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The Measurement Accuracy of Automotive Shunt is Affected by Resistivity and TCR

Writer:Microhm Page View:Date:2019-03-06
Generally, Mn-Cu alloy is used for production of automotive shunt. Mn-Cu alloy has relatively small temperature coefficient of resistance (TCR), low thermal EMF against copper, excellent annual stability of resistance, good weldability and workability. We know that the resistance value will change with temperature. For automotive shunt, the change of resistance value directly affects the precision of measurement. For precision instrument, this effect is enough to constitute an error to the precision.
The resistivity and stability coefficient of automotive shunt are very important to it. In many high-precision measurement fields, the temperature rise of the shunt has become an important factor affecting the measurement accuracy of the shunt. So what is the relationship between the influence of automotive shunt and its temperature coefficient of resistance and resistivity? let's analyze it as follows:
First, we analyze the resistance temperature coefficient of automotive used shunt. The resistance temperature coefficient indicates the relative change of resistance value when the temperature changes 1 degree. It refers to the ratio of the added value of the conductor resistance to the original resistance at 1 ℃ temperature increasement. The unit is ppm/ ℃. The smaller the temperature coefficient of resistance is, the smaller the change of temperature rise to resistance value. For the current sampling shunt, the smaller the resistance temperature coefficient, the less the influence on the measurement. In order to reduce the resistance temperature coefficient, the shunt is usually made of alloy material, such as MnCu alloy.
Secondly, the resistivity change of automotive shunt is used to represent the physical quantity of resistance characteristics of a variety of materials. The ratio of the product and length of the resistance to the cross-sectional area of the original made of a substance (20 °C at room temperature) is called the resistivity of the substance. The resistivity is independent of the length and cross-sectional area of the conductor, and is the electrical property of the conductor itself, which is determined by the material of the conductor and depends on the temperature. Unit of resistivity is ρ. In the international unit system, the unit of resistivity is ohmmeter (Ω ·m).

It can be seen from the above two points that with the increase of the current, the temperature rise has a greater effect on the measurement of the automobile shunt. In the case of small current, this effect can be completely ignored, but the larger the current, the greater the error will be, which becomes an important influence factor. When we use the automotive shunt, we attach great importance to his resistivity and temperature coefficient of resistance, especially in the automotive battery management system, which has a great impact on the whole automotive battery management system.

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