A stroboscopic method of testing watthour meters

W. B. Kouwenhoven: The method described by Mr. Sparkes is very ingenious. The arrangement that he has provided, for changing the speed of his flashing lamp so as to bring it into synchronism with the marks on the meter disk, makes it possible to use the device to check over a wide range of speed. The method should give accurate results, as the torque of the wattmeter measuring the a-c. load, is balanced by the torque of a d-c. voltmeter element supplied with current from a magneto driven from the flasher shaft. Care must be taken to see, that the armature reaction of the magneto is negligible, otherwise errors may be introduced.