Abstract: An electromagnetic flowmeter in which the fluid being metered is conducted through a flow tube having a pair of electrodes, the fluid intersecting a magnetic field whereby the resultant voltage induced in the fluid is transferred to the electrodes to provide a signal indicative of flow rate. The magnetic field is created by a pair of electromagnets at diametrically-opposed positions on the flow tube to produce lines of magnetic flux thereacross. These electromagnets are driven by a low-frequency pulsatory wave, each periodic cycle of which is constituted by an excitation pulse of brief duration and high amplitude followed by a relaxation interval of relatively long duration so that the resultant duty cycle is low. Because the average power consumed by the electromagnets is at a very low level, this makes it possible to power the flowmeter from a remote station through a two-wire transmission line which also conveys the signal to the station.

Abstract: An electromagnetic flowmeter in which the fluid being metered passes through a flow tube to intersect the lines of flux of a magnetic field produced by an electromagnet whereby the resultant voltage induced in the fluid is transferred to a pair of electrodes mounted at diametrically-opposed positions on the tube. The electromagnet is so driven as to produce a flux field having a triangular wave form. The voltage signal yielded by the electrodes is therefore a composite having a triangular wave component that is a replica of the flux wave and a rectangular wave component that is generated by a spurious loop pick up voltage. The composite signal is applied to a converter and processed therein to cancel out the rectangular wave component whereby the converter output signal is accurately proportional to the flow rate of the fluid.

Abstract: A technique for stabilizing an insulating liner formed of thermoplastic material which is injection molded onto the inner surface of a metal spool having a cylindrical body provided with end flanges, an annular gap being created between the liner and the spool body due to differential shrinkage between the liner and the body as the molded liner cools and solidifies. In order to fill this gap to prevent a change in the inner diameter of the liner when the liner is subjected to the pressure of a fluid flowing therethrough, the spool body is provided with ports which extend between the exterior and interior surfaces thereof. These ports are sealed during the injection-molding process by removable plugs. After injection-molding, the plugs are removed and a thermosetting resin is introduced into one of the ports until the gap is filled as evidenced by the fact that the resin begins to rise in the other ports, the resin then being cured to solidify the filler.

Abstract: An apparatus for injection-molding an insulating liner onto the surface of a metal spool to be included in an electromagnetic flowmeter in which the fluid to be metered is conducted through the lined spool. The spool is composed of a cylindrical body having end flanges and a pair of diametrically-opposed circular bosses disposed midway between the flanges to receive the meter electrodes. To carry out injection molding, the spool is supported within a mold which defines a liner cavity conforming to the inner surface of the cylindrical body and to the faces of the end flanges, the liner cavity communicating with cavities conforming to the inner surface of the electrode bosses. The molding material is injected into a sprue in the mold which runs along the longitudinal axis of the spool toward the hub of a runner extending radially toward an axisymmetric ring gate opening into the liner cavity at a point adjacent the boss cavities.

Abstract: An electromagnetic flowmeter wherein a liquid to be metered is conducted through a flow tube to intersect a transverse magnetic field produced by an electromagnet, the resultant signal induced in the liquid being transferred to a pair of electrodes mounted at diametrically-opposed points on the tube. To avoid spurious signal components arising from stray couplings between the electromagnet and the loop constituted by the electrodes and the liquid bridging the electrodes, the coil of the electromagnet is energized by a low-frequency wave whose frequency is well below the standard a-c power line frequency. And, to avoid noise components produced when the liquid being metered is a slurry containing solid particles which impinge on the surface of the electrodes, the electrodes are fabricated of or coated by a carbide metal or an alloy thereof whose metallurgical hardness is such as to substantially reduce the generation of such noise components.

Abstract: An electromagnetic flowmeter having a flow tube which is interposable in a normally less-than-full fluid line. A pair of arcuate electrodes are mounted in the flow tube at opposed positions therein to span a substantial portion of the total tube circumference, whereby they are operative with respect to fluid in the tube in a range extending from a level close to empty to a level close to full. Associated with the flow tube is an electromagnet that is excited by a periodically-interrupted direct current to establish a magnetic field in the tube which is intercepted by the fluid passing therethrough to induce a signal in the electrodes. This signal is sampled during the steady state intervals of the magnetic flux to provide an output free of zero-shift error and of interference voltages.