A precision capacitor sensor

Abstract

A precision, low cost, capacitor sensor comprised of two parallel plates, with an air dielectric, with preferably both substrates comprised of vitreous materials and electrically conductive coating, but with at least one of the substrates and coating being transparent. The coatings are preferably of identical material, thickness and pattern to offset stress distortion of the sensor plates from thermal expansion and contraction. Uniform spacing between the plates is provided by means of glass fibers of uniform diameter, dispersed in a matrix of adhesive and bonded under pressure, deposited between the plates as two thin semicircular seal rings surrounding the dielectric and separated by a diametrical gap, allowing entrance or escape of air dielectric. A novel feature, provided by at least one plate and coating being transparent, is use of optical measuring techniques during fabrication to verify acceptability of the manufacturing process and uniformity of the sensor product. This permits easy, rapid, efficient and economical grading and process control of the sensors during fabrication with resulting improved precision performance of the product and economical cost to manufacture. As an option, three or more of the four faces of the two substrates will bear conductive coatings, for structural stability, to minimize distortion in capacitance due to changes in temperature.