A Photoelectric Method for Tracing Current Wave Forms

Abstract

A photoelectric timing circuit arrangement has been designed to obtain point by point plots of periodically varying currents. The circuit employs a three‐electrode vacuum photo‐tube in which electron emission occurs only when a sudden light flash enters the cell through a narrow slit in a disc driven by a synchronous motor. A noninductive resistance carrying the current to be measured is inserted in the grid circuit of the photo‐triode. The electron emission registered by a galvanometer in the collector circuit is completely controlled by the momentary value of the potential set up in this resistance by the current at the instant of the light flash. In this manner, by changing the time at which the light flash occurs in the current cycle, a complete delineation of the current wave form is secured. The method eliminates distortion in wave form introduced by mechanical oscillographs and by amplifiers used with cathode ray oscillographs when small currents or potentials are to be measured.