Importance

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Abstract

A pressure sensor (10) that responds to stress introduced into a pair of cantilevered beams (42, 44), to sense pressures at two measurement points in a cassette (80). The pressure sensor includes a base (12) on which the cantilevered beams are mounted. The base also supports two S-shaped flat springs (34, 36) mounted in spaced-apart, parallel array. Pins (28, 29) supported by the S-shaped flat springs each contact a free end of a different one of the cantilevered beams. The pins transfer a force from an elastomeric membrane (86). This force is developed by fluid pressure acting on the elastomeric membrane in a fluid passage of a cassette used for pumping fluid. The pins transmit the force to the free ends of the cantilevered beams as an applied stress. Strain gauges (58, 60) that are fixed to the cantilevered beams each respond by producing a signal indicative of fluid pressure. This configuration senses a proximal and a distal fluid pressure in the cassette, with substantially zero displacement of the elastomeric membrane, thereby minimizing errors that would otherwise arise due to variations in the stiffness of the elastomeric membrane with displacement and providing a short response time to changes in pressure.

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First Claim