Pressure-responsive apparatus

Abstract

A pressure transducer has a capsule having two chambers separated from one another by a diaphragm. The capsule is made entirely of a glass-ceramics material, such as, lithium alumino silicate. One of the chambers is sealed and has a lens with a curved surface adjacent the diaphragm such that, when the capsule is illuminated, a Newton's Rings pattern is produced by interference between light reflected from the surface of the lens and the diaphragm. Pressure is communicated to the other chamber so as to cause the diaphragm to be deflected into or out of the sealed chamber with a consequent shift in the interference pattern which is used to provide a measure of the pressure change. The capsule also has two further chambers which are identical to the first two chambers and which are both sealed. One of these further chambers is illuminated to produce a second interference pattern. The difference between any shift in the two patterns gives an indication of the pressure change that is independent of temperature change. The two interference patterns may be produced by light from the same source supplied to the capsule via fibre-optic cables, the light being reflected onto the capsule by a prism assembly mounted directly on the capsule. Similarly the interference patterns may be focussed by the prism assembly onto an array of the ends of fibre-optic cables used to supply light from the patterns to photocells.