Electronically measuring the transit time of a soap bubble carried by the gas stream between two fixed points in a burette calibrates flowmeters used for measuring low gas-flow rates

Copeland, A. C.

Fulton, W. C.

Smither, M. A.

English

NASA Technical Reports Server

May 1965	 Brief 65-10137 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Instrument Calibrates Low Gas-Rate Flowmeters 
Optical Axis Marked 
Burette -..
-	 On Burette for Alignment 
Gas Outlet	
0 
Light Bulb Photodiode 
Light Bulb Power Supply	
.._i__.1.;3E:1._l 	 -	 Bulb	 - 
Photoduode Output Terminals 
Burette
Arnplifie.r and	 DETAIL OF SECTION 
Shaoina Circuits 
I Gas In	 Counter - 
is SurgeTank	 Soap
Power 
Soap Solution
Rubber Bulb 	
Bubble Supply 
The problem: Calibrating flowmeters used for 
measuring low gas-flow rates (60 to 1000 milliliters 
per minute). 
The solution: Electronically measuring the transit 
time of a soap bubble carried by the gas stream be-
tween two fixed points in a burette. 
How it's done: A light source and a photodiode 
are positioned on opposite sides of each of two fixed 
points on a graduated burette. Soap bubbles are in-
jected into the gas stream by squeezing a rubber bulb 
connected to a soap solution at the bottom of the bu-
rette. The first bubble to enter the burette cuts off the 
light beam from the lower photodiode which then trig-
gers a pulse to an amplifier. The amplified pulse is fed 
to a Schmitt trigger circuit which applies a narrow 
square-wave pulse to a- flip-flop circuit connected to a 
digital counter. (Once the flip-flop circuit is turned on, 
it is insensitive to pulses generated by succeeding bub-
bles.) The digital counter times the passage of the bub-
ble through the burette until it passes the light beam
at the upper photodiode. At this time, another pulse is 
generated and fed through' a second amplifier and 
shaping circuit to a flip-flop circuit, which applies an 
off pulse to the counter. The counter reading indicates 
the transit time of the bubble between the two fixed 
points on the burette. Since the distance between these 
points and the cross-sectional area of the burette are 
accurately known, the gas flow rate is readily 
computed. 
Notes: 
1. This experimental system has been used to measure 
low gas-flow rates with an accuracy of better than 
one percent. 
2. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas, 77001 
Reference: B65-10137
(continued overleaf) 
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=19650000136 2020-03-11T17:22:32+00:00Z
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C., 20546. 
Source: Miles A. Smither, Wm. C. Fulton, 
and Albert C. Copeland 
(MSC-134)
is 
[1 
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Brief 65-10137	 Categories No. 01 and 02


Instrument calibrates low gas-rate flowmeters

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