An oscillator circuit and a thermistor, in close proximity to a light bulb, periodically alter the heat output of the bulb by varying the voltage across its filament. Use of this simulator permits checkout tests on pneumographs

Thomas, J. A.

English

NASA Technical Reports Server

+24V DC
lance 
nograph 
Switch 
November 1964	 Brief 64-10255 
NASA TECH BRIEF	
-I& 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint 
industry with the technical content of an innovation derived from the space program. 
Electronic Device Simulates Respiration Rate and Depth 
The problem: Instrumentation used on a space 
vehicle for measuring an astronaut's physiological 
functions includes an impedance pneumograph for 
measuring both his rate of respiration and the cyclic 
change in depth of his chest (thorax) accompanying 
respiration. The output signal from this instrument, 
which is a function of the changing dc impedance 
(resistance) across electrodes on the subject's chest, 
is telemetered to monitoring equipment on the earth. 
In order to permit checkout tests on pneumographs 
without the use of human subjects, it was necessary to 
design a simulator that would provide a cyclically 
varying resistance corresponding to the varying resist-
ance across the electrodes on a subject's chest. 
The solution: An oscillator circuit and a thermistor 
that is in close proximity to a 24-volt light bulb
in the oscillator circuit, but not physically connected 
to it. The periodically varying thermal output of the 
light bulb correspondingly varies the resistance of the 
thermistor. 
How it's done: The simulator employs a circuit 
consisting of a unijunction relaxation oscillator, an 
amplifier stage, a driver stage, a 24-volt dc power 
supply, and a small 24-volt light bulb. A thermistor 
connected in parallel with a switching circuit contain-
ing a number of resistors is placed in close proximity 
to the light bulb. 
In operation, the oscillator circuit periodically 
varies the heat output of the light bulb by varying the 
voltage across its filament. The frequency of the 
thermal variation is adjusted by means of poteritiom-
eter R . Potentiometer R2 can be adjusted to change 
(continued overleat) 
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=19640000068 2020-03-11T17:04:21+00:00Z
the amplitude (maximum temperature range) of the 
light bulb's output. The heat flux intercepted by the 
thermistor causes its resistance to vary in conformance 
with the variation of the thermal output from the bulb. 
As a consequence, the resistance at the output ter-
minals of the parallel thermistor-resistor network will 
vary in the same way. The selector switch in this 
network can be adjusted to compensate for environ-
mental temperature changes, so that the resultant 
resistance to the pneumograph input will remain 
effectively dependent only on the cyclic variations of 
the thermistor resistance. 
Notes: 
1. This simulator can be used for laboratory testing 
of electronic equipment other than pneumographs 
where a cyclic resistance variation is required.
2. The manual resistance-switching circuit can be 
replaced with a circuit that provides automatic 
temperature compensation. 
3. A related innovation is described in NASA Tech 
Brief B64-10259, November 1964. Inquiries may 
also be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas, 77001 
Reference: B64-10255 
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: James A. Thomas 
(MSC-89) 
Brief 64-10255	 Category No. 01


Electronic device simulates respiration rate and depth

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