Pressure isolated fiber optic torque sensor

Abstract

Fabry-Perot and Bragg grating optical measuring principles are combined with a torsional stress sensing mechanism that converts torque applied in one fluid environment to force exerted in a second environment to measure extreme environmental parameters such as pressure in a petroleum producing borehole.

1 . A torque measuring instrument comprising:
 means for converting a torsional strain about an axis to a spatial displacement across a sensor element substantially parallel with said axis;   means for determining a value of said displacement; and   means for relating the value of said displacement to a value of said strain.   
     
     
         2 . A torque measuring instrument as described by  claim 1  wherein a value of said special displacement is determined by optical means. 
     
     
         3 . A torque measuring instrument as described by  claim 2  wherein said means for determining a value of said displacement comprises a Fabry-Perot etalon. 
     
     
         4 . A torque measuring instrument as described by  claim 1  wherein said means for determining a value of said displacement comprises a capillary tube load cell. 
     
     
         5 . A torque measuring instrument as described by  claim 4  wherein optical fiber is fused to opposite ends of said capillary tube. 
     
     
         6 . A torque measuring instrument as described by  claim 1  wherein said means for determining the value of said displacement comprises a pair of light reflective surfaces, one is which is a partially reflective dichroic. 
     
     
         7 . A torque measuring instrument as described by  claim 1  wherein said means for converting torsional strain comprises a Bourdon tube spiraled about said axis. 
     
     
         8 . A torque measuring instrument as described by  claim 7  wherein a fluid pressure within said Bourdon tube is converted to said torsional strain, said torsional strain being corresponded to a value of said fluid pressure. 
     
     
         9 . A torque measuring instrument as described by  claim 1  wherein said means for converting torsional strain comprises a first element that is rotatively displaced in a first fluid environment by torsional stress imposed in a second fluid environment, said first element displacement being relative to a stationary second element positioned within said first fluid environment; a plurality of hat-section links, each having a crown panel supported by a pair of substantially equal length leg panels, a distal end of one leg panel respective to each pair being secured to said first element and a distal end of the other leg panel respective to said pair being secured to said second element; at least a pair of beam elements diametrically traversing said first element through said axis, each of said beam elements supported at substantially opposite distal ends by the crown panels of respective pairs of hat-section links. 
     
     
         10 . A torque measuring instrument as described by  claim 9  wherein a first of said beam elements overlies a second of said pair proximate of said axis with a spatial separation distance there between. 
     
     
         11 . A torque measuring instrument as described by  claim 10  wherein means for determining a value of said displacement comprises means for determining a change in said separation distance between said beams. 
     
     
         12 . A torque measuring instrument as described by  claim 11  comprising optical means for determining a change in said spatial separation distance between said beams. 
     
     
         13 . A torque measuring instrument as described by  claim 12  wherein said optical means comprises a substantially reflecting first surface being disposed on said first beam and a dichroic second surface disposed on said second beam, both of said surfaces being normally traversed by said axis. 
     
     
         14 . A torque measuring instrument as described by  claim 13  wherein a collimated fiber optic light ray is directed along said axis, through said second surface and reflected from said first surface. 
     
     
         15 . A torque measuring instrument as described by  claim 12  wherein said means for determining a change in said separation distance between said beams comprises a capillary tube load cell disposed between said beams. 
     
     
         16 . A torque measuring instrument as described by  claim 15  wherein optical fiber is fused to opposite ends of said capillary tube. 
     
     
         17 . A torque measuring instrument as described by  claim 16  wherein independent fibers are axially aligned and fused to said capillary tube ends with an end separation distance between respective fiber ends. 
     
     
         18 . A torque measuring instrument as described by  claim 1  wherein said means for converting torsional strain comprises a Bourdon tube spiraled about said axis. 
     
     
         19 . A torque measuring instrument as described by  claim 18  wherein a fluid pressure within said Bourdon tube is converted to said torsional strain, said torsional strain being corresponded to a value of said fluid pressure. 
     
     
         20 . A torque measuring instrument comprising:
 means for converting a torsional stress about an axis to a lineal stress across a sensor element substantially parallel with said axis;   means for determining a value of said lineal stress; and   means for relating the value of said lineal stress to a value of said torsional stress.   
     
     
         21 . A torque measuring instrument as described by  claim 20  wherein said means for determining a value of said lineal stress comprises a Bragg grating optical fiber. 
     
     
         22 . A torque measuring instrument as described by  claim 20  wherein said means for determining a value of said lineal stress comprises a resonating beam. 
     
     
         23 . A torque measuring instrument as described by  claim 20  wherein said means for determining a value of said lineal stress comprises a capillary tube load cell. 
     
     
         24 . A torque measuring instrument as described by  claim 23  wherein independent fibers are axially aligned and fused to said capillary tube ends with an end separation distance between respective fiber ends. 
     
     
         25 . A torque measuring instrument as described by  claim 23  wherein a Bragg grating is written into a unitary fiber between said opposite capillary tube ends. 
     
     
         26 . A torque measuring instrument as described by  claim 20  wherein said means for converting torsional stress comprises a Bourdon tube spiraled about said axis. 
     
     
         27 . A torque measuring instrument as described by  claim 23  wherein a fluid pressure within said Bourdon tube is converted to said torsional stress, said torsional stress being corresponded to a value of said fluid pressure. 
     
     
         28 . A torque measuring instrument as described by  claim 20  wherein said means for converting torsional stress comprises a first element that is rotatively displaced in a first fluid environment by torsional stress imposed in a second fluid environment, said first element displacement being relative to a stationary second element positioned within said first fluid environment; a plurality of hat-section links, each having a crown panel supported by a pair of substantially equal length leg panels, a distal end of one leg panel respective to each pair being secured to said first element and a distal end of the other leg panel respective to said pair being secured to said second element; at least a pair of beam elements diametrically traversing said first element through said axis, each of said beam elements supported at substantially opposite distal ends by the crown panels of respective pairs of hat-section links. 
     
     
         29 . A torque measuring instrument as described by  claim 28  wherein a capillary tube load cell is disposed between said beams. 
     
     
         30 . A torque measuring instrument as described by  claim 29  wherein optical fiber is fused to opposite ends of said capillary tube. 
     
     
         31 . A torque measuring instrument as described by  claim 30  wherein a Bragg grating is written into a unitary fiber between said opposite capillary tube ends. 
     
     
         32 . A method of measuring torque comprising the steps of:
 converting a torsional strain about an axis to a spatial displacement across a sensor element substantially parallel with said axis;   determining a value of said displacement, and,   relating the value of said displacement to a value of said strain.   
     
     
         33 . A method of measuring torque as described by  claim 32  comprising the step of optically determining the value of said displacement. 
     
     
         34 . A method of measuring torque as described by  claim 33  wherein a Fabry-Perot etalon optically determines the value of said displacement. 
     
     
         35 . A method of measuring torque as described by  claim 33  wherein a Bragg grating written onto an optical fiber is used to optically determine the value of said displacement. 
     
     
         36 . A method of measuring torque as described by  claim 32  comprising the step of determining the value of said displacement by a evaluating a frequency change in a resonating beam that is distorted by said spatial displacement. 
     
     
         37 . A method of measuring torque as described by  claim 32  wherein said spatial displacement is transferred to a capillary tube load cell for determination of said displacement value. 
     
     
         38 . A method of measuring torque as described by  claim 37  wherein said torsional strain is induced by fluid pressure into a Bourdon tube wound about said axis.