Photoelectric detection system
Abstract
A photoelectric beam system for the detection of the arrival of an object at a discrete station wherein artificial light, natural light, or no light may be present is described. A signal generator turns on and off a signal light at a selected frequency. When the object in question arrives on station, ambient light is blocked by the object, and the light from the signal light is reflected onto a photoelectric sensor which has a delayed electrical output but is of the frequency of the signal light. Outputs from both the signal source and the photoelectric sensor are fed to inputs of an exclusively OR detector which provides as an output the difference between them. The difference signal is a small width pulse occurring at the frequency of the signal source. By filter means, this signal is distinguished from those responsive to sunlight, darkness, or 120 Hz artificial light. In this fashion, the presence of an object is positively established.
- Publication:
-
NASA Marshall Space Flight Center Report
- Pub Date:
- March 1982
- Bibcode:
- 1982msfc.rept.....C
- Keywords:
-
- Detection;
- Fabrication;
- Light Emitting Diodes;
- Manufacturing;
- Photoelectric Cells;
- Process Control (Industry);
- Background Radiation;
- Patents;
- Phototransistors;
- Signal Analysis;
- Signal Detection;
- Electronics and Electrical Engineering