Sensor with no moving parts measures carbon dioxide partial pressures of 0 to 40 mm Hg for total pressures up to 14 psia with a full scale accuracy of 5 percent

Mc Henry, T. F.

English

NASA Technical Reports Server

Primary 
Detecto 
- Compei 
Detecti 
Optical 
- Pickoff 
For Corr 
Beam 
Splitter 
Filter, 
Source
Filter, F1 
SECTION A-A 
I f 
rUIq 
Mirror
.........
F liter ,F1/
December 1971
	 Brief 7 1-1053 6 
.-
NASA TECH BRIEF 
Manned Spacecraft 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 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 KT, Washington, D.C. 20546. 
Miniature Carbon Dioxide Sensor 
Sample Chamber	
A7 
Figure 1. Schematic of Optical Configuration 
A miniature sensor with no moving parts measures 
carbon dioxide partial pressures of 0-40 mm Hg for total 
pressures up to 14 psia with a full scale accuracy of 5%. 
The sensor compares the radiation received in two spec-
tral regions, one of which is absorbed by carbon dioxide. 
The 4.3 micron region is used as the absorbing channel 
since the absorption is strong in this region, and the 
4.0 micron region is used as the other channel since it 
corresponds to an atmospheric window with no sub-
stantial infrared absorption. An infrared detector is posi-
tioned to detect radiation from the two spectral regions 
alternately. When a signal occurs it corresponds to car-
bon dioxide absorption and accordingly carbon dioxide 
concentration. 
Figure 1 illustrates the optical mechanical con-
figuration. The sources, S 1
 and S2 , are provided with 
filters F 1 and F2
 which are centered at 4.3 and 
4.0 microns respectively. The sources are alternately 
switched on by an astable multivibrator source switch 
as shown in the schematic of Figure 2. Radiation is 
Am	
(continued overleaf) 
Now
This documetct 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.rights. 
https://ntrs.nasa.gov/search.jsp?R=19710000526 2020-03-17T02:26:52+00:00Z
	D	 K	 ______________	 Synchronous	 1-	 —D• Output 
	
i	 I	 Demodulator 
Gain 
	
Adjust	 I 
	
Astablek	
Synchronou s 
S2 
(	 )	
Multivibrtor	 From Source 
Inputs 
	
Source	 I	 Switch 
	
Switch	 I 
 Synchronous	 I	 Error
K^>^ 	 Demodulator	 f 	
Goes To 
Zero 
Source Balancing Circuit 
G- Error Signal Balances Sources 
Figure 2. Schematic of Measurement Circuitry 
directed by a beam splitter, B 1 , made of a thin piece 
of germanium through a window, W 1 , to a spherical 
mirror. The area between the window and the mirror 
is the sample,chamber containing air and carbon dioxide. 
The mirror images detector D 1 on the apparent 
source. The compensating detector D 2 is imaged on the 
sources through the beam splitter via the optical pickoff. 
Radiation from S 1 and S2 detected at D 1 is amplified 
and synchronously demodulated to produce an output. 
If no carbon dioxide is present, D 1 views essentially the 
same sources and the output is zero. If carbon dioxide 
is present, the difference in the incident signals pro-
duces an output from which the carbon dioxide concen-
tration can be calculated. Radiation from S 1 and S2 is 
also alternately applied to the compensating detector D2 
whose output is amplified and synchronously demodu-
lated. If the sources are matched there is no output but 
if there is a difference in the radiation from S 1 and S2, 
error signals are produced and fed back to the source S 
to produce a null and match source intensities. 
This information should be of interest to those 
organizations concerned with environmental monitoring 
and control.
Note:
Requests for further information may be directed 
to:
Technology Utilization Officer 
Manned Spacecraft Center, Code JM7 
Houston, Texas 77058 
Reference: TSP71- 10536 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by NASA. 
Inquiries concerning license rights should be made to: 
Patent Counsel 
Code AM 
Manned Spacecraft Center 
Houston, Texas '77058 
Source: Thomas F. McHenry

Barnes Engineering Company
under contract to

Manned Spacecraft Center
(MSC-13332) 
Briel' 71-1053(
	
Category 03


Miniature carbon dioxide sensor

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