How Ammeters Work

Electrical circuits and devices are complex systems, and their intricate and numerous components can make troubleshooting somewhat difficult. While one could test the overall functionality of a component through more manual means, tools such as ammeters are much more beneficial for troubleshooting a circuit with their ability to gather various readings. Ammeters are capable of measuring the amount of current present within a circuit, and they garner current readings in the form of amperes. As there are various types of ammeters available as well as similar devices such as galvanometers, it is important to understand the role of such instruments and how they differ from others.

Unlike measurements of voltage and resistance, measuring current requires the meter to become a part of the circuit itself. Digital and analog ammeter instruments are the most common type, and both utilize a separate or included jack in order to attach the test lead plug to the circuit. While ammeters are primarily designed for measuring current, many can still provide readings for voltage and resistance as well. As many models may differ from one another, it is best to refer to manufacturer specifications or the owner’s manual for how measurements may be conducted.

When an ammeter is connected to the circuit through its leads, current will pass through the device and a measurement is made. If there are no issues with the circuit, no voltage should be dropped during the process. The readings of digital and analog ammeters are slightly different, and many say that analog ammeters are more difficult to read. Despite this, the continuous movement of the needle across the indicator dial allows for a more thorough and precise measurement in regard to current changes. It is important to enact caution when conducting measurements with any ammeter, as a surge in current can damage the instrument and its components. As such, a meter may have a fuse or specific device settings to protect itself.

Ammeters are often compared to other measurement devices such as galvanometers, but the two should not be confused with one another. While the ammeter is used for measuring current, voltage, and resistance, the galvanometer is a mechanical device that indicates the magnitude and direction of current. Galvanometers are also not used for measuring alternating current, and they require a magnetic field in order to achieve their readings. As such, both devices are fairly similar in their ability to measure electronic circuit properties, though their different roles and characteristics set the two devices apart.

In the case that an ammeter needs to measure a system that exhibits an unsafe current level, the ammeter may be placed in parallel with a shunt resistor. A shunt resistor often comes in the form of a high precision manganin resistor that has a low resistance value. With this setup, the current is reduced by the shunt resistor before entering the ammeter, and a reading is obtained. As the voltage resistance is already known before conducting a measurement, the read value can be scaled back to the original amperage while ensuring the safety of the measurement device.

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