Thomson Induction Wattmeter, Form C-4
(1898 to 1902)
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The Form C-4 was an improved version of the previous Form C, but was still quite primitive. The voltage circuit in this meter used an external reactance coil mounted behind the register (similar to the reactance coil as used in the early Ft. Wayne and Westinghouse meters). The coils and brake magnet were mounted on a platform underneath the disk (as opposed to the later practice of using a vertical frame). The only adjustment that is mentioned in the literature I have on this model was a light load adjustment that consisted of a copper shading strip between the poles of a starting coil. The cast metal cover of this meter (not shown) is very similar to the one used on the High Torque meter. Thomson Induction Wattmeter, Form C-4
GE Thomson Induction Wattmeter manual