Showing papers on "Magnetic circuit published in 1968"

Magnetic equivalent circuits

Abstract: The possibilities of using magnetic, instead of electric, equivalent circuits for eddy-current devices, which have recently been pointed out by Laithwaite, are here explored further. Couplings between distributed flux paths and windings can be expressed in terms of a generalised linkage parameter N, which is associated with flux linkage in electric circuits, and with an analogous current linkage in the magnetic equivalent. The magnetic-circuit treatment extends to rotating, as well as to static, devices, and leads to a view of induction machines as nonpassive magnetic elements. The relationships between the energy flow through the terminals, the mechanical forces and the magnetic terminal parameters are examined, and an alternative equivalent circuit, in which the analogue of current is not the flux but its rate of change, is shown to be in many respects a more useful one. The force equations are applicable, in particular, to devices in which induced currents are important.

Unbalanced magnetic pull in a 6-pole induction motor

Abstract: A 6-pole 10kW induction motor has been specially constructed for a comprehensive series of steady-state and transient measurements of the magnitude of unbalanced magnetic pull resulting from an eccentric air gap. These measurements have shown that unbalanced magnetic pull is critically dependent on Saturation of the magnetic circuit, and that the magnitude in the cage-rotor motor is much less than in the wound-rotor motor. Comparisons between measurements and calculations show that most existing theories inaccurately predict the magnitude of transient unbalanced magnetic pull during starting, the effect of slotting and saturation, the effect of a cage rotor, and the action of load currents. A simple theory is developed which gives reasonable agreement with measurements for the wound-rotor motor over a range of supply voltages about the rated value.

Starting performance of synchronous motors with solid salient poles

Abstract: The asynchronous performance of a synchronous motor, at a given slip, may be estimated from the 2-axis operational-admittance frequency functions Yd(jsω0), Yq(jsω0). The functions are commonly depicted as frequency-response loci. The frequency-response loci of a laminated-pole motor are shown to be analogous to the traditional induction-motor circle diagram. An accurate theoretical method is given to determine the asynchronous performance from the 2-axis loci, allowing for the effect of armature resistance. In addition, an approximate graphical method is given for the simplified condition when armature resistance is neglected.New equivalent circuits for the solid-pole motor are derived. The new circuits allow for the distribution of flux entering the rotor surface, and for the possibility of complete pole-tip saturation. Impedances, representing the parts of the magnetic circuit containing solid iron, are based on the rectangular magnetisation characteristic, and therefore have a magnitude, determined by the voltage across them, and a constant angle of 26.6°. The impedances are inserted into the equivalent circuits and the operational admittances are calculated by an iterative method. It is shown that the angle of the single effective ‘solid iron’ rotor impedance is found to lie between 26.6° and 45°, depending on the rotor frequency and flux. The method is also applicable to machines in which adjacent pole shoes are connected by end rings.Comparisons are shown between calculated and measured operational-admittance loci and between calculated and measured starting-performance characteristics for the solid-salient-pole micromachine at Imperial College, London, and for ten large solid-salient-pole machines of widely different dimensions and numbers of poles.A method of measuring, without attenuation, the component of oscillating starting torque of a synchronous motor, by measuring the total instantaneous input power, is demonstrated.

Multichannel magnetic head with common leg

Abstract: A read-write head assembly incorporates multiple transducing elements in an integral ferromagnetic structure, all elements being jointed to a common ferromagnetic leg to complete the magnetic circuit. The common leg serves as an air bearing slider for noncontact recording.

Review of Circuit Approach to Calculate Shielding Effectiveness

Abstract: The shielding effectiveness of an enclosure at low frequencies can be readily computed using a circuit approach. Not only does this technique include the effects of the properties of the shield material, but it also includes the details of the geometry of the enclosure. Furthermore, this approach allows a nonempirical consideration of mesh enclosures and the effects of resistive seams in enclosure walls. By working with the circuit analogue, penetration by transient fields can also be computed. Essentially the enclosure is viewed as an antenna. In the case of magnetic shielding effectiveness, the enclosure is viewed as a short circuited loop antenna. In the case of electric field penetration, the enclosure is viewed as a fat electric dipole. Using this characterization and exact solutions where available, the current distribution on the outside of the enclosure is first determined. Then, based on the current distribution, the penetrating fields are computed. The equations are developed in such a way as to preserve a lumped circuit analogue for the low-frequency region. The basic circuit equations for magnetic field penetration are rederived from a rigorous solution. Rules to estimate the rise-time, fall-time, and peak magnitudes of transient penetrating fields are developed. The electric shielding effectiveness is developed in a similar manner. In both cases the results of the circuit approach agree well with those based on rigorous solutions of the electromagnetic boundary conditions. The results also agree with published experimental data on both large and small enclosures.

