Shunt (electrical)

A shunt is a low impedance electrical resistor, which is used for measuring the electric current ( sense resistor ). The current flowing through a shunt, causing a voltage drop proportional to it, which is measured.

Principle

Electricity meters with analog or digital gauges are usually implemented via a measurement of very small voltage across a shunt, eg 200 mV with digital instruments or customary 60 mV at hand instruments. Electronic circuits with operational amplifiers can also handle lower voltages across the shunt. The lower the voltage, the less influence the measurement of the circuit.

The shunt is installed to the line with the current to be measured. The falling small voltage across this resistor is measured by the meter. As a significant voltage drop caused by the contact resistance at the current contacts, the measured voltage drop across the shunt with two additional contacts ( four-wire connection, even Kelvin connections or Kelvin - called contact ) tapped.

The current flowing through the shunt current is calculated according to Ohm's law: The voltage drop across a 200 milliohms shunt 200 mV, a current of 1 A. If the current flowing through the voltage meter flows is not negligibly small, it must it is included in the calculation.

Method of construction

To measure high (> 100 A) currents are shunt rugged mechanical construction, such as metal strips or rods with strong screw contacts for the measuring circuit and two smaller connections for the meter. Large shunts of parallel metal rods can be screwed directly between power rails. Materials for the resistors of manganin, constantan, Isotan, Isabellin. The aim is the lowest possible temperature coefficient of electrical resistance.

Furthermore, small shunts are made ​​for soldering printed circuits; these have often Kelvin contacts. The current is measured with a shunt has declined with the advent of current sensors ( they also have a potential separation) somewhat, but shunts are an inexpensive and accurate method of measuring current and are used not only in measuring devices in power electronics modules for power monitoring and control.

Low-inductive types

If you want to measure currents with short rise times and high frequencies, one must use special designs with low parasitic inductance. Axial or worse axially -wound resistors are then not applicable. More suitable are bifilar -wound resistors or special shapes, such as the coaxial shunt, consisting of two nested tubes, which are flowed through in the opposite direction of the current. More low-inductive types are the Möbius resistor or wavy resistance films.