ammeter

noun

1. A device that measures the magnitude of an electric current, especially one calibrated in amperes.

   “The controllers of these diesels do not move round in notches, so that the driver's only sure guide to the way in which he is working his locomotive is his ammeter, corresponding in a way to the steam-chest pressure gauge of a steam locomotive. When the diesel was being worked full out, the ammeter normally showed about 1,500-1,600 amps, with occasional surges of current at starting or up the steepest gradients to 1,700 or even 1,800 amps.”