Some aspects of electrical machines with open magnetic circuits

Abstract: Every electrical machine consists of electric and magnetic circuits interlinked. Good machines have circuits of low resistance and reluctance, the latter generally achieved by the use of a steel structure. If magnetic flux is made to thread a relatively long air path, compensation for the higher reluctance otherwise introduced can be sought by making the area of the flux path large. The paper shows how useful shapes of machine can be developed in which a large part or all of the magnetic circuit consists of air. Machines included are open-bar transformers, single-sided linear induction motors, and homopolar d.c. machines with superconducting field windings. Vertical forces in open-sided linear motors are calculated. The paper concludes with a brief discussion of the possibilities of electromagnetic current collection for traction systems employing a moving transformer

Vehicles with linear induction motors

Abstract: 1,194,438. Vehicles propelled by linear electric motors; air cushion vehicles. MERLIN GERIN. 11 Nov., 1968 [17 Nov., 1967], No. 53265/68. Headings B7K and B7L. [Also in Divisions H1 and H2] Auxiliary electrical power for heating, lighting, or producing air cushions for lifting and guiding, of a vehicle 18, Fig. 1 (or 28, Fig. 2), propelled along a rail 10 (or 24) by a linear electric induction motor which comprises induction coils 14 and 16 (or 26) in the rail and an armature comprising windings (not shown) and magnetic circuit closure members 20 and 20 1 (or 30) on the vehicle, is supplied to the vehicle from the travelling field produced by the induction coils 14 and 16 (or 26), by providing at least one pick-up coil 22 (or 32) on the armature members 20 and 20 1 (or 30) so that a varying electromotive force is induced in the coil 22 (or 32) which is dependent for its magnitude on the degree of asynchronism between the travelling wave and vehicle; rectifiers and storage batteries are provided to compensate for these variations in the auxiliary power supply.

The Application of the Direct Current Comparator to a Seven-Decade Potentiometer

Abstract: The design and construction of a self-balancing direct current comparator for use in a seven-decade potentiometer is described The comparator generates an output current whose value, as a proportion of a constant input current, is determined to a very high accuracy by the ratio of the numbers of turns of two windings on a magnetic core A linear, adjustable voltage scale is obtained by passing this output current through a resistor whose value does not vary with current Since the voltage adjustment is made by varying turns on a magnetic core and not by means of a resistive divider, the usual problems of contact resistance and thermal electromotive forces associated with this adjustment in conventional potentiometers are avoided The main sources of error in the comparator and the design techniques used to keep the errors less than the smallest step of the output current are discussed A self-checking feature whereby the linearity of each step of the output current can be checked quickly and easily is described The performance of the prototype model is given The normal range of the potentiometer is from zero to 2 volts in steps of 01?V

Electronic timepiece construction employing a flat step-by-step electromechanical energy converter

Abstract: There is disclosed herein an electrical timepiece including electronic circuitry for generating timing pulses, an electromechanical energy converter driven in stepwise fashion by the timing pulses and a mechanical movement having a second hand driven directly by the energy converter and gear train also driven by the energy converter to drive indirectly the hour and minute hands. The electromechanical energy converter disclosed is characterized by a wound stator having a plurality of magnetic circuits separately excitable to complete a magnetic path with a rotor. As the magnetic circuits are energized in succession, the rotor is attracted from one magnetic circuit to the next, producing stepwise rotation in synchronism with the excitation. A particular feature of the energy converter is the fact that its axial dimension is substantially less than its radial dimension, resulting in a flat configuration especially useful in a wrist watch.

