Capacitance pressure transducer and method of fabrication therefor

Abstract

A capacitance pressure transducer comprising two fused quartz cylinders concentrically aligned with and separated from one another so that a small gap is established therebetween. The capacitance of the transducer is determined by the size of the gap and the length of capacitor electrodes which are disposed within the gap. Changes in capacitance are measured by an external circuit which is connected to the electrodes. The electrodes are attached to respective opposing surfaces of the inner and outer cylinders and responsive to pressure induced changes in the size of the gap. The cylinders are connected together by means of a unique joint formed between respective first ends thereof, so that the inner disposed cylinder is adapted to be cantilevered from the joint and suspended within the outer cylinder. That is, the first ends of each cylinder are formed with an identical taper. The inner cylinder is located within the outer cylinder, such that the respective first ends thereof form a close or flush fit relative to one another. The joint to bond the first cylinder ends together is formed by a metal (e.g. titanium) hydride solder process. A fused quartz-to-fused quartz seal is formed by the steps of supplying a mixture of an indium alloy solder and titanium hydride to the first ends of the inner and outer cylinders and heating the cylinders in a vacuum chamber. The titanium hydride acts as a flux for promoting a continuous and reliable solder joint between the first cylinder ends.