C series Thomson DC meters (1904 to the 1930s?) Previous
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This meter used the same principles as the previous Thomson Recording Wattmeters but were made in a more compact and easier to handle enclosure. Like the preceding T.R.W. meters, the Type C meter came in several styles as well as a broad range of capacities from 5 to 10,000 amperes. Pictured below are two different styles of the C series DC meters. The one on the left is an early model that had the oval nameplate of the earlier Thomson Recording Wattmeters, and the second picture is the later version of the C series. The lower capacity versions were replaced in 1923 by the C-15 meter.
 
Early C series meter
David Turner Collection
Typical C series meter
Electrical Meterman's Handbook