Telemetry system modifications to improve signal resolution are described. Process uses zero suppression technique which consists of subtracting known voltage from input and amplifying remainder. Schematic diagram of circuit is provided and details of operation are presented

Grant, R. L.

Russell, W. A.

Scheer, M. L.

English

NASA Technical Reports Server

October 1972	 B72-10639 
NASA TECH BRIEF 
Marshall Space Flight Center
	 .4r 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription 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 1<1, Washington, D.C. 20546. 
A Range Expanding Signal Conditioner 
The problem: 
Existing signal conditioners used with a telemetry 
system limit the resolution to approximately 20 millivolts 
for a 0- to 5-volt signal. 
The solution: 
A range expanding signal conditioner improves the 
signal resolution by expanding the input in eight 0- to 
5-volt ranges. It accomplishes this by a combination of 
zero suppression and amplification. In addition to the 
increased resolution, the circuit provides a high degree of 
common mode and noise rejection. 
How it's done: 
The zero suppression technique consists of subtracting 
a known voltage from the input and amplifying the 
remainder. The zero suppression is in eight 0.625 volt 
steps with an amplification factor of 7.6, giving an 
effective full scale output of 38 volts. The accuracy of the 
fine output is 0.3 percent of the input and that of the 
coarse output is 2 percent. 
The figure is a simplified diagram of the circuit. The 
input stage accepts a differential input and yields a 
single-ended output. Two noninverting amplifiers in the 
input buffer provide a very high impedance to prevent 
Input	 Input	
•iui.	 Filter Buffer
loading of the signal source and to make the conditioner 
relatively independent of the source impedance. 
The filter, which consists of an amplifier and its 
associated components, provides most of the filtering for 
both the ac common mode and the noise signals passed by 
the buffer. The filter has two poles to insure that noise 
will not cause oscillations in the control logic or signifi-
cantly degrade the accuracy. The first pole has a break 
frequency of about 2 Hz, the second pole about 1.8 Hz. 
The overall attenuation of the network is greater than 100 
for inputs of 20 Hz, and rolls off at 40 dB per decade. The 
filter is operated at a gain of less than one to compensate 
for the gain of the input buffer. 
The summing amplifier receives a filtered and inverted 
replica of the input signal concurrently with one of seven 
discrete positive voltage levels generated in the variable 
reference. These are summed to provide zero suppression 
and are amplified to provide the scale expansion. The gain 
is set at 7.6 and the voltage from the variable reference is 
in 0.625-volt increments. 
The variable reference is a digital to analog converter 
(DAC) whose output is varied by +0.625-volt, via the 
control logic whenever the output of the summing 
amplifier equals +495 or 0 volts, respectively. The control 
circuitry varies the output of the DAC to maintain a 0- to 
5-volt output at the summing amplifier. 
Summing Fine Output 
Amplifier	
__
 
Coarse Output
Variable	 k	 Control Reference	 Logic 
Range Expanding Signal Conditioner
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use Government nor any person acting on behalf of the United States
	 will be free from privately owned riahts.
https://ntrs.nasa.gov/search.jsp?R=19720000638 2020-03-17T03:41:44+00:00Z
The input to the converter is reconstructed from the 
coarse and fine outputs in the following manner: 
(a) The coarse output (Vc) and the fine output (Vf) 
are measured and recorded. 
(b) Vc is divided by 0.625 and the quotient is 
recorded. 
(c) If Vf is greater than 4 volts, 0.5 is subtracted 
from the quotient (b). 
(d) The whole integer of result (c) is multiplied by 
0.625 volt and the product is recorded. 
(e) Vf is divided by 7.6 and the quotient is 
recorded. 
(f) The result of computations (d) and (e) are added 
to find the input voltage. 
Step (c) is necessary to account for the hysteresis in Vf. 
Notes: 
1. Information concerning this innovation may be of use 
in monitoring or in the expanded resolution of in-plant 
process functions.
2. No further documentation is available. Specific ques-
tions, however, may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B72-10639 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: W. A. Russell, R. L. Grant, and M. L. Scheer of

of McDonnell Douglas Corp.
under contract to
Marshall Space Flight Center

(MFS-2 1720) 
B72-10639	 Category 02


A range expanding signal conditioner

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