Thermal Coefficient of Resistance (TCR)

Thermal coefficient of resistance (TCR) is the calculation of a relative change of resistance per degree of temperature change. It is measured in ppm/°C (1 ppm = 0.0001%) and is defined as: TCR = (R2– R1)/ R1 (T2– T1). For high-precision resistors, this specification is typically expressed in parts per million (ppm) per degrees Celsius, with reference to normal room temperature, typically +25°C.

Despite the importance of this specification, individual resistor manufacturers use different methods for defining TCR on their published datasheets. In most cases, this definition does not provide enough information to enable an end user to accurately predict the influence of temperature changes on the resistance value. Where such published TCR variances are of concern, of course, is in their potential to create measurement uncertainty. Particularly, in applications where high-precision resistor performance and temperature stability are absolute requirements. This uncertainty is created when there is insufficient confidence that a TCR specification has been calculated with enough data to allow for the accurate prediction of the true impact of temperature change on resistor performance.

For example, some manufacturers may opt to list TCR as ±5 ppm/°C or ±10 ppm/°C, without reference to temperature range. Others may specify TCR as ±5 ppm/°C from +25°C to +125°C, yet omit data regarding other temperature ranges. In high-precision devices, published TCR specifications include nominal typical curves, normally from –55°C to +125°C. Those curves define nominal “cold” (–55°C to +25°C) and “hot” (+25°C to +125°C) chord slopes.