Fiber optic sensing device

Rotary regenerative heat exchange apparatus having a rotor including a central rotor post and a concentric rotor shell spaced therefrom to provide an annular space therebetween, a mass of heat absorbent material carried in the annular space between the rotor post and the rotor shell, a housing surrounding the rotor in spaced relation including inlet and outlet ducts at opposite ends for a heating fluid and for a fluid to be heated, bearing means adapted to support the rotor for rotation about its axis, means for rotating the rotor about its axis, means supporting the inboard end of the sector plate, actuating means at the outboard end of the sector plate adapted to drive the sector plate vertically into a sealing relationship with the adjacent edge of the rotor, said actuating means including a transmitter of infrared rays, fiber optic cable means connected to said transmitter including a transmitting end and a receiving end separated by a gap that brackets an end edge of the rotor, a receiver for infrared rays connected to the receiving end of the cable, and motor means responsive to a beam of infrared rays projected across said gap adapted to drive the sector plate into a sealing relationship with an adjacent end of said rotor.