Lightweight, compact modular system that includes an acquisition photocell is used as a light source tracking detector that exhibits minimum scale factor change with increased light source angle. Photocells of various types, responsive to other portions of the spectrum, could be used to acquire and track infrared, ultraviolet, and other source fluxes

Carpenter, D. G.

Hooper, G. E.

English

NASA Technical Reports Server

December 1966
	 Brief 66-10564 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Photocell Shadowing Technique Improves Light Source Detector 
X Axis 
Shadowed 
Photocells 
WINE..!ItaJ M W,10 ^ —Oftsm.—Iffil V Axis 
Knife-Edge..-'
	 \\	 ////'	 Acquisition 
Apertures	 Photocell 
X Axis 
The problem: 
To design a light source tracking detector that ex-
hibits minimum scale factor change with increased 
light source angle. The tracking detector should be 
simple in construction and use standard, reliable com-
ponents. 
The solution: 
A lightweight, compact modular system that in-
cludes an acquisition photocell for seeking the light 
source and four shadowed photocells, two per (X and 
Y) axis.
How it's done: 
Operation of the tracking detector involves null 
sensing by two sets of two cadmium sulfide photocells 
operating in an X-Y configuration to act on a bridge 
circuit. These four cells are shadowed by knife-edge 
apertures that cause one cell in an axis to receive more 
luminous flux than the other as a function of tracker 
angular displacement. This results in an electrical 
offset in the bridge circuit proportional to the degree 
of angular displacement. A fifth, or acquisition cell, 
mounted in the center of the module, operates in con-
junction ith a s itching circuit to provide an acquire 
continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000562 2020-03-11T17:44:28+00:00Z
and intensity signal to discriminate between wanted 
and unwanted sources. Using two cells in each axis 
with opposite shadow edges, angular motion of the 
light sourée causes one cell to increase in resistance 
while the opposite cell resistance decreases, thus caus-
ing a pOsitive or negative voltage output in the bridge 
circuit. This output signal is processed to produce a dc 
output error signal that operates a servo system to 
return the detector to a null position by removing 
the pointing error. 
Notes: 
1. The bridge circuit plus signal processing electronics 
are packaged in the back portion of the tracker, 
thus making a small, lightweight unit.
2. Photocells of various types, responsive to other 
portions of the spectrum, could be used to acquire 
and track infrared, ultraviolet, and other source 
fluxes. 
3. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference B66-10564 
Patent status: 
No patent action is contemplated by NASA. 
Source: Gerald E. Hooper 
and Dennis G. Carpenter 
(JPL-809) 
Brief 66-10564	 Category 01


Photocell shadowing technique improves light source detector

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server