Accelerometers
A fibre optic accelerometer particularly intended for use with an interferometer using the compliant cylinder approach but further providing a seismic mass at the core of the cylinder resulting in improved sensitivity and rejection of out-of-axis inputs.
1. A fibre optic accelerometer comprising a seismic mass coaxially constrained within a cylinder of compliant material, arranged to prevent the cylinder deforming inwardly under axial compression, the cylinder being circumferentially wound with optical fibre such that axial compression of the cylinder by the seismic mass increases stress in the optical fibre.
2. An accelerometer according to claim 1 , wherein the seismic mass includes a disc shaped portion.
3. An accelerometer according to claim 1 , wherein the seismic mass is secured by a tension member to a base plate.
4. An accelerometer according to claim 3 , wherein a spacer is provided between the cylinder and the base plate.
5. An accelerometer according to claim 4 , wherein the spacer is integral with the base plate.
6. An accelerometer according to claim 3 , wherein the base plate is integral with a platform or structure.
7. An accelerometer according to claim 1 , wherein the optical fibre is wound in a single layer.
8. An accelerometer according to claim 1 in which the seismic mass is coaxially constrained within first and second cylinders of compliant material, each cylinder being circumferentially wound with optical fibre.
9. An accelerometer according to claim 8 in which the seismic mass comprises a first circumferentially located bearer member arranged to bear on an end of at least one of the compliant cylinders.
10. An accelerometer according to claim 9 in which the first circumferentially located bearer member is arranged to bear on respective ends of both of the compliant cylinders.
11. An accelerometer according to claim 9 comprising a second circumferentially located bearer member arranged to bear on an end of a second of the compliant cylinders.
12. An optical interferometer comprising an accelerometer according to claim 1 .
13. A fibre optic accelerometer according to claim 1 , wherein said compliant material is rubber or rubber like.
14. A method of measuring acceleration comprising providing a seismic mass coaxially constrained within a cylinder of compliant material, the cylinder being circumferentially wound with optical fibre, axially displacing the seismic mass so as to compress the cylinder thereby increasing the stress induced in the optical fibre, and determining a stress value in the optical fibre.