Pulse-responsive stepping motor

Abstract: 1,161,613. Electric motors. W. KOHLHAGEN. 5 Sept., 1966, No. 39603/66. Heading H2A. A stepping motor has two sets of stator polepieces 16, 18 mounted with permanent magnet 28 and wound core 20 on a frame 26 and rotor 14 mounted on core 20 so that two magnetic circuits are formed with core 20 common to both. Rotor 14 is provided with equally spaced peripheral poles 46 co-operating with poles 22, 24 on stators 16, 18 respectively. Under the influence of the permanent magnet flux the rotor poles are aligned with poles 24 on stator 18 to provide a rest position. If coil 44 is energized the induced magnetic polarity of rotor 14 is changed and poles 46 are simultaneously attracted into alignment with poles 22 of stator 16 and repelled by poles 24 on stator 18. On de-energization of the coil, the rotor poles are attracted by poles 24 to complete the step. To ensure that rotor 14 rotates in one direction with constant torque the peripheral length of the stator polepieces reduces in the direction of rotation such that the polepieces at the extreme end of each set have the same width as the rotor polepieces. Other configurations may be used to give different torque characteristics, Figs. 8 and 9 (not shown). The rotor mounting may be modified to provide an annular air gap with the core, Fig. 7 (not shown). In the alternative construction, Figs. 10 and 11 (not shown), poles (314) of upper field plate (312) alternate with poles (318) of lower field plate (302) around rotor (290) and an annular magnet (296) is secured between the field plates. Rotor 296 is mounted on shaft (310) journalled in core (304) which carries a winding (294). In operation, energization of coil (294) causes rotor poles (316) to be attracted to poles (318) and, on subsequent de-energization the rotor poles are attracted to poles (314) (as shown in Fig. 11), the direction of rotation being ensured by rotor pole extension (330). In a modification, where the number of rotor poles is equal to the number of poles on one field plate, the width of the rotor poles varies to provide the correct direction of rotation and graded torque over the step, Fig. 14 (not shown).

Ferroresonant amplifying servomotors

Abstract: A ferroresonant servomotor characterized by the fact that saturation coils are series connected with diodes and the resulting circuits are in parallel connection and are connected to an alternating current supply voltage, the diodes, which are connected in series with the saturation coils through which passes flux produced by primary coils of the same ferroresonant circuit, being connected in an inverse conduction sense, while control coils proper, through which passes direct current, are mounted on each pole in such a way that their ampere-turns are added in the closed magnetic circuit of the pole to the ampereturns of the saturation coils on the poles of one of the ferroresonant circuits and are subtracted from the ampere-turns of the saturation coils at the poles of the other ferroresonant circuit.

Long-wavelength response of magnetic reproducing heads

Abstract: The distribution of the long-wavelength magnetic flux in unshielded and shielded magnetic head cores is described and calculated. Two effects are found, depending on the path of the flux: the "secondary gap effect" and the "undulation effect." The secondary gap effect causes an increasing output level at long wavelengths; it occurs because of the finite permeability of the core. The undulation effect causes undulation in the reproducing-head wavelength response; it depends primarily on the dimensions of the core in the neighborhood of the tape. Experimental measurements confirm the validity of the calculations quite well.

Magnetic head assembly with sidebar

Abstract: A magnetic head assembly, useful for noncontact magnetic recording, is formed to provide an inner cavity, wherein a thin magnetic core is fixed against a cavity wall. A magnetic sidebar, to which electrical coils are mounted, is secured adjacent to the core to complete the magnetic circuit.

Pole piece saturation in magnetic electron lenses.

Abstract: A new method is described for determining the flux density distribution in magnetic electron lenses of finite permeability. The method involves a simple modification to the resistance network analogue of the magnetic circuit. Pole piece flux densities have been determined under normal and saturation conditions in a high power objective lens. The influence of pole piece saturation on the axial field distribution is discussed.

A Square-Loop Magnetic Core Model for Computer-Aided Circuit Transient Analysis

Abstract: Square-loop magnetic core models presently used by automated circuit-analysis computer programs are inadequate. Instead, the effect of MMF F on flux ? is described by a more appropriate nonlinear core model, ? = ??(F,F) + ?i(F,?), based on the elastic and inelastic ? components. The core parameters may be measured or derived from a manufacturer catalog. The model has been incorporated into the automated computer-program TRAC (Transient Radiation Analysis by Computer), which was subsequently applied to transient analyses of several magnetic circuits. Machine-computed voltage and current waveforms agree satisfactorily with experimental oscillograms.

