Fiber optic pressure detector

Claim 1

For use in apparatus for monitoring ambient pressure within a confined space, said apparatus including a light source, two light detectors, a source of fluid under pressure, control means for controlling the pressure of said fluid in accordance with the difference between the intensities of light sensed by said light detectors, and display means for displaying said pressure, a differential sensor unit comprising an envelope adapted to be placed within the confined space, said envelope having at least one wall movable in response to change in relative pressure between the interior and exterior of said envelope, a fluid conducting line in communication with the envelope interior and adapted to be connected to the fluid source, three light guides each having an internal end within said envelope, and of whose external ends, the first and second each face a light detector, and the third faces the light source, light-modulating mechanism mounted within said envelope in operative relation to the internal ends of said light guides to vary the light transmitted from the internal end of said third light guide to the internal ends of said first and second light guides and correspondingly to vary the intensity of light sensed by each of said light detectors, said light-modulating mechanism being relatively movable with respect to said internal ends responsive to movements of said movable wall, said internal ends and said light-modulating mechanism being so disposed and arranged that in a first position of said lightmodulating mechanism a majority of the light from the light source is transmitted from said third light guide through said first light guide to the first light detector, in a second position of said mechanism a majority of said light is transmitted through said second light guide to the second light detector, and in a third position equal amounts of said light are transmitted to the two light detectors, said light modulating mechanism being movable through a range of positions including said first, second and third positions. so that said control means acting through said pneumatic line will adjust the internal pressure in said envelope in accordance with the difference between the light intensities sensed by the detectors, whereby said internal pressure continually spans said ambient pressure and said display means continually displays said internal pressure.