Fischer & Porter Company

Roy F Schmoock

Herbert A Shauger, Jr

Elmer D Mannherz

John S Yard

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. And because current flow through the electromagnets is heavy during the pulse intervals, the resultant peak magnetic flux is high, thereby enhancing the signal-to-noise ratio of the flowmeter.

Low duty cycle electromagnetic flowmeter

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 to flow rate. The magnetic field is created by a pair of pole pieces formed of 'hard' magnetic material. The pieces are placed at diametrically-opposed positions and are magnetically interconnected to define a magnetic circuit. Excitation pulses which alternate in polarity are periodically applied by respective magnet drivers to coils wound about the pole pieces to alternately magnetize the pieces in one direction and remagnetize the pieces in the reverse direction, thereby establishing the desired field. The duty cycle of the pulses is such as to reduce the average power requirements to a very low level. In order to operate the flowmeter from a standard 50 or 60 Hz power line, the line voltage is divided by an odd integer to permit the magnet drivers to be alternately triggered on the peak positive and peak negative crests of the power line voltage.

Electromagnetic flowmeter with alternating permanent magnet field

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.

Electromagnetic flowmeter with triangular flux drive

An electromagnetic flowmeter for metering the flow rates of fluids of low conductivity, the flowmeter including a non-magnetic spool within which is disposed a pair of electrode assemblies at diametrically-opposed positions embedded with an insulating layer molded against the inner surface of the spool. Each assembly is constituted by a curved measuring electrode plate and a curved shielding electrode plate concentric with the spool, the face of the measuring electrode plate being exposed. Received within the insulating layer and covering the faces of the measuring electrode plates is a tubular liner made of dielectric material whose properties are appropriate to the fluid being metered, the liner defining a flow conduit for the fluid. In operation, each measuring electrode forms one plate of a capacitor whose dielectric is the liner and whose other plate is the fluid being metered, the electrodes acting as a capacitance-sensor to detect the voltage induced in the fluid when it intercepts a magnetic field whose lines of flux are normal to the flow direction.

Capacitance-type electrode assemblies for electromagnetic flowmeter

A highly compact electromagnetic flowmeter unit interposable between the flanged ends of upstream and downstream line pipes for metering fluid passing through the line. The flowmeter is constituted by a cylindrical casing of ferromagnetic material within which a pair of electromagnet coils is supported at opposed positions along a diametrical axis normal to the longitudinal axis of the casing, the longitudinal axis passing through the central flow passage of an annular pressure vessel. The vessel, which is formed of high-strength insulating epoxy material, is molded within the casing and encapsulates the coils as well as a pair of pre-cast electrodes formed of conductive epoxy material disposed at diametrically-opposed positions with respect to the flow passage along a transverse axis at right angles to the coil axis to define a unitary structure. The epoxy of the electrodes is compatible with that of the vessel, whereby a fluid-impermeable bond is formed therebetween. The unit is compressible between the end flanges of the pipes by bridging bolts that pass through bore holes in the pressure vessel or lie outside the casing to encage the unit.

Unitary electromagnetic flowmeter having molded electrodes

A flangeless electromagnetic flowmeter unit interposable between the flanged ends of upstream and downstream line pipes for metering fluid passing through the line, the unit being encaged by bolts extending between the flanged pipe ends and being subjected to compression by these flanged ends to effect a fluid seal. The flowmeter is constituted by a non-magnetic spool of high strength to provide a flow conduit for the fluid. Surrounding the spool and concentric therewith is a cylindrical housing to define an annular inner chamber. Mounted at diametrically-opposed positions in the chamber along a coil axis normal to the longitudinal flow axis are electromagnetic coils, a strap joining these coils to define a magnetic circuit therewith. Electrodes are supported on the spool at diametrically-opposed positions along an electrode axis at right angles to the coil axis.

Flangeless electromagnetic flowmeter

A driver for the excitation coil in the electromagnet of an electromagnetic flowmeter, wherein the fluid to be metered is conducted through a flow tube to intersect the transverse magnetic flux field created by the electromagnet. The driver includes an a-c line rectifier whose output is coupled to the coil by a pair of switching transistors, the control electrodes of which are connected to the output of a comparator having first and second input terminals. Applied to the first terminal of the comparator is an alternating square wave voltage, each cycle of which has a positive and a negative gating pulse such that the transistors are alternately actuated, the arrangement being such that the rectified output is applied by the transistors to the coil with a polarity which is alternately reversed. The comparator includes a positive feedback loop connected between its output and the first terminal to produce a pulsatory output so that during each negative and positive gating interval, the coil is excited by a train of pulses whose duty cycle is varied in a manner regulating current flow through the coil to maintain a substantially constant current level.

