DC ammeter, or direct current ammeters, detect the current by measuring the current of the electron flow in an electrical unit. Ammeters are connected to the electrical unit as part of the circuit, but are never connected to a voltage source as the high charge could damage the ammeter.
When the electron current flows through the series, it is measured once it passes through the ammeter. This device is designed so that it does not output any current when activated; this allows for accurate readings of the electrical device's current only. Ammeters are similar to galvanometers, voltmeters and ohmmeters, which all are instruments used to detect currents in various ways.