Electromagnetic flowmeter system having automatically adjusted response

Abstract

An electromagnetic flowmeter in which fluid to be metered passes through a flow tube to intersect a magnetic field whereby the voltage induced in the fluid is transferred to a pair of electrodes mounted in the flow tube to yield a flow-induced signal having a random noise component. This field is established by an electromagnet supplied with an excitation current creating a magnetic field that is alternately turned 'on' and 'off' at a low frequency drive rate. The resultant flow-induced signal is sampled during each 'on' and 'off' field condition, successive differences therebetween serving to develop an analog output signal having a random noise content. To automatically adjust the output response time of the system as a function of the random noise content and thereby minimize the adverse effects of noise on the system, the analog output signal is fed to a statistical analyzer in which the signal is digitized before being supplied to a microcomputer programmed to determine the statistical significance of the difference between two arithmetic means. To this end, a first series of successive values of the digitized signal is used to establish the first mean and a first variance, and a second series of successive values to establish the second mean and a second variance. The computer, on the basis of the Student 't' statistic, calculates the difference between the two means to produce a digital output signal having the desired response time.