using the formula above:
ΔT = (R(T2)/R(T1)-1)/a
ΔT = (50/20-1)/.25
ΔT = 6°C, so T2 = 20°C + 6°C = 26°C.
The RTD modes use the platinum Callendar–Van Dusen relationship (A = 3.9083 × 10⁻³, B = −5.775 × 10⁻⁷, C = −4.183 × 10⁻¹²), with the negative-temperature branch below 0°C and a modeled interval of −200°C to 850°C. A particular probe may have a narrower rating. The NTC modes use R = R25 × exp[β(1/TK − 1/298.15)], with absolute temperature in kelvins and a datasheet beta interval. Lead correction subtracts only an entered total contribution; tolerance, calibration and self-heating are excluded. See TI platinum RTD model guidance and TI NTC beta-model guidance.
