Ammetern

Ammetern is an instrument used to measure electric current in a circuit, expressed in amperes (A). It is designed to be placed in series with the load so that the same current flows through it as through the circuit being measured. In practice, ammeters are found in laboratory instruments, power supplies, automotive dashboards, and multimeters.

Most ammeters work by producing a signal that is proportional to the current. Shunt-based ammeters use a low-value precision resistor in series; the small voltage drop across the resistor is measured and converted into a current reading. Other designs rely on a magnetic mechanism, such as a moving-coil or moving-iron meter. Modern ammeters often use solid-state sensors and display the result digitally, and some are true-RMS for alternating current.

Types of ammeters include shunt ammeters, moving-coil or moving-iron analog meters, clamp-on ammeters based on a current transformer, and Hall-effect ammeters that can measure DC and AC without a direct electrical connection. Clamp meters, in particular, can measure high currents without interrupting the circuit.

Key considerations for ammeters are burden voltage and accuracy. The device should have as small a resistance as practical to minimize disturbance to the circuit. Accuracy classes vary, with typical digital meters offering around 0.5–1.5% and additional offset or nonlinearity errors in some models. Range selection and proper calibration are essential for reliable readings.

Etymology and history trace the term to the ampere, the SI unit of current, and reflect the evolution from galvanometer-based indicators to modern digital sensing. Ammeters are essential tools in electronics, electrical engineering, and diagnostics.