Thomson Recording Wattmeter
(1892 to 1910s)
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Shortly after the merger of Edison General Electric and Thomson-Houston Electric, the T.R.W. was redesigned slightly and continued with a few changes along the way over the next few years. The T.R.W. was a commercial success, many of the early electric utilities quickly standardizing on this model. Initially, this meter was available in numerous styles covering the whole spectrum of applications from 3-amp models for smaller residential loads to models rated up to 1200 amps for heavy DC power circuits. There were also high-voltage versions made for metering the output of DC and AC arc-lamp generators. For AC applications, some were made for use with current and potential transformers to meter high-voltage / current circuits and (with appropriate resistance or reactance boxes) on balanced polyphase circuits. With the introduction and rapid acceptance of induction-type meters in the late 1890s (starting with Westinghouse's Shallenberger watthour meter and GE's Form C Induction Wattmeter), the T.R.W. was quickly relegated to use on DC circuits. In fact, the T.R.W. was the only commercially available DC meter for a few years until other manufacturers started making DC meters in the early 1900s. In 1904, the T.R.W. was superseded by the Type C Thomson DC watthour meters, but a few T.R.W.s were made into the 1910s.
 
Thomson Recording Wattmeter
Don Price collection