Constant-current duty-cycle driver for electromagnetic flowmeter

A compact electromagnetic flowmeter unit interposable between the flanged ends of upstream and downstream line pipes for metering fluid passing through the line, the unit being subject to compression by the flanged pipe ends to effect a fluid seal. The flowmeter is constituted by a non-magnetic metal spool of high strength whose inner surface is protectively covered by an insulating liner to provide a flow conduit for the fluid. Surrounding the spool and concentric therewith is a cylindrical housing fabricated of ferromagnetic material, the housing being formed by complementary half-pieces which include end plates that join the corresponding ends of the spool to define an annular inner chamber. Mounted adjacent the inner surface of the half-pieces at diametrically-opposed positions along a coil axis normal to the longitudinal flow axis are relatively thin coils which are shaped to conform to this surface to define electromagnets. Electrodes are supported on the spool at diametrically-opposed positions along an electrode axis at right angles to the coil axis. The inner chamber is filled with a potting compound to seal in the electromagnets and the electrodes.

Unitary electromagnetic flowmeter with sealed coils

An electromagnetic flowmeter system in which the flow rate signal yielded by the flowmeter primary is applied as an input to a secondary which acts to measure the ratio of the input signal to a reference voltage proportional to the magnetic flux established in the primary, the reference voltage reflecting variations in this flux. Ratio measurement is effected in the secondary by means of a feedback loop in which the reference voltage is pulse-modulated by pulses having a constant width and a frequency which varies in accordance with the flow rate, the pulses having a duty cycle sufficient to cancel the input signal at the input of a summing amplifier. When the variable frequency pulse output from the secondary accurately represents the flow rate, the pulse-modulated reference voltage will then be equal in magnitude and opposite in phase to the input signal.

Electromagnetic flowmeter system having a feedback loop

An electromagnetic flowmeter which includes a pair of electrodes molded of electrically-conductive synthetic plastic material disposed at diametrically-opposed points in a flow tube through which the fluid being metered passes to intercept a magnetic field, thereby inducing a voltage in the electrodes that is a function of flow rate. The inner wall of the tube is protectively covered by an insulating liner molded of a synthetic plastic material having an affinity for the electrode material and fused to the periphery thereof to define a monolithic conduit which is leak-proof.

Electromagnetic flowmeter having a monolithic conduit

An electromagnetic flowmeter wherein a liquid to be metered is conducted through the flow tube of a primary to intersect a transverse magnetic field produced by an electromagnet. The resultant signal induced in the liquid is 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 that of the standard a-c power line. 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 flowmeter secondary includes a delayed automatic gain or smoothing network that is activated when a signal having excessive noise component is detected which persists for a predetermined period, activation serving to extend the response time of the secondary and thereby reduce the influence of the noise component thereon whereby the output of the secondary has a favorable signal-to-noise ratio.

Electromagnetic flowmeter having noise suppression network

A highly compact electromagnetic flowmeter unit interposable between the flanged ends of upstream and downstream line pipes for metering fluid passing through the line, the unit being subject to compression by these flanged ends to effect a fluid seal. The flowmeter is constituted by a non-magnetic metal spool of high strength whose inner surface is lined with insulating material to provide a flow conduit for the fluid to be metered, the spool also serving to withstand the compressive forces to which the unit is subjected as well as the fluid pressure. Surrounding the spool and concentric therewith is a cylindrical housing fabricated of ferromagnetic material, the housing being preferably formed by complementary half-pieces which are interconnected and include end plates which join the corresponding ends of the spool to define an inner chamber. Integral with the half-pieces are two magnet cores which extend at diametrically opposed positions along an axis normal to the longitudinal axis of the cylindrical housing, the cores being surrounded by coils to define electromagnets. Mounted on the spool at diametrically-opposed positions along a transverse axis at right angles to the core axis are two electrodes. The inner chamber is filled with a potting compound to encapsulate the electromagnets and the electrodes, the housing serving as a mold for this purpose.

Unitary electromagnetic flowmeter

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.

Harmonic noise suppression in electromagnetic flowmeter

A flangeless electromagnetic flowmeter insertable between upstream and downstream pipes which have the same internal diameter, the adjacent ends of said pipes having like flanges. The cylindrical body of the flowmeter is interposed between the flanged ends of the pipes, the body being provided with an annular pressure vessel formed of insulating material to define a central flow passage whose diameter matches the internal diameter of the pipe whereby the flowmeter functions to meter the flow rate of fluid passing through the pipes and the passage along a longitudinal axis extending therethrough. A pair of electromagnetic coils is embedded in the vessel at opposed positions with respect to the passage to establish a magnetic field therein whose lines of flux are substantially perpendicular to the longitudinal axis. Also embedded in the vessel is a pair of electrodes at opposed positions with respect to the passage, the electrodes lying along a transverse axis at right angles both to the lines of flux and the longitudinal axis. The flanged ends of the pipe are bridged by bolts to clamp the flowmeter body therebetween.

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Yardley, PA, United States of America

Roy F Schmoock