Thomson-Houston Recording Wattmeter
(1889 to 1892)
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After Thomas Edison came up with his chemical meter in the late 1870s, he came up with the idea for a motor-type meter. However, since he preferred the chemical meter, he did not do any further work on it. In the mid-1880s, Elihu Thomson (likely with the help of Thomas Duncan) took this design, improved on it, and ended up with the first version of his 'recording wattmeter'. This meter was designed to work on both alternating and direct current and was much more rugged and accurate than other meters available at the time. The first picture shows an early prototype of the T.R.W., and the other two pictures are of an early production unit. The register on these early TRW meters is porcelain instead of the painted face found on the GE version.
 
T. R. W. prototype
Yardstick for Power: 50 years of Sangamo meters
Thomson Recording Wattmeter
Watertown Municipal Utilities collection
Thomson Recording Wattmeter
Watertown Municipal Utilities collection