Attitude control system designed for rockets regulates duty cycle of pneumatic valves so less fuel is required. Operation time of each valve is directly proportional to error signal and the dead band about a null is controlled by independently adjustable threshold circuits

Cooke, W. A.

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December 1971	 B71-10497 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a aubscription basis from the National Technical Information 
Service, Springfield; Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Pulse Width-Pulse Rate Modulator
The problem: 
To control the duty cycle of the pneumatic valves 
associated with the attitude control system of rockets 
so that less fuel is required. 
The solution: 
A pulse width-pulse rate attitude control system 
wherein the operation time of each valve is directly 
proportional to the error signal and the dead band 
about a null can be controlled by independently ad-
justable threshold circuits. 
How it's done: 
The pulse width-pulse rate circuit which is the 
heart of the control system consists of an integrator 
and threshold switches to turn a pair of solenoid 
valves completely on or completely off. The integrator 
amplifier AR1 is a high-gain integrated circuit oper-
ational amplifier with two negative feedback loops 
that convert it to a pulse width-pulse rate modulator. 
The output of this amplifier drives two threshold 
switches, each consisting of identical integrated cir-
cuit differential comparators with an hysteresis that 
is a function of positive feedback; when the input 
exceeds a predetermined level, the output switches. 
When an input signal is applied to the circuit, the 
signal is integrated by AR1 to a predetermined thres-
hold level. The inverted output of the integrator is 
a positive- or negative-going ramp which rises or 
falls at a rate that is directly proportional to the in-
put signal, either positive or negative. 
A positive and a negative reference voltage is 
applied to threshold switches AR2 and ARS, respec-
tively. With a positive input signal applied, thres-
hold circuit AR3 switches when the output of the 
Adelk	 (continued overleaf) 
Now
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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=19710000494 2020-03-17T02:26:26+00:00Z
integrator reaches the AR3 threshold. The output of 
AR3 turns off transistor Q3 which causes a voltage 
of opposite phase to appear at the input summing 
junction. This causes the integrator output to reverse 
direction. The output pulse stays on until the inte-
grator output goes below the threshold trigger point. 
Because of threshold hysteresis, the output pulse can 
be made to stay ON for some predetermined length 
of time. Operation of threshold switch AR2 is iden-
tical to AR3 except that inversion of the AR2 output 
is not necessary. 
Diodes CR2 and CR3 are reverse-biased under 
no-signal conditions, preventing the voltage at the 
output of AR2 and Q3 from appearing at the sum-
ming junction, which produces minimum integrator 
offset. Zener diodes VR1 and VR2 limit the minimum 
signal that can be applied to AR2 and AR8. A small 
positive potential is developed at Q3 source by CR1 
and R6.
Note: 
Requests for additional information may be di-
rected to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP- 71-10497 
Patent status: 
No patent action is contemplated by NASA. 
Source: Walter A. Cooke of

Lockheed Missiles & Space Company

under contract to

Ames Research Center 
(ARC-10025)
. 
B71-10497 Category 01


Pulse width-pulse rate modulator

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