Piezo-bar pressure type probe measures the impact velocity or pressure of a moving debris cloud. It measures pressures up to 200,000 psi and peak pressures may be recorded with a total pulse duration between 5 and 65 musec

Friend, W. H.

Murphy, C. L.

Shanfield, I.

English

NASA Technical Reports Server

Flexible Wire	 Brass Casing	 Quartz Crystal	 Rubber 0-Ring -	 , - hylene Washer 
July 1967
	
Brief 67-10259 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
A Piezo-Bar Pressure Probe 
Back Reflection Bar	 Flexible Ground 
	Tungsten Or Steel 
The problem: 
To measure the impact velocity or pressure of a 
moving cloud consisting of a heterogeneous mixture of 
solid particles and gas molecules. When a high-speed 
pellet, propelled by a hot gas stream, strikes a thin 
sheet target, an impact cloud is generated. This gas/ 
debris cloud results from the fragmentation of the 
solid components which in turn mix with the propel-
ling gas stream. Such an expanding high velocity (of 
the order of 15 kilometers per second) cloud, consist-
ing of very small particles associated with high-tem-
perature gas is highly erosive; consequently, commer-
cial piezoelectric transducers could not be expected to 
survive in such an environment. 
The solution: 
A piezo-bar pressure-type probe for measuring pres-
sures up to 200,000 psi within the impact-generated 
debris cloud. Its construction is similar to that of 
other piezoelectric pressure-bar instruments. Peak 
pressures may be recorded with a total pulse duration 
between 5 and 65 jzsec. 
How it's done: 
The pressure sensing elements of the probe, the 
pressure bar, the quartz crystal, and the back reflec-
tion bar are supported within a two-piece brass outer 
casin g by polyeth ylene washers and rubber 0-rings.
The washers and 0-rings provide radial support for 
the sensing elements plus electrical and acoustical 
isolation from the outer casing. 
A pressure pulse incident on the measuring end 
of the bar causes a local strain (stress) that travels 
down the bar in the form of a wave at a velocity equal 
to the acoustic response of the bar. When this wave 
passes through the piezoelectric crystal element, it 
strains the element causing a signal to be generated in 
the form of an electrical charge. The magnitude of this 
charge is proportional to the magnitude of the pres- 
sure force exerted on the pressure bar and transmitted 
by it to the crystal element. The rear face of the back 
reflection bar is restrained axially by a light spring that 
permits essentially free axial motion of the sensing 
system. All of the momentum transferred to the pres- 
sure bar by the gas cloud is thereby retained in the 
bar/crystal system for a period greater than the useful 
linear response period of the probe. 
Note: 
Inquiries concerning this innovation may be di- 
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B67-10259 
-	 (continued overleal) 
This document was prepared under the sponsorship of the National 
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=19670000259 2020-03-11T20:33:31+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: W. H. Friend, C. L. Murphy, 
and I. Shanfield 
of McGill University 
under contract to 
Lewis Research Center 
(Lewis-393) 
Brief 67-10259	 Category 01


A piezo-bar pressure probe

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