ADAPTIVE FILTERING OF PERIODIC NOISE

摘要

A noise cancelling system for a parameter measurement system (13) employing a delay line (15) to store a representation of the periodic noise being cancelled. The delay of the delay line is a multiple of the noise period, with timing circuitry (16) providing synchronization. The representation is continuously updated by adding the delay line output to the weighted output of the measurement system (13) in adder (14) and feeding the sum to the delay line input. Signals which are not synchronous with the reference signal (20) average out over time and do not accumulate in recirculating delay line (15). The delay line output (18) (or a function thereof) is fed to a transducer (17) that converts this signal to the same energy or signal type as measured by measurement system (13) such that the cancelling signal is applied in anti-phase to the input of the measurement system (13) as represented by the summing point (12).