Linear electric drive with windingless carriage means at least partially embracing conductive rail means

Abstract: A RAIL CARRIAGE IS PROPELLED BY THE REACTION BETWEEN A MAGNETIC CIRCUIT CARRIED BY THE CARRIAGE AND WHICH HAS A GAP THE MAGNETIC CIRCUIT BEING ENERGIZED FROM AN AC CURRENT CARRYING CONDUCTOR AND A CONDUCTOR RAIL LYING IN THE GAP. THE REACTION MAY BE PRODUCED BY A GAP OF VARYING DIMENSIONS, BY SHADED-POLES OR BY A TWO-PHASE SUPPLY.

Transducer with variable permeability magnetic member

Abstract: 1,209,107. Measuring force electricallv. GENERAL ELECTRIC CO. Nov. 28, 1968 [Jan. 3, 1968], No. 56623/68. Heading G1N. Apparatus for measuring force comprises a magnetostrictive member 16, Fig. 3, in a closed magnetic path energized by a magnet 12 and incorporating a Hall plate element 18. A second similar magnetic circuit including magnet 12a and magnetostrictive member 16a balances the flux in the Hall plate element 18 when the forces on members 16, 16a are equal.

The thickness measurement of thin fluid films by a magnetic reluctance technique

Abstract: The design, construction and operation of a transducer for measuring the thickness of very thin fluid films is described. The transducer utilizes the principle of varying the reluctance of a magnetic circuit and is capable of measuring film thicknesses of the order of 1 μm with a resolution of 0·05 μm.

Shaded poles in unusual electric motors

Abstract: Modern machine theory has been developed to deal with motors and generators of cylindrical shape in which the conductors of both rotor and stator are contained in slots, and in which the airgap is an extremely small part of the magnetic circuit. As a result, the prediction of the performance of devices in which a large part of the magnetic path is through air is extremely difficult, but an imaginative use of the shaded-pole principle can be used to indicate, at least qualitatively, what will happen.

Residue arithmetic using balanced magnetic circuits

Abstract: Residue arithmetic and digital balanced magnetic circuits have been separate objects of research in the last ten years. This paper points out certain potentially interesting areas for them to be considered together. Following a review, the concept for a residue arithmetic unit capable of forming sums and products at the same time is described. A small balanced magnetic residue arithmetic unit was designed and built, and it displayed satisfactory margins and stability.

The acceleration magnetic field of a steady-current loop

Abstract: Centripetal acceleration in a current loop results in an azimuthal, inverse-square magnetic field--with no counterpart from differentially separated, opposite magnetic poles. A result, large on the atomic scale of dimensions, is a torque that rotates such moments to be collinear with an applied field, i.e., space quantization.

Direct-current transformer having a single common magnetic circuit

Abstract: A DEVICE FOR TRANSFORMING DIRECT CURRENT COMPRISES A SINGLE MAGNETIC CIRCUIT WHICH HAS A VARIABLE MAGNETIC FIELD IN WHICH THE GALVONOMAGNETIC RESISTANCE MEMBERS OF A BRIDGE NETWORK ARE LOCATED. THE MAGNETIC CIRCUIT HAS WINDING MEANS FOR PROVIDING THE CONTROLLING FIELD EXCITATION IN DEPENDENCE UPON THE DIRECT CURRENT TO BE TRANSFORMED. A DIRECT-CURRENT AMPLIFIER HAS ITS INPUT CONNECTED TO THE BRIDGE NETWORK AND HAS ITS OUTPUT CIRCUIT IN NEGATIVE FEEDBACK CONNECTION WITH THE WINDING MEANS TO PROVIDE THE MAGNETIC CIRCUIT WITH FEEDBACK EXCITATION OPPOSED TO THE CONTROLLING EXCITATION. THE MAGNETIC CIRCUIT IS AT LEAST IN PART MAGNETICALLY SATURABLE AT MAGNITUDES OF THE FEEDBACK EXCITATION ABOVE PREDETERMINED LIMIT VALUE.

