SYMMETRICAL DIFFERENTIAL CAPACITIVE PRESSURE SENSOR

Differential capacitive sensors are common to pressure gauges. Previou s sensors of the bridge type have utilized only two variable (active) components, resulting in a half-bridge electrical equivalent circuit. There are numerous advantages of a symmetric full bridge, using four a ctive components. The symmetry improves linearity and increases signal to noise ratio, especially when supported by electronics based on syn chronous detection. Another advantage of symmetry is invariance to sca ling, through immunity to stray capacitance. This feature is especiall y important in relationship to the current trend toward micro-electro- mechanical systems. A crude, inexpensive, macroscopic prototype of the present design was built with attention to high sensitivity. Construc ted with a thin aluminized Mylar diaphragm, this device can readily re solve pressure changes smaller than 10(-2) Pa.