How to measure Temperature Coefficient of Resistance (TCR)?

How to measure Temperature Coefficient of Resistance (TCR)?

The Temperature Coefficient of Resistance, or TCR, is a measurement of a resistor's change in resistance per change in temperature. It is typically measured in ppm/°C, that is, parts-per-million change in ohms per change of 1 degree centigrade. Common values might be 5 or 10 ppm/°C, while precision resistors might have values of <0.1ppm/°C. Because it a measure of change per external factor, TCR is a measurement of resistance linearity.

This measurement is typically done in a calibration lab with a precision temperature chamber and a DMM. For the resistance measurement, the important specification is NOT the overall accuracy of the instrument, somewhat confusingly. Instead, the important specification is ADC linearity. This is because the measurement is most interested in determining the change of a value rather than measuring the value exactly.

Linearity is an uncommon spec and is often only given in the full specifications document of a DMM. It is commonly given in ppm of range, or sometimes in % of range. Generally a single ADC will have the same linearity on every range, but check your instrument for specifics.

For TCR, you want your DMM's linearity to be more precise than the TCR you're attempting to measure. For example, the Keithley 2002 8.5 Digit Multimeter has a specified ADC linearity of <0.1ppm of range typical, <0.2ppm maximum. This meter could reliably measure TCR of >0.2ppm/°C, assuming the paired temperature chamber has an acceptable accuracy.