Magnetic Cored Coil Structure

Abstract: 1,187,738. Transformers and inductors. STANDARD TELEPHONES & CABLES Ltd. 14 Nov., 1968, No. 53992/68. Heading H1T. A magnetic cored coil structure includes two magnetic core members 1, 2 which provide a primary magnetic circuit and define a winding space 15 in which a coil (not shown) is positioned on at least member 1 (e.g. on a central hollow boss 3); and terminals 17 secured by insulating material 18 to member 1. The surface of the core member on which the coil is wound is coated with insulation 16. A tubular magnetic adjuster slug 9 is fastened to a self-tapping screw 8 which engages an insulating plastics nut 11 and has a head which is surrounded by an insulating head 10 which provides frictional engagement with the wall of a central bore 6 in the member 2. (An adjuster assembly of this kind is described in Specification 1,090,028.) The slug 9 may be moved longitudinally in the bores 6 and 4 in order to adjust the reluctance of the air gap 7 between members 1 and 2. The magnetic core members may be made of ferrimagnetic material (e.g. ferrite) or of compound powders of iron or nickel-iron alloys. A method of assembling the structure is disclosed. The insulating material may be epoxy resin filled for increased strength or colour coding; and the terminals may extend out of the moulding for insertion into a printed circuit board.

The application of multistable magnetic cores for dialing purposes in telephony

Abstract: Multistable magnetic cores have the well-known property that a certain amount of flux, stored in the core, remains unchanged for a long time. This amount of flux can be broken down by feeding a number of voltage pulses, with a constant volt-second integral and the right polarity, to a core winding. Each of these readout pulses will lower the flux level in the core until there is no flux left, and from that moment a readout pulse only causes a small reversible change in flux, setting up a very short induction EMF in the core windings. A simple integrating network can be used to judge the output voltage of a winding, and it gives no output if the former results from a reversible flux change. If the pulse generator has a repetition frequence of ten cycles per second, the output pulses of the integrating network, after being shaped by a monostable trigger, will be suitable for dialing purposes in conventional telephone systems. A predetermined amount of flux, corresponding to one of the numbers one to ten, can easily be obtained by discharging a loaded condenser in series with a resistance through a core winding.

High‐Efficiency Superconducting Homopolar dc Generators

Abstract: The immediate requirement for flux pumps appears to be a design capable of producing 104 A at 100 W and high efficiency to energize large stabilized magnets. We have, however, successfully operated homopolar superconducting dc generators and also stabilized solenoids in helium vapor rather than liquid, and it appears reasonable to suggest that large magnets could be energized during the latter stages of cooldown, so that the power requirements for reasonable energization times may be less than this. Two designs for homopolar superconducting dc generators will be discussed and their performances reported on; both use permanent magnet and iron rotors. The first design has produced 1600 A and 20 W. The most significant feature of the design is the magnetic circuit used to generate in excess of 6 kG in the normal spot crossing the sheet. This enables reasonable power to be generated in a low‐speed (300 rpm) design. There are, however, large losses attributed to sloshing of liquid helium. The second design is ...

Electro-magnetic force motor

Abstract: 1,116,043. Electromagnets. DOWTY ELECTRICS Ltd. 7 July, 1965 [9 April, 1964], No. 14797/64. Heading H1P. An electromagnetic force motor comprises a solenoid 1 and an annular body 5 of resin mounted side-by-side on a non-magnetic, metallic guide tube 2, one or more electrical components (such as surge-damping rectifiers) being embedded in the resin body 5. As described, a magnetic circuit 8, 9, 11, 12 and plunger 14 are included, the plunger 14 being spring-coupled to a rod 15, actuating anhydraulic valve. The plunger 14 may be manually operated by a push-button 23 contained in a rubber boot 24.

A low inductance strip-line recording head

Abstract: A prototype high energy-efficiency recording head for use in a high packing density recording system has been developed. The operation of the head in the writing mode depends on the magnetic field round a thin strip conductor rather than flux leakage from the magnetic circuit as in a conventional ring-type head. The presence of ferrite in the vicinity of the strip increases the field produced for a given strip current. Since its low input impedance is unsuitable for direct connection to electronic circuits, it