Columbia Type SA DC switchboard meter (1910s) Previous
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This meter was made for use with shunts on high-capacity DC circuits but had an unique internal design. The rotor had 3 disks, the lowest serving as the regular brake disk which operated between 4 astatically arranged magnets. The upper two, surrounded the main armature coils which had a thin piece of steel going through each coil. The strip of steel extended from the underside of the top disk, down through an armature coil, and out along the top of the lower disk. This served to conduct the flux between the 4 series coils surrounding the upper disks and the armature coils. Also, the light-load adjustment was very similar to the tapped resistor used in the Type D. The lower bearing on this model, as with other high-capacity meters, was a cupped diamond. Some later examples of this model are marked as being made by the Roller-Smith Co., so there may be a connection between the two companies. Columbia switchboard meter
Electrical Meterman's Handbook