John J Yard

US Patent:

42274087, Oct 14, 1980

Filed:

Dec 7, 1978

Appl. No.:

5/967137

Inventors:

Roy F. Schmoock - Yardley PA
John S. Yard - Doylestown PA

Assignee:

Fischer & Porter Company - Warminster PA

International Classification:

G01F 160

US Classification:

7386117

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 field is transferred to a pair of electrodes mounted in the flow tube to yield a flow-induced signal. This field is established by an electromagnet supplied with excitation current through a periodically-operated switch to create a magnetic field which during each operating cycle is alternately turned on and off or reversed in flux direction at a predetermined drive frequency, as a consequence of which the signal includes undesirable noise components formed by even and odd harmonics of the drive frequency. To suppress such harmonic noise, the flow-induced signal is applied to a converter that includes a pair of synchronous demodulators operating in phase opposition and so synchronized with the periodically-operated switch that one demodulator passes its output to an integrator during the first half cycle of the drive frequency only in a gating interval in which the magnetic field is turned on and is at a constant flux level, and the other demodulator thereafter passes its output to the same integrator during the second half cycle only in a gating interval in which the magnetic field is turned off or is at a constant flux level in the reverse direction.