Signal conditioner for electromagnetic flowmeter

Abstract

A voltage to frequency converter or conditioner adapted for use with electromagnetic flowmeters produces a signal whose output frequency is related to measured flow while compensating for power frequency interference and variations in magnet current or magnetic induction B. The driving signal is summed with a feedback signal and coupled to a sampling integrator which drives the detector. The output of the detector (which may be integrated) is provided as the input to a VCO for producing the desired output signal. The VCO output is also coupled into a feedback circuit to which is also coupled a reference voltage which is at least proportional to the magnetic induction B or magnet current I. In one embodiment of the invention, an up/down counter is up counted using the VCO's output as a clock for a fixed time and is then down counted by a clocking signal related to power main's frequency. The time required for the down count operation is used to meter the feedback voltage to the summing junction at the input of the integrating sampler. This metering of the feedback voltage may be eliminated by the use of a multiplying DAC which produces an analog voltage corresponding to the product of the reference voltage and the count attained in the up/down counter which is modified so as to eliminate the necessity for down counting and is rather reset at the beginning of each integration period.