Ammeter through a wire which expands as it heats. Although these instruments have slow response time and low accuracy, they were sometimes used in measuring radio-frequency current. These also measure true RMS for an applied AC. In much the same way as the analogue ammeter formed the basis for a wide variety of derived meters, including voltmeters, the basic mechanism for a digital meter is a digital voltmeter mechanism, and other types of meter are built around this. Digital ammeter designs use a shunt resistor to produce a calibrated voltage proportional to the current flowing. This voltage is then measured by
Manganin Manganin Manganin is a trademarked name for an alloy of typically 84% copper, 12% manganese, and 4% nickel. It was first developed by Edward Weston in 1892, improving upon his Constantan (1887). Manganin foil and wire is used in the manufacture of resistors, particularly ammeter shunts, because of its virtually zero temperature coefficient of resistance value and long term stability. Several Manganin resistors served as the legal standard for the ohm in the United States from 1901 to 1990. Manganin wire is also used as an electrical conductor in cryogenic systems, minimizing heat transfer between points which need electrical connections.