Low cost high precision sensor

Abstract

A universal sensor has a selectivity scaled condition responsive element such as a capacitive pressure transducer mounted on a common support with signal conditioning means embodied in an integrated circuit to provide a control signal precisely corresponding to a sensed condition. Electrically actuatable means on the support are incorporated in the circuit for low cost, mass producible calibration of the circuit and condition-responsive element relative to each other after assembly on the common support. Preferably, a capacitive pressure transducer and a reference capacitor are arranged in a charge-locked loop relation with a common node while an array of switches cycles the voltage across the transducer and reference capacitors with opposite transitions with a predetermined frequency so change in transducer capacitance results in a differential voltage at the common node. That voltage is amplified to drive a current source-sink-integrate network and adjust sensor output voltage to restore a balanced condition at the common node and maintain sensor output voltage at a level inversely proportional to transducer capacitance. The sensor is adapted for calibration to provide an electrical calibration signal for actuating calibration means such as electrically settable potentiometers, or serially programmed digital-to-analog converters or the like to provide bias and gain and non-linearity calibration in the sensor. In one embodiment, calibration is achieved by adjustment of variable capacitors.