Optic system coupled to an electronic detection and measuring system converts angular movement of reflected light to a direct readout, without any direct contact with the object

Davis, W. T.

English

NASA Technical Reports Server

March 1965
	 Brief 65-10073 
NASA TECH BRIEF H 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
System Measures Angular Displacement Without Contact 
Baffle _______	 Light  
SourceReadout 
Galvanometer 
_f_...c.-.Mftrorl Measurin]-*—] D.C. 
Amplifier 
Bar   I 
I 
Mirror	
Photo	
System - 
Cell 
The problem: To accurately measure the angular 
displacement of an object without the use of electrical 
or mechanical connection to the object. 
The solution: A system of optics coupled to an 
electronic detection and measuring system whereby 
angular movement of reflected light is converted to a 
direct readout. 
How it's done: The measuring system is based on 
the well-known optical lever principle and uses a 
photocell, amplifier, and galvanometer to provide the 
electrical readout. A mirror mounted on the test ob-
ject under observation reflects light from a fixed 
source to the detection system. As the object vibrates 
or rotates, the light beam reflected from the attached 
mirror sweeps through an angle equal to twice the 
angle by which the object is displaced. This light beam 
is reflected from a second mirror and focused on the 
edge of a photocell. The second mirror is mounted on 
a galvanometer and its attitude is a function of gal-
vanometer current. A change in the angle of the test 
object causes a corresponding change in the amount 
of light striking the photocell and thus a change in 
the output current of the photocell. This current is fed 
to the amplifier, measuring system, and readout and is 
used to deflect the galvanometer mirror to maintain 
the light beam in a position locked 
on 
the edge of the 
photocell. The current flowing through the loop is 
therefore a measure of the angle of the test object. 
Notes: 
I. This system has given accurate measurements to 
within 0.1 percent over a frequency range from dc 
to several thousand cps. 
2. In conjunction with servos, this system could be 
used effectively to maintain relative attitude of two 
or more items in severe environments. 
3. Application examples include fatigue tests in 
vacuum chambers, flutter research, damping meas-
urements, and control systems requiring deflection 
input.
(continued OverIet) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19650000072 2020-03-11T17:17:47+00:00Z
4. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia, 23365 
Reference: B65-10073
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to
	 40 NASA, Code AGP, Washington, D.C.., 20546 
Source: W. T. Davis 
(Langley-46) 
Brief 65-10073	 Category No. 01


System measures angular displacement without contact

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