Briefly describe the importance of the operating temperature of shunt alloy resistors

Precision shunt alloy resistors have always been the shortcoming of my country's resistor industry. my country's current precision shunt alloy resistors are all imported to meet the needs. Its products have very high process requirements for alloy materials, and my country's existing alloy material processes still have a lot of improvement to do. Shenzhen Shida Electronic Technology Co., Ltd. has started the research and development of precision shunt alloy resistors with the help and support of international partners. At the request of the company, the R&D department will also make some brief introductions to the new products we are developing.

Ampere (A) is the basic unit of current in the International System of Units. The definition given by the International Weights and Measures Committee is: a constant current passes through two infinitely long parallel straight wires with negligible circular cross-sections 1 meter apart in a vacuum. When the force generated between the two wires per meter of length is equal to 2×10-7 Newtons, the current passing through the wire is specified to be one ampere. However, the two infinitely long wires in the definition cannot be realized. In actual operation, the current is calculated by measuring the voltage drop of the shunt and combining Ohm's law.

As shown in the figure below, the DC shunt is made of two copper joints and a resistor alloy in the middle. The four-terminal wiring method can accurately measure the current flowing through the shunt.

The shunt needs to work under a large current, and the surface temperature of the shunt will rise due to self-heating. Especially when the ambient temperature is high and the heat dissipation environment is poor, the surface temperature of the shunt will rise further. According to the IEEE standard, the recommended operating current of the shunt should not exceed 2/3 of the rated current under normal working conditions. However, in actual applications, it is often necessary to measure a larger range of currents, that is, we require the shunt to work normally at 10%-100% of the rated current, and sometimes even short-term overloads may occur. Regardless of the working conditions, it is very important to control the surface temperature of the shunt. Its working state is best at 30-70℃, and its surface temperature cannot exceed 145℃ under any circumstances, otherwise it will cause irreversible changes in the resistance value of the resistor alloy. It should be pointed out that the surface temperature of the shunt should be measured from the center point of the resistor alloy.
The need to measure a wider range of currents will result in huge differences in the heating conditions of the shunt. The resistance value of the resistor will change due to the self-heating caused by loading. The resistance value of the resistor will change differently when different currents are loaded.