Fiberoptic clearance detection method and optical fiber probe used therein

Abstract

A method includes transmitting light through at least one transmission optical fiber towards a target, receiving light reflected from the target through at least one signal optical fiber, filtering the received light at least two different wavelengths, and using the filtered light to detect a clearance variation. An optical fiber probe includes a plurality of optical fibers, a moisture-resistant enclosure enclosing the optical fibers, a hydrophobic layer situated over an end of the optical fiber probe for preventing moisture from reaching the optical fibers, and a broadband transmission layer between ends of the optical fibers and the hydrophobic layer.

1 . A method comprising:
 transmitting light through at least one transmission optical fiber towards a target;   receiving light reflected from the target through at least one signal optical fiber;   filtering the received light at least two different wavelengths; and   using the filtered light to detect a clearance variation.   
     
     
         2 . The method of  claim 1 , wherein the at least one signal optical fiber comprises at least three signal optical fibers and wherein filtering the received light at at least two different wavelengths comprises filtering at least three different wavelengths. 
     
     
         3 . The method of  claim 2 , wherein using the filtered light to detect a clearance variation comprises determining a variation estimate at each of the at least three different wavelengths. 
     
     
         4 . The method of  claim 3 , wherein using the filtered light to detect a clearance variation comprises comparing the variation estimates. 
     
     
         5 . The method of  claim 1  wherein transmitting light through the at least one optical fiber towards a target comprises transmitting light at least two different wavelengths. 
     
     
         6 . The method of  claim 1 , wherein using the filtered light to detect a clearance variation comprises converting the filtered light to a signal using at least one photodetector. 
     
     
         7 . The method of  claim 6 , further comprising using the signal for steam turbine operation control. 
     
     
         8 . A method comprising:
 transmitting light through at least two optical fiber probes towards a target with a first one of the optical fiber probes situated at a different distance from the target than a second one of the optical fiber probes;   receiving light reflected from the target through the at least two optical fiber probes; and   determining a clearance variation using a differentiation between the light received from the at least two optical fiber probes.   
     
     
         9 . The method of  claim 8 , wherein transmitting light through each optical fiber probe comprises transmitting light at least three different transmission wavelengths. 
     
     
         10 . The method of  claim 9 , further comprising filtering the received light at least three different filter wavelengths prior to determining the clearance variation. 
     
     
         11 . The method of  claim 9 , wherein determining the clearance variation comprises determining a variation estimate at each of the at least three different filter wavelengths of each optical fiber probe. 
     
     
         12 . The method of  claim 11 , wherein detecting the clearance variation comprises comparing the variation estimates. 
     
     
         13 . The method of  claim 8 , further comprising situating the first one of the optical fiber probes at a front working point and the second one of the optical fiber probes at a rear working point while transmitting the light towards the target. 
     
     
         14 . An optical fiber probe, comprising:
 a plurality of optical fibers and a moisture-resistant enclosure enclosing the optical fibers;   a hydrophobic layer situated over an end of the optical fiber probe for preventing moisture from reaching the optical fibers; and   a broadband transmission layer between ends of the optical fibers and the hydrophobic layer.   
     
     
         15 . The probe of  claim 14 , wherein the hydrophobic layer comprises a plate comprising sapphire. 
     
     
         16 . The probe of  claim 14 , wherein the hydrophobic layer comprises a coating comprising aluminum oxide.