GB1104756A - Improvements in methods and apparatus for phase comparison - Google Patents

Abstract

1,104,756. Photo-electric control system. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 28, 1965 [June 29, 1964], No. 26855/64. Heading G1A. In a method of measuring a variable quantity such as the angular displacement of an output shaft of a machine by comparing it with a fixed or variable reference value, e.g. the angular displacement of an input shaft, an A. C. signal representing either the value or the quantity is applied to intensity modulate a modulatable light-source optical gratings are caused to move relatively to one another in accordance with either the quantity or the value respectively, and the output of a photo-cell illuminated by the source through the gratings provides a signal representing the difference between the quantity and the value. The amplified output from a photo-cell PE1, Fig. 2, actuated by a tungsten lamp TL1 through a driven radial grating RG1 and an index grating IG1, is applied to a gallium arsenide lamp GAL serving as a source to a similar pair of gratings coupled to an output shaft. The rectified output of photocell PE2 of the last named gratings provides an error signal for control or other purposes. The motion of a single body, rotary or linear, may be controlled by an oscillator output or by a recorded signal being used to modulate the light-source of a pair of gratings one of which is coupled to the body. The phase of the modulation relative to the photo-cell output should be such as to produce maximum signal on departure from zero error.