moving magnet instrument
In most movements, the rotation of the pointer is triggered by magnetic induction: a current-carrying moving coil can rotate in the magnetic field of a permanent magnet, as in moving-coil movements and electrodynamic movements, or an iron part moves in a magnetic field, as in moving-iron movements, or a permanent magnet, as in rotary-magnet movements.
In the rotary magnetic movement, a permanent magnet moves in a magnetic field of a stationary coil. The magnetic field of the coil changes with the current flow and thus deflects the permanent magnet. The magnetic field lines acting on the permanent magnet provide the torque.
In addition, the rotating permanent magnet is acted upon by a fixed directional magnet, whose magnetic field lines provide the counter-torque and the rest position. The direction in which the pointer instrument deflects depends on the direction of the current through the coil, the angle is non-linear with the current.
Rotary magnetic movements are only suitable for direct current measurements.