Stable ac phase and amplitude comparator detects excessive vehicle maneuvering or vibration. It has phase demodulation, low-pass filter, and multiple threshold-setting capability designed specifically for low drifts over a wide range of temperatures

Bruce, H. P.

English

NASA Technical Reports Server

Reference 
Input 
Signal 
Input
-C'
old 
Threshold 
Output 
November 1967
	 Brief 67-10459 
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. 
Stable AC Phase and Amplitude Comparator 
The problem: 
To design a comparator circuit that will detect ex-
cessive vehicle maneuvering or vibration. Since the 
allowable vehicle vibration or maneuvering changes in 
accordance with the particular phase of the mission, 
multiple preselected thresholds are required. The 
monitoring elements are the rate gyros. They generate 
an ac output amplitude proportional to the rate of 
change of position. The phase of the output (0 or 
180 degrees) is determined by the direction of the 
change of position. Therefore, vibration of the ve-
hicle will generate a phase-modulated gyro output, 
and the frequency of the modulation will be the fre-
quency of vibration. Control signal processing of rate 
integrating gyros for missile and satellite applications 
require very low drifts over an extreme temperature 
range.
The solution: 
A stable ac phase and amplitude comparator with 
phase demodulation, low-pass filter, and multiple 
threshold-setting capability designed specifically for 
low drifts over a wide range of temperatures (-550 
to + 125°C). Differential operation of the comparator, 
from input through threshold detection, prevents 
drifts with respect to ground from affecting the 
threshold adjustments. 
How it's done: 
The comparator is designed to provide an output 
if the ac input exceeds a predetermined amplitude 
within a specified frequency range of phase modula-
tion. The differential output of amplifier No. I pro-
vides two ac inputs to transmission gates A and B. 
The reference amplifier outputs are used as gate-
enable signals for gates A and B. Operation of the 
(continued overleal) 
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=19670000459 2020-03-11T20:55:40+00:00Z
gates on the outputs of amplifier No. I provides two 
phase-sensitive, full-wave inputs, 180 degrees out of 
phase, to amplifier No. 2. This amplifier filters the 
phase-demodulated signals, providing a differential 
output. The amplitude and polarity of this output will 
be determined by the amplitude and phase of the 
input as long as the phase-modulation frequency is 
within the bandpass of the amplifier filters. As the 
modulation frequency increases, the amplifier output 
will decrease according to the frequency attenuation 
characteristics of the filters. The gate generator is a 
saturable switch that enables the differential outputs 
of transmission gates C and D to be always the same 
polarity regardless of the polarity of the inputs from 
amplifier No. 2. Amplifier No. 3 is a buffer amplifier 
used to provide adequate isolation so that a reference 
voltage can be floated on one side of the differential 
output. The inputs to amplifier No. 4 have an offset 
voltage determined by the potentiometer setting from 
zero to the maximum voltage of the reference source. 
As the comparator input amplitude increases, the off-
set voltage decreases, until the offset voltage is ex-
ceeded, changing the output polarity of amplifier No. 
4.
The threshold levels may be changed by switching 
St or by adding other amplifiers and potentiometers, 
connected like amplifier No. 4, for each reference 
voltage setting desired. A relay driver at the output 
of amplifier No. 4 may be used to provide isolation 
of the load from the comparator. 
Notes: 
1. Suggested applications for this comparator are 
advanced control-signal processor, a rate switch 
control-signal processor, and a rate switch. 
2. Inquiries concerning this development may be di-
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10459 
Patent status: 
No patent action is contemplated by NASA. 
Source: H. P. Bruce 
of the Martin Company, 
under contract to 
Marshall Space Flight Center 
(M FS- 13086) 
Brief 67-10459	 Category 01


Stable ac phase and amplitude comparator

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server