What are the applications of resistors and shunts in current measurement?

　　The shunt is a resistor in principle. The definition of shunt in "GB/T 2900.79-2008 Electrical Engineering Terminology" is that the shunt is a resistor connected in parallel with the current circuit of the measuring instrument to expand its measurement range. However, in actual current measurement, there is a big difference between shunt and resistor.

1. What are the applications of resistors and shunts in current measurement?

　　Traditionally, resistors that measure small and medium currents are called resistors, and resistors that measure large currents are called shunts. Resistors and shunts are the most widely used current measurement methods. Current is passed through a resistor and the voltage drop across the resistor is measured. It directly applies Ohm's law to convert current signals into voltage signals. This method is simple to use, easy to operate, and low cost.

　　The accuracy of this measurement method depends on the accuracy, temperature coefficient, and time stability of the resistor. Due to the characteristics of the resistor material, the resistance value of the resistor is not constant, but changes with temperature, frequency, time, etc. For example, the temperature coefficient of an ordinary resistor is about 100ppm/℃, and a temperature change of 10℃ can cause a change of about 1‰ in resistance, which is an important source of error. On the other hand, the resistor will also change over time, and this change is random. The annual change rate (aging rate) of ordinary resistors is also on the order of 1‰/year.

　　High-precision measurement systems require high-precision resistors or shunts with low temperature coefficients and high time stability (annual aging rate). The temperature coefficient of copper materials is about 4‰/℃, and low temperature coefficient manganese copper and constantan materials can generally achieve 10~50ppm/℃. Better resistor materials from Germany's Isabellenhuette or the United States' Vishay can achieve ppm/℃ or even less than 1ppm/℃. The standard resistor used for measurement is less than 0.1ppm/℃.

　　The resistor or shunt needs to be directly connected in series with the current loop, and can only be measured in a non-isolated form (excluding the isolation of the subsequent circuit). Generally, there is no problem because the subsequent handheld or desktop multimeters are isolated.

　　Main application areas: low voltage (no isolation required), medium and low current occasions.

　　It is generally suitable for current measurement of 10A and below. The heating of the shunt above 10A will affect the performance. The maximum measurement capacity of the shunt is about 1kA.

2. What are the advantages and disadvantages of resistor and shunt measurement?

　　Advantages: easy to understand principle, simple structure, easy to implement, low cost, high bandwidth

　　Disadvantages: The measured current loop and the measuring loop are not electrically isolated, and they interfere with each other, especially in high voltage situations, which can easily damage the measuring loop; the shunt resistor will lose power and generate heat, which is especially serious in high current situations. The value of the resistor will change with temperature, affecting the measurement accuracy; the shunt heating may require cooling measures such as air cooling and water cooling, which are large and inconvenient to use; high-performance shunts (high precision, low temperature coefficient) are expensive; the voltage drop on the resistor is generally small, and it needs to be further amplified before it is easy to use. The zero position, gain, and temperature characteristics of the amplifier circuit all affect the final accuracy; large current measurement requires extremely small resistors, and the accuracy itself is difficult to achieve.