The Foxboro Company

David N DeMoura

Howard W Nudd

Mohan Prasad

A method for adaptively scheduling maintenance of a sensor ( ) infers the need for maintenance of that sensor on the basis of an error signal indicative of a difference between a measurement signal generated by that sensor and an independently obtained reference signal that is correlated with the measurement signal ( ). Although the reference signal is not identical to the measurement signal, the correlation between these two signals assures that when the sensor is functioning, the two signal will track each other over time. The method includes the step of generating this error signal and then monitoring that error signal to detect a triggering event indicative of a mismatch between the reference signal and the measurement signal. This mismatch is indicative of a probability that there exists a malfunction in the sensor. The value of this probability depends on the choice of the triggering event.

Statistical trend generator for predictive instrument maintenance

A differential-pressure instrument the body of which forms a sealed interior pressure chamber containing a fill-liquid and includes a pair of flexible diaphragms to apply to the fill-liquid an input differential pressure to be sensed by an IC strain-gauge chip within the chamber. A spring plate divides the interior pressure chamber into two sections and is deflectable in response to differential pressures. Overrange pressure protection is provided by a valve which is closable by an elastomeric pad carried by the spring plate when the plate deflection reaches a pre-set amount. Valve closure locks the fill-liquid in place alongside the plate to provide an incompressible liquid back-up preventing further deflection of the plate, thus preventing further increases in differential pressure across the IC chip. In one embodiment, valves are placed on both sides of the spring plate to protect against both high-side and low-side overrange pressures. In another embodiment, a washer is secured to the spring plate to provide a relatively high spring-rate for deflection in the high-side direction, so that the instrument can more readily be employed for measuring high-span differential pressures.

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Taunton, MA, United States of America

David N DeMoura