Strain-gage spacer probe uses the deflection of a leaf spring to measure strain in a long, slender beam nondestructively. The selected gage is of the smallest practical size, as thin as possible and yet of a standard type

Kolba, V. M.

Vetter, D. L.

English

NASA Technical Reports Server

August 1969.	 Brief 69-10343 
•1 Y C
AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Design of a Strain-Gage Probe 
The problem: 
Rapid and accurate measurement of long, slender 
channels by nondestructive means. High perform-
ance by a reactor core depends on very close di-
mensional control of various components and as-
semblies. For example, a constant flow of coolant 
through the fuel elements is required to balance the 
rates of generation and removal of heat, and ex-
cessive variations in channel spacings pose serious 
hydraulic and heat-transfer problems. Thus the im-
position of close tolerances for maintenance of chan-
nel dimensions requires accurate methods for meas-
urement of these dimensions. 
The solution: 
A strain-gage spacer probe using the deflection of 
a leaf spring to measure strain in a long, slender 
beam nondestructively. Reported accuracies of meas-
urement with two probes of a 0.037-inch channel 
were ± .0005 and ± .001 inch. With further develop-
ment, accuracies should exceed .0005. 
How it's done: 
The test probe consists of the strain gage and the 
required structure to position the gage, fix the rela-
tive locations of the components, and provide for 
movement. One type of probe has been used to 
measure the spacing between flat simulated fuel plates. 
The strain gage is bonded to a 0.003-inch-thick 
leaf spring that is spot welded to a 0.006-inch-thick, 
0.5-inch-wide flat steel strip. A thin cover strip, 
which protects the strain-gage leads, is spot welded 
to the steel strip. When this assembly is inserted be-
tween the fuel plates, deflection of the leaf spring 
produces a strain in the spring and strain gage. The
changes in strain-gage resistance are a function of the 
spacing between leaf spring and support strip, and 
correlate with the channel gap (spacing of the plates). 
The strain gage was selected for the smallest size 
practical: as thin as possible and yet of a standard 
type. Metal foils gaging 0.003 inch in thickness were 
selected. The gage is a temperature-compensated 
type with a 35041 resistance. The leaf spring is 
about 9/16 inch long. 
The basic Strain-gage instrumentation incorporates 
a Wheatstone bridge, an amplifier, and a two-channel 
strip-chart recorder. The gages are placed in two 
legs of the Wheatstone bridge, and the bridge is null-
balanced at the desired nominal dimension. Any 
change in the resistance of the gage unbalances the 
system and is detected as a change in voltage. 
The output from the probes is also permanently 
recorded on a strip chart. The speed of chart re-
corder and probe drive can be adjusted to a 1:1 
ratio of chart location to element location. 
Notes: 
1. This information may interest the aircraft, auto-
mobile, and tool industries. 
2. Inquiries may be directed to: 
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10343 
Source: V. M. Kolba and D. L. Vetter 
Reactor Engineering Division 
(ARG-10338)
(continued overleal) 
This document was prepared under the sponsorship of the Atomic	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per-	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000342 2020-03-16T18:12:26+00:00Z
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 0- 10343 Category 05


Design of a strain-gage probe

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