Microbend fiber optic strain gauge

• US 5,020,379 A
• Filed: 09/09/1987
• Issued: 06/04/1991
• Est. Priority Date: 10/30/1986
• Status: Expired due to Fees

• Current Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Berthold, John W., Reed, Stuart E.
• Primary Examiner(s): Raevis, Robert
• Application Number:
  US07/094,580
• Time in Patent Office: 1,364 Days
• Field of Search: 73/800, 73/766, 73/705, 73/708, 356/32, 356/33, 356/34, 350/96.1, 350/96.15, 350/96.16, 350/371, 250/227
• US Class Current: 73/800
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01L 1/245 using microbending

Abstract

A microbend strain gauge comprises a pair of plates having facing offset corrugations which clamp a signal optical fiber therebetween. The optical fiber is coated and a light signal is supplied to one end of the fiber which is read at an opposite end of the fiber by an optical sensor. Modulations in the light are primarily due to a difference in pressure being applied to the fiber by the plates. A second optical fiber, is subjected to the same thermal condition and its light signal compared to the light signal through the signal optical fiber to offset any temperature error introduced into the signal by changes in temperature. Aluminum, polyimide or gold coating increases temperature resistance for the fibers.

Claims

1. A strain gauge operable in hostile environments comprising:

a pair of plates made of a material having a temperature expansion coefficient dissimilar to that of a material to be tested for the purpose of increasing the range of the sensor and having facing and offsetting corrugated surfaces and wherein at least one plate is attached to the material to be tested;

a buffer coated first optical signal fiber clamped between the corrugations of the plates for being bent to a greater or lessor extent depending on pressure exerted on the plates for moving the plates together;

a buffer coated reference optical signal fiber located in the vicinity of the plates so as to be simultaneously exposed to the same thermal and other conditions along its length as the first optical fiber;

optical signal applying means including a light source and light splitting means connected to one end of each optical fiber for simultaneously applying an optical signal to both optical fibers; and

optical detector means connected to the opposite ends of both optical fibers for measuring the modulations in the optical signal transmitted through the first optical fiber which modulations correspond to pressures applied to the plates and for reading the modulations in the optical signal transmitted through the reference optical fiber.

2. A strain gauge according to claim 1, wherein said signal and reference fibers have a glass core and cladding and an aluminum coating.

3. A strain gauge according to claim 1, wherein said signal and reference fibers have a glass core and cladding and a polyimide coating.

4. A strain gauge according to claim 1, wherein said signal and reference fibers have a core of SiO₂, and a coating of gold.