GB1575523A

GB1575523A - Strain gauge assemblies

Info

Publication number: GB1575523A
Application number: GB4521276A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1977-10-27
Filing date: 1977-10-27
Publication date: 1980-09-24

Description

(54) IMPROVEMENTS IN OR RELATING TO STRAIN GAUGE ASSEMBLIES (71) 1, SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to strain gauge assemblies and particularly, though not exclusviely, to assemblies for measuring linear displacement.

Where conventional strain gauges, such as the simple unbonded wire or foil resistance strain gauges are used to measure very small displacements, the change in resistance will be correspondingly low and will require large amplification for measurement purposes.

The present invention provides strain gauge assemblies which magnify displacements which are applied to the assembly.

According to the present invention a strain gauge assembly comprises an elastic sheet having an aperture therein and so shaped that the sheet buckles when opposite margins are moved apart, and a strain gauge connected to the sheet by means arranged to magnify strain in the sheet.

In a preferred embodiment of the invention the strain gauge is attached to the ends of arms outstanding from the sheet and peripherally spaced thereabout.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings accompanying the Provisional Specification by which: Figure 1 is a perspective view of a strain gauge assembly according to the invention.

Figure 2 is a plan view of an alternative form of the sheet forming part of the assembly shown in Figure 1.

Figure 3 is a perspective view of part of the assembly of Figure 1 when subject to a buckling load.

The strain gauge assembly shown in Figure 1 includes a generally rectangular flat sheet 1 of stainless steel 0.010 in thick having a rectangular aperture and a set of four upper arms 3a and four lower arms 3b, each of which are normal to the flat sheet and fastened to the sheet near the corners thereof. The upper arms 3a and the lower arms 3b support unbonded strain gauge wires 4a and 4b respectively near the outer ends of the arms. The sheet 1 has a pair of tabs 2a and 2b at opposite ends of the sheet for attachment to a body which is to be strained.

In operation, when the tabs 2a and 2b are urged apart in the directions A shown in Figure 1, sheet 1 deforms into the buckled configuration shown in Figure 3, and the distance between the outer ends of the arms 3a and 3b changes and hence the strain applied to the wires 4a and 4b changes. The arms serve to magnify the strain applied to the tabs, the wire strain gauge sensing the magnified strain.

A further increase in magnification of the applied strain can be obtained by modifying the shape of the sheet 1. Figure 2 shows a sheet 1 which is similar to that illustrated in Figure 1, but having cut-out portions 6 and 7 which increase the degree of buckling of the sheet for a given strain.

Forms of strain gauges other than unbonded wire strain gauges may be included in embodiments of the invention. For example, a strain gauge assembly in accordance with the invention may include a capacitance strain gauge attached to the sheet 1.

WHAT I CLAIM IS: 1. A strain gauge assembly comprising an elastic sheet having an aperture therein and so shaped that the sheet buckles when opposite margins are moved apart, and a strain gauge connected to the sheet by means arranged to magnify strain in the sheet.

2. A strain gauge assembly according to Claim 1 in which the sheet and the aperture therein are substantially rectangular.

3. A strain gauge assembly according to Claim 9 having a pair of tabs disposed at op

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. (54) IMPROVEMENTS IN OR RELATING TO STRAIN GAUGE ASSEMBLIES (71) 1, SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to strain gauge assemblies and particularly, though not exclusviely, to assemblies for measuring linear displacement. Where conventional strain gauges, such as the simple unbonded wire or foil resistance strain gauges are used to measure very small displacements, the change in resistance will be correspondingly low and will require large amplification for measurement purposes. The present invention provides strain gauge assemblies which magnify displacements which are applied to the assembly. According to the present invention a strain gauge assembly comprises an elastic sheet having an aperture therein and so shaped that the sheet buckles when opposite margins are moved apart, and a strain gauge connected to the sheet by means arranged to magnify strain in the sheet. In a preferred embodiment of the invention the strain gauge is attached to the ends of arms outstanding from the sheet and peripherally spaced thereabout. Embodiments of the invention will now be described, by way of example only, with reference to the drawings accompanying the Provisional Specification by which: Figure 1 is a perspective view of a strain gauge assembly according to the invention. Figure 2 is a plan view of an alternative form of the sheet forming part of the assembly shown in Figure 1. Figure 3 is a perspective view of part of the assembly of Figure 1 when subject to a buckling load. The strain gauge assembly shown in Figure 1 includes a generally rectangular flat sheet 1 of stainless steel 0.010 in thick having a rectangular aperture and a set of four upper arms 3a and four lower arms 3b, each of which are normal to the flat sheet and fastened to the sheet near the corners thereof. The upper arms 3a and the lower arms 3b support unbonded strain gauge wires 4a and 4b respectively near the outer ends of the arms. The sheet 1 has a pair of tabs 2a and 2b at opposite ends of the sheet for attachment to a body which is to be strained. In operation, when the tabs 2a and 2b are urged apart in the directions A shown in Figure 1, sheet 1 deforms into the buckled configuration shown in Figure 3, and the distance between the outer ends of the arms 3a and 3b changes and hence the strain applied to the wires 4a and 4b changes. The arms serve to magnify the strain applied to the tabs, the wire strain gauge sensing the magnified strain. A further increase in magnification of the applied strain can be obtained by modifying the shape of the sheet 1. Figure 2 shows a sheet 1 which is similar to that illustrated in Figure 1, but having cut-out portions 6 and 7 which increase the degree of buckling of the sheet for a given strain. Forms of strain gauges other than unbonded wire strain gauges may be included in embodiments of the invention. For example, a strain gauge assembly in accordance with the invention may include a capacitance strain gauge attached to the sheet 1. WHAT I CLAIM IS:

1. A strain gauge assembly comprising an elastic sheet having an aperture therein and so shaped that the sheet buckles when opposite margins are moved apart, and a strain gauge connected to the sheet by means arranged to magnify strain in the sheet.

3. A strain gauge assembly according to Claim 9 having a pair of tabs disposed at op posite margins of the sheet.

4. A strain gauge assembly according to Claim 3 in which cut-outs are formed at the corners of the aperture in the margins to which the tabs are attached.

5. A strain gauge assembly according to Claim 4 in which the cut-outs are substantially semi-circular.

6. A strain gauge assembly according to Claim 3, Claim 4 or Claim 5 in which cut-outs in are formed at the junctions of the tabs with the sheet.

7. A strain gauge assembly according to any previous Claim having arms outstanding from the sheet and peripherally spaced thereabout with the strain gauge attached to the arms at or near the ends thereof.

8. A strain gauge assembly according to Claim 7 having arms outstanding from both faces of the sheet and a separate strain gauge attached to the arms outstanding from each face of the sheet.

9. A strain gauge assembly substantially as herein described with reference to Figure 1 or Figure 2 of the drawings accompanying the Provisional Specification.