Capacitance-change transducer applied to rotating vane anemometry and tachometry

Electrical transducing methods for use in rotating-vane anemometry and tachometry are discussed and the advantages to be gained from a capacitance-change pickoff are outlined. Both a theoretical and practical analysis for the capacitance variation in such systems is given, leading to the conclusion that the resulting change, when converted into a voltage-time signal is ideally suited to cable and telemetry transmission. A simple transducingcircuit technique is then presented with measured results indicating that changes of less than 0.01 pF can readily be resolved. In addition, the circuit performance with high residual-capacitance values is investigated, the results of which have led to the development of an insertion-type flowmeter. The paper is concluded by illustrating the application of the techniques in a respiratory-flow transducer.