Measuring and testing – Volume or rate of flow – System
Patent
1977-08-08
1979-02-06
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
System
G01F 158
Patent
active
041377664
ABSTRACT:
A magnetic flowmeter includes a field coil extending along the longitudinal axis of a flow conduit for generating an integral magnetic field concentrically located about the coil and perpendicular to the flow. An inner electrode surrounds the coil, and the conduit itself is used as the other electrode, thereby providing a large surface-area electrode for sensing flow induced voltages. High current (over 20 amperes), very short duration (less than 10 millisecond) pulses energize the field coil whose inductance is low enough to permit electrode output voltages to be read within a few milliseconds after the magnetic field current pulse is turned on. The measured output voltage comprises a short-pulse, flow induced component proportional to flow rate, superimposed on a d-c voltage approximately equal to the galvanic potential at the electrodes. In a preferred embodiment, a pulse transformer, connected between the sensing electrodes and the readout circuitry, passes the flow induced component, while at the same time isolating the d-c component, thereby producing at its output a signal representing the actual flow signal. In an alternate embodiment, two voltage readings are sampled, one when the magnetic field is at steady-state on value, the other after the field current is turned off. Since these two readings are within milliseconds of one another, they are simply subtracted to produce the actual flow signal without having to compensate for any drift in the galvanic d-c voltages.
REFERENCES:
patent: 3902366 (1975-09-01), Gruner
patent: 3965738 (1976-06-01), Watanabe
patent: 4010644 (1977-03-01), Bonfig et al.
P. C. Eastman et al., "A Magnetic Flowmeter with Concentric Electrodes", Instrumentation Technology, Jun. 1970, pp. 52-55.
Karnakis Andrew T.
Ruehl Charles A.
The Foxboro Company
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