A shunt resistor is a low ohm resistor that is used for current measurement
The bigger the current, that circulates through the shunt, the bigger the voltage, that can be measured.
Electricity measurement instruments with analog or digital gauges are commonly implemented by measuring the little voltage on a low ohmic shunt Such commonly is 200 mV in numeric measuring instruments, or 60 mV in ordinary analog instruments. Circuits with electronic amplifiers might also process smaller voltages on a shunt and therefore might also be adopted for high precision current sensing.
The shunt is incorporated in the circuit in which the current should be measured. The little voltage that occurs on the current resistor is measured with the displaying unit. For the reason that the resistance at the connection points bears the voltage to drop, the voltage on the power meter shunt is measured by a multy point connection (also called Kelvin connection).
The size of the shunt is chracterized by Ohm's law. For example: If the voltage drop on a 100 mOhm shunt is 100 mV, then 1 A of current circulates. If the current passing through the voltmeter is not very small, it has to be included in the size.
In order to determine large (> 100 A) flows shunts are mechanically strong, for instance as alloy band resistor made of Manganin with strong connection points for the measurement circuit and with two smaller connection points for the meter. Further Isotan, Constantan, Isabelline for current resistors are Isotan, Constantan, Isabelline.
Big shunts are made of a number of parallel alloy bars and can be incorporated directly between the power rails. A lot of times shunts are directly incorporated in the measuring instruments (eg multimeter) and are interchangeable.
For the measurement of enormous currents (> 50 kA), e.g. of lightning, commonly special built, commonly coaxial power resistor shunts are used. Those permit the measurement of current changes with storage scopes.
Yet, little shunts for mounting into electronic circuit boards are manufactured, which also have Kelvin connection points. Yet, shunts exist as electrical SMD Resistor or hybrid mounting resistors which commonly are incorporated in BMS Batterymanagement Systems.
The current measurement with high precision resistors like shunts decreased to some degree with the debut of current sensors (they also do a potential separation). Shunts still are an low-priced and precise means of current measurement.