Magnetic Gauges
There are several types of magnetic gauges. The simplest form is the ammeter type (Figure 21-6). In which a permanent magnet attracts a ferrous indicator needle connected to a pivot point and holds it centered on the gauge. An armature, or coil of wire, is wrapped around the base of the needle near the pivot point. When current flows through the armature, a magnetic field is formed. This magnetic field oppose that of the permanent magnet. Attractive or repulsive magnetic forces cause the needle to wing left or right. The direction the needle swings depends on the direction of current flow in the armature.