The resistor changes its value when the temperature changes. This is the reason why circuits that contain these elements must work in environments where the temperature is normal and constant.
If this is not the case, and the temperature at the place where the element is located changes to a known value, then you can get the new resistor's value using the following formula:
Rtf = Rto x [1 + a (tf - to)]
Where:
- Rtf = final resistor value at a temperature tf in ohms
- Rto = initial resistor value at a temperature to, in ohms
- α = temperature coefficient (see table below)
- tf = final temperature in °C
- to = initial temperature in °C
Table of coefficients of resistor variation per degree temperature.
For Example:
If we have a copper conductor with a resistance = 20 ohms at 10°C., what will the new resistor value be, if the temperature rises to 70°C.?
Using the formula:
Rtf= Rto x [1 + a (tf - to)]
and using the following values:
- Rto = 20 ohms
- α = 0.00382 (copper)
- tf = 70 °C
- to = 10 °C
We get:
Rtf = 20 [1 + 0.00382 (70 - 10)] = 24,584 ohms
