Measuring shunt – how does it work and where is it used?

Measuring shunt is one of the most important elements used in electrical engineering and power electronics for current measurement. Thanks to its simplicity, reliability, and high accuracy, it is used in many circuits where it is necessary to measure large currents safely and consistently.

Understanding what a shunt is, how it works, and where it is applied is crucial for those involved in the design, maintenance, or diagnostics of electrical installations.

Shunt – definition and principle of operation

A shunt is a special measuring resistor with very low resistance (usually fractions of an ohm), which is connected in series in the circuit where the measured current flows.

Its operating principle is based on Ohm’s law – the flow of current causes a voltage drop across the shunt, proportional to the current value. In practice, this voltage is very small, e.g., 75 mV at the full current range. This is why terms such as measuring shunt 50A 75mV or current shunts with higher ranges, e.g., hundreds or thousands of amperes, are popular.

This small voltage drop can then be measured using a voltmeter or a properly calibrated ammeter. As a result, the instrument indicates the value of the current flowing in the circuit.

Shunt and current measurement

The primary application of a shunt is current measurement. In practice, several key advantages can be distinguished:

• the ability to measure high currents, reaching tens of thousands of amperes,
• accurate readings in both dc (direct current) and ac (alternating current) circuits,
• simple design and high measurement accuracy,
• safe operation thanks to the isolation of the measuring part from high current values.

In many cases, a measuring shunt is used together with an ammeter, where the value is read based on the voltage generated by the shunt resistor.

Shunt and ammeter – how does it work?

An ammeter is an instrument that by itself cannot measure high currents because it requires a limited range. To properly connect an ammeter to the circuit, a shunt is used.

The shunt ensures that only a small part of the current flows through the measuring instrument, while the main flow passes through the shunt resistor. Thanks to this, even high current values, e.g., 50A 75mV, can be recorded by classic analog meters or modern digital instruments.

In practice, it is said that a shunt “extends the measurement range of an ammeter.”

Shunt and voltmeter

Although most often associated with an ammeter, a shunt can also work with a voltmeter. Since the voltage across the shunt is proportional to the flowing current, it is enough to calibrate the voltmeter so that its readings correspond to the current in the circuit. This makes it possible to easily create a reliable measuring system.

Typical parameters of a shunt

A shunt is mainly characterized by two parameters:

1. Current range – the maximum current that can flow through it without the risk of damage or overheating. This can be small values (a few amperes) or very large ones (thousands of amperes).

2. Voltage drop – typically 75 mV at maximum current, although other values are also available.

An example is a measuring shunt 50A 75mV, which means that when 50 amperes flow through the shunt resistor, a voltage drop of 75 millivolts occurs.

Applications of a measuring shunt

Current measurement in electrical installations

A shunt is commonly used in both direct current and alternating current circuits where it is necessary to measure the current flowing through heavily loaded conductors. It is found, for example, in distribution systems, industrial batteries, and power installations.

Electronics and automation

In electronic devices and automation systems, a shunt functions as a measuring element in control and protection circuits. Thanks to it, it is possible, for example, to record current over time as well as to control the operation of devices based on measurement data.

Industry and energy

In industrial plants, current shunts are used to monitor high currents in technological processes, e.g., in welding machines, electrolysis, or power supply systems. Their high resistance to working conditions and accuracy make them an essential component in many industries.

Laboratories and metrology

In measurement laboratories, shunts are used for calibration of measuring instruments and for conducting precise research. Measurement accuracy and stability of shunt parameters are crucial here.

Analog and digital shunt

In classic systems, analog shunts are used, which work with traditional analog meters. Modern solutions increasingly use digital shunts, which integrate current measurement with signal processing and can be connected directly to monitoring systems.

Selecting and using a shunt

When choosing a shunt, attention should be paid to:

• the resistance value of the shunt,
• the maximum operating current,
• the required voltage drop (usually 75 mV),
• working conditions (temperature, environment, possibility of short circuits),
• measurement accuracy required in a given application.

Proper connection of the shunt and selection of wires are of great importance for obtaining accurate readings.

Advantages of using shunts

• the ability to measure high currents without the risk of damaging the measuring instrument,
• high measurement accuracy,
• simple design and safe and reliable operation,
• a wide range of available models – from a few amperes to thousands of amperes,
• compatibility with both analog and digital meters.

Summary

A measuring shunt is a simple component but of great importance for current measurements. By using a shunt resistor with low resistance, it is possible to accurately and safely measure high currents in both ac and dc circuits.

Used in ammeters, voltmeters, or modern digital systems, the shunt remains indispensable wherever precision and reliability are required. From metrology laboratories, through industry, to power engineering – its role is invaluable.

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