M (1912, 1913) Previous
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This model had all the major base pieces made from punched steel (base, terminal chamber, mounting frame, inner frame, etc.). Unlike other AC meters, the 90 degree lag of the Model M's voltage coil was accomplished by using a second air gap on the voltage coil and utilizing the reactance of the disk. The light load adjustment was also unconventional, as it consisted of small iron cores on sliders in front of the potential coil cores that were positioned to obtain the light load adjustment. The full load adjustment was a little more conventional, consisting of an iron disk that could be adjusted relative to the retarding magnet air gap. Duncan M
Electrical Meterman's Handbook