If the temperature starts to change, the resistance value for all kinds of resistors also has an adjustment. Based on the fact that the value of R returns to normal when the temperature is normal, this informative article focuses only on temporary adjustments that occur when the temperature changes. Temperature has two implications for the resistance level. As a result, the actual size of the resistant material changes and the cross-sectional area increases as well as the length. Another effect is a change in the resistance value of the material and all the materials that we use to make resistors, the change in resistivity is much greater than the change as a result of changing proportions that we can focus on this change alone.
The property of materials that is used to study the effects of temperature changes is known as the temperature coefficient, and strictly speaking, the coefficient we use is the temperature coefficient of resistance or TCR. Definition is a fractional difference in the degree of resistance per degree Celsius. A positive result is observed at TCR, when an increase in temperature leads to an increase in resistance, and a negative result depends on the TCR, when the temperature decreases. Although in most cases a low temperature coefficient is needed to maintain relatively stable resistance values. Many resistors are specifically designed to provide a higher temperature coefficient for the resistor. These types of resistors are known as thermistors and can be useful for measuring temperature or overcurrent protection. For these thermistors, semiconductor metal oxides are commonly used. However, there are also silicon-based thermistors, they show a more linear response.
As a rule, good conductors, such as metals, always have a positive temperature coefficient (PTC), but semiconductor materials usually have a negative coefficient, and carbon resistors can also have NTC. In addition, there are thermistors with a very high TCR (positive or negative). To show temperature coefficients so that they are easily accessible or unforgettable, the temperature coefficient is often indicated in parts per million per degree. For example, we write the value as 250 ppm / ° C, rather than 0.00025 / ° C, when we talk about a resistor relative to the temperature coefficient of the resistor, because it is a more compact form that can be easily remembered using statistics.
