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Graphic InstrumentsAuthor: E.E. Kimberly Graphic instruments draw curves for a permanent record of the variation of current, voltage, power, power factor, etc. with time. For every electrical indicating instrument, there is a corresponding graphic or curvedrawing instrument. These instruments are highly useful in analyzing factory loads and loads of individual machines. A graphic voltmeter and ammeter may show that a motor overheats because the line voltage is allowed to become too low and the current therefore becomes too great. A graphic wattmeter may show that the load on a motor reaches the fullload value of the motor rating for only 10 minutes in every hour and does not exceed halfload in the other 50 minutes. An induction motor so loaded runs at a lower power factor and efficiency, and should be replaced with one that is nearer the correct size and represents less invested capital.


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