Low pressure sensor

Abstract

Differentially connected capacitive sensors are mechanically coupled with the flexible capacitor plate of one sensor coupled to the source of pressure to be measured, the flexible capacitor plate of the other sensor coupled to ambient pressure. In a second embodiment, inaccuracies due to forces on the flexible plate are minimized by providing a housing with a tapered inner wall, an O-ring and a support to apply a radial load to the sensor due to clamping action from the tapered housing against the O-ring to provide a seal for the pressure sensing chamber. In a further embodiment, the cost of fabrication of the pressure transducer is minimized by providing the housing as a one piece cup. The electronics are mounted on the exterior surface of the low pressure side of the ceramic capacitor pressure sensing element and sealed in thereat by potting with an epoxy. In addition, an electrical pin connector from the electronics and a vent to the low pressure surface of the movable plate are secured in the potting material and extend externally thereof. In a further embodiment, pressures applied to the movable diaphragm of the pressure sensing element by the gasket are eliminated by providing a ceramic capacitor having a movable diaphragm element having smaller length and width dimensions than the fixed capacitor substrate. The gasket is positioned around the movable diaphragm element and on the fixed capacitor plate with the housing being stepped to apply a force against the gasket but remain out of contact with the movable diaphragm element.