Development Of A 3-Plates Capacitive Pressure Sensor

This paper describes a micro capacitive pressure sensor for hydrostatic tank gauging (HTG), an emerging way to accurately gauge liquid inventory and to monitor transfers in tank farms. Since industrial storage vessels are huge, the sensing element must be sufficiently thick to withstand the large pressure inside the tanks. However, a thick diaphragm is insensitive to the relatively small pressure changes brought about by variations in the fluid head. To detect small pressure changes in the presence of a high constant load, a novel three-plates structure that introduces an additional plate between the two electrodes of a parallel plate capacitive pressure is proposed. A boss ring etched below the thick top plate, which serves as the sensing element, will come into contact with the middle pate and cause it to deflect when the applied pressure crosses a pre-determined threshold. Pressure is measured by monitoring the change in capacitance between the middle plate and the insulated substrate. As the middle pl...