Structural monitoring system

A monitoring system for detecting movement of a first part of a structure relative to a second part of said structure, said monitoring system comprising:

• (a) an interrogation source comprising:
• (1) a first light emitting element for emitting pulses of light;
• (2) a second light emitting element for emitting pulses of light which alternate with the pulses of light from said first light emitting element;
• and
• (3) a light detecting element;
• and
• (b) an optical encoder comprising:
• (1) a transmitter portion adapted to be connected to the first part of said structure, said transmitter portion having a first optical fiber connected to said first light emitting element, a second optical fiber connected to said second light emitting element and a third optical fiber connected to said light detecting element,each of said first, second and third optical fibers extending parallel to and abutting each of the other two of said first, second and third optical fibers, each of said first, second and third optical fibers having an end surface which lies in a first plane, each of said end surfaces occupying a position which differs lengthwise of said longitudinal axis from that of the others of said end surfaces within said plane;
• (2) a reflector portion adapted to be connected to the second part of said structure so that movement of said second part relative to said first part causes said reflector portion to move relative to said transmitter portion along a longitudinal axis, said reflector portion comprising a plurality of photo reflective surfaces facing said end surfaces and being spaced along said axis, said photo reflective surfaces lying in a second plane which is spaced from and parallel to said first plane so that the alternating pulses of light from said first and second light emitting elements are transmitted along said first and second optical fibers toward said photo reflective surfaces and pulses of light reflected from said photo reflective surfaces to the end surface of said third optical fiber are transmitted along said third optical fiber to said light detecting element, so that the direction of movement of the second part of said structure relative to the first part of said structure can be determined through the use of quadrature.