The reason why the temperature coefficient of resistance is expressed in positive and negative

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The reason why the temperature coefficient of resistance is expressed in positive and negative [Copy link]

Most chip resistors are specified with positive and negative values, such as ±100ppm/℃ or ±200ppm/℃.

This means that the resistance value may change in either direction due to temperature changes.

The following uses thick film chip resistors as an example to explain the reason.

When the temperature characteristics of the thick film chip resistor do not change linearly, when the horizontal axis is temperature and the vertical axis is resistance, it will present the change curve shown in the figure below.

This varying behavior is caused by the temperature characteristics of the materials used in thick film chip resistors.

Typical thick film chip resistor resistance change behavior

The intersection of the horizontal axis and the vertical axis in the above figure is the reference temperature, which represents the normal temperature of 25℃ (or 20℃).

In the above figure, for the blue line, since the positive and negative slopes alternate with the reference temperature as the center, in the area below the reference temperature, it shows a negative slope that the resistance value decreases with increasing temperature, and in the area above the reference temperature, it shows a positive slope that the resistance value increases with increasing temperature.

However, the vertex of the curve of the relationship between temperature and resistance value of actual resistor materials may be different.

The following explanation is given by taking ① to ③ in the following figure as an example.

① to ③ in the figure below are temperature and resistance curves for the same material. Since the material is manufactured in different batches, the temperature coefficient of resistance is different, so the positions of the vertices in the graph are also different.

This ultimately results in differences in the TCR of different product batches, and even when the resistors are used within the same temperature range, the positive and negative behavior of the resistance value change has a temperature range that varies from product to product.

[Example]

Compare the cases where the vertices in the graph are ①80℃, ②±0℃, and ③+100℃

→For ① to ③, what kind of resistance value change behavior will be shown at 80℃ to ±0℃ and ±0℃ to +100℃?

Batch Differences in Resistance Value Change Behavior

It can be seen that even within the same product and the same temperature range, different products will have different resistance change behaviors. Therefore, in order to indicate that the resistance value may change in both positive and negative directions, the value of the temperature coefficient of resistance is specified as positive or negative.

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