Servo amplifier feedback system, in which the phase sensitive detection, low pass filtering, and multiplication functions required for quadrature rejection, are preformed by light-controlled photoresistors, eliminates complex circuitry. System increases gain, improves signal-to-noise ratio, and eliminates the necessity for compensation

Mc Cauley, D. D.

English

NASA Technical Reports Server

December 1967	 Brief 67-10552 
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. 
Light-Controlled Resistors Provide Quadrature Signal Rejection for

High-Gain Servo Systems 
T2 
The problem: 
To develop a simple, reliable servo amplifier feed-
back circuit to reduce the quadrature components at 
the output of a high-gain servo system. Quadrature 
signal components may cause overheating of the servo 
motor, and thus they must be eliminated before pass-
ing through the final servo amplifier. 
The solution: 
A servo amplifier feedback system, in which the 
phase sensitive detection, low pass filtering, and multi-
plication functions required for quadrature rejection, 
are performed by light-controlled photoresistors. 
How it's done: 
The voltage applied to the servo motor is also ap-
plied to the transformer Ti, and is added vectorially
to the output of T2 in a bridge circuit. Any quadra-
ture signal component existing in the motor drive 
voltage causes an unbalance in the light-controlled 
resistor bridge circuit. When the quadrature voltage 
is zero, the respective voltages to the lamps in the 
light-controlled resistors are equal and both the light-
controlled resistor bridge and resistor bridge are 
balanced. 
When a quadrature component does exist in the 
servo loop, the vector relationships produce unequal 
magnitudes of voltages to the lamps, and the light-
controlled resistor bridge becomes unbalanced. This 
unbalance causes a corresponding - unbalance in the 
resistor bridge and applies a quadrature voltage to 
the transformer T3. Transformer T3 is connected so 
that the quadrature voltage applied to the error volt-
(continucd overleat) 
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=19670000551 2020-03-11T20:58:47+00:00Z
age is in opposite phase with respect to the quadra-
ture component of the error signal, and they there-
fore cancel each other. 
Notes 
1. This quadrature rejection circuit provides other 
advantages in addition to the reduction in the com-
plex circuitry normally required for high-gain 
servo feedback systems. These advantages are: 
increased gain, improvement of signal-to-noise 
-ratio, and elimination of necessity for compensa-
tion.
2. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Western Support Office 
150 Pico Boulevard 
Santa Monica, California 90406 
Reference: B67-10552 
Patent status: 
No patent action is contemplated by NASA. 
Source: D. D. McCauley 
of Philco 
under.
 contract to 
Western Support Office 
(WSO-340) 
Brief 67-10552	 -	 -	 Category 01


Light-controlled resistors provide quadrature signal rejection for high-gain servo systems

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