Resistor TCR depends on the purity and temperature of the resistor material

The exact value of the resistor stability factor depends on the purity and temperature of the resistor material. The temperature coefficient of resistance, TCR, is one of the main parameters that characterize resistance. TCR defines the change in resistance as a function of ambient temperature. A common way to express TCR is in ppm/°C, which stands for parts per million per degree Celsius. We generally calculate the temperature coefficient of resistance through some formulas. At present, many low temperature drift resistors have very low TCR, and these resistors are mainly used in high-end instrumentation.

The TCR of a resistor is negative, positive, or stable over a certain temperature range. Temperature compensation can be avoided by choosing the right resistor. In some applications, a large TCR is required, for example to measure temperature. Resistors used in these applications are called thermistors and can have a positive (PTC) or negative temperature coefficient (NTC).

How to measure TCR

The temperature coefficient of resistance of a resistor is determined by measuring the resistance value over an appropriate temperature range. TCR is calculated as the average slope of resistance values within this interval. This is exact for a linear relationship because the TCR is constant at any temperature. However, many materials have nonlinear coefficients. In the case of nickel-chromium, a popular resistance alloy, the relationship between temperature and TCR is not linear.

Since the resistor TCR is calculated with the average slope, it is very important to determine the resistor TCR and temperature interval. The measurement method of resistor TCR can be consulted in some resistance test contents. Use this method to calculate TCR in the range of -55 to 25°C and 25 to 125°C. Since the highest measured value is defined as TCR, this approach often results in specifying an excessively high resistance in less demanding applications.