Bear Medical Systems, Inc.

Erik W Peterson

Henry L Burns

A gas flow measuring system employs an oscillating chopper valve alternately to deliver a flow head-generated pressure and a reference pressure to a pressure transducer. The chopper valve is driven by a stepping motor under the control of a microcomputer. The stepping motor drives the valve, with an oscillatory frequency determined by the microcomputer, between a first detented position, in which the flow head-generated pressure is delivered to the transducer, and a second detented position, in which the reference pressure is delivered to the transducer. The electrical signal produced by the transducer is fed to a sample-and-hold circuit, also under the control of the microcomputer, whereby the microcomputer controls the sampling rate of the sample-and-hold circuit. The microcomputer can thus establish an optimal sampling rate in accordance with the oscillatory frequency of the valve. In this manner, very fast sampling rates can be established, thereby minimizing the effects of zero drift in the transducer.

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Calistoga, CA, United States of America

Erik W Peterson