Long base inclinometer with optical measurement

Patent metadata

Field	Value
Publication number	US-9995579-B2
Application number	US-201314647791-A
Country	US
Kind code	B2
Filing date	Dec 2, 2013
Priority date	Nov 30, 2012
Publication date	Jun 12, 2018
Grant date	Jun 12, 2018

Abstract

A tiltmeter to measure a variation in inclination of a structure from a given starting position. The tiltmeter has two pots, each pot contains an identical volume and identical height of an identical liquid. A communication device connects the two pots and allows the liquid to flow between the two pots by the principle of communicating vessels. Two optical measuring devices are provided, one optical measuring device per pot. Each optical measuring device measures a variation in height of the level of liquid in the associated pot. The optical measuring devices are fiber optic devices coupled to a common light source.

First claim

The invention claimed is:

1. A tiltmeter to measure a tilt variation of a structure from a given starting position, comprising:
two sealed pots, each sealed pot comprising a closed high end and a low end, and each sealed pot containing an identical volume and an identical height of an identical first liquid, and an identical second liquid on top of the first liquid to prevent evaporation of the first liquid, the second liquid being less dense in volume than the first liquid;
a tube configured to connect the two sealed pots at one side of their low ends and to enable the liquid to flow between the two pots in accordance with a principle of communicating vessels, the tube being distinct from the two sealed pots to constitute a separate component of the tiltmeter;
two fiber optical interferometers, one fiber optical interferometer per sealed pot, each fiber optical interferometer measures a variation Δz in height of a liquid level of the liquid in the associated pot, each fiber optical interferometer comprises:
a light source, of central wavelength λ 0 , to generate a light beam toward the associated pot;
a reflecting surface positioned in a volume of the second liquid inside the associated pot;
an optical measuring fiber to transport and guide the light beam toward the associated pot, a first end of the optical measuring fiber, fixed at a level of a high end of the associated pot and disposed facing the reflecting surface, forming with the reflecting surface an external Fabry-Pérot optical cavity;
a detector to detect an interferometric signal generated by interference between a reference light beam and a measurement light beam, the interferometric signal comprises information on a movement of the liquid level relative to the first end of the optical measuring fiber, the reference light beam corresponds to a fraction of the light beam from the light source reflected by the first end of the optical measuring fiber, and the measurement light beam corresponds to a fraction of the light beam from the light source reflected by the reflecting surface and following an optical path in the Fabry-Pérot optical cavity, variation of the liquid level relative to the first end of the optical measuring fiber is a function of the liquid level height variation in the associated pot; and

wherein the fiber optical interferometers are coupled to a common light source.

2. The tiltmeter as claimed in claim 1 , wherein the fiber optical interferometers are extrinsic fiber optic devices and the light source is common to the two fiber optical interferometers; and the tiltmeter further comprises 1*2 channel coupler to split the light beam from the common light source into two light beams.

3. The tiltmeter as claimed in claim 2 , wherein the first end of each optical measuring fiber is inside the associated pot.

4. A measuring system comprising the tiltmeter as claimed in claim 1 ; and further comprising a device to determine a tilt variation of the structure in accordance with values measured by the fiber optical interferometers.

5. The measuring system as claimed in claim 4 is configured to measure geophysical deformations.

6. The tiltmeter as claimed in claim 1 , wherein the first liquid is water and the second liquid is silicone oil.

7. The tiltmeter as claimed in claim 1 , wherein a number of the sealed pots is greater than 2 and a number of fiber optical interferometers equals the number of the sealed pots; and further comprising a plurality of tubes, each tube connecting a different pair of sealed pots.

8. The tiltmeter as claimed in claim 1 , wherein said each sealed pot is made from a non-oxidizable material.

9. The tiltmeter as claimed in claim 1 , wherein a distance between the two sealed pots is between 10 m to 1 km.

10. The tiltmeter as claimed in claim 1 , wherein a distance between the two sealed pots is at least 30 m.

11. The tiltmeter as claimed in claim 1 , wherein each pot includes at its low end, a lower face placeable in contact with a surface of a bore to couple the tiltmeter to said bore when said tiltmeter is introduced into said bore.

Assignees

• Centre Nat Rech Scient
• Univ Montpellier
• Centre Nat Rech Scient

Inventors

• Boudin Frederick

Classifications

• G01C9/22

  with interconnected containers in fixed relation to each other · CPC title

• G01C9/06 Primary

  Electric or photoelectric indication or reading means · CPC title

• G01C2009/066

  optical · CPC title

• G01B11/26

  for measuring angles or tapers; for testing the alignment of axes · CPC title

• G01C5/04 Primary

  Hydrostatic levelling, i.e. by flexibly interconnected liquid containers at separated points · CPC title