Electrodynamometer Movement:

The  electrodynamometer  movement  display in the figure has  the  similar  basic  operating  principle  as  the D'Arsonval meter movement, except in which the permanent magnet is replaced through fixed coils. The moving coil and pointer that are attached to the coil are suspended among and connected in series along with the two field coils. The two moving coil and field coils are linked in series such which the similar current flows by every coil.

Figure: Electrodynamometer Movement

Current flow by the three coils in either direction causes a magnetic field to be generates among the field coils. The  similar  current  flow  by  the  moving  coil  causes  it  to  act  as  a magnet exerting a force against the spring. The field polarity and the polarity of the moving coil reverse if the current is reversed, and the force continues in the same direction. Because of to this features of the electrodynamometer movement, it could be used in both AC and DC systems to measure current. A few voltmeters and ammeters use the electrodynamometer. Therefore, it's most important use is in the wattmeter that will be elaborate later in this module.