Ammeter

—A device for measuring the number of amperes which are pa ing through a current and showing the same by direct reading on a scale. The ammeter is a commercial form of galvanometer in which the deflections (or twistings) of a magnetic needle are valued in amperes. Ammeters are made in various forms, based upon several different principles, among which are. (1) Permanent-magnet ammeters, (2) electro-magnet ammeters, (3) spring ammeters, (4) gravity ammeters. Many ammeters consist of moving coil mill i-voltmeters connected to the terminals of shunts through which the currents to be measured are pa ed. The shunts are made of a high resistance alloy, and since the resistance remains constant the drop in potential between its terminals will be proportional to the currents pa ing through the shunts. This type is used for direct currents only. For alternating currents the electro-magnetic system is generally employed