| 摘要 |
<p>A speed sensor for sensing the rotational speed of an N bladed fan such as in a turbo-machine application includes a polarization-preserving optical circuit (20) positioned adjacent the locus described by the remote ends of the blades (B). First (S1,S2,S3,S4) and second (S5,S6,S7,S8) sets of sensing segments of the optical circuit (20) are spaced apart from one another by an angular spacing equal to that of the blades and with the first set of sensing segments angularly offset from the second set. The optical circuit has two orthogonal polarization modes, and the first sets are cross-coupled by a coupler (C) to transpose the polarization modes. The orthogonal polarization modes of optical energy launched into the optical circuit at an input (22) are subjected to phase shifts as the optical fibre is perturbed by pressure variations caused by the moving fan blades with the cumulative phase shift in each portion of the optical circuit subtracted as a consequence of the cross-coupling and the resulting light output at an output (24) having an intensity or other characteristics which varies as a function of the rotational speed of the fan.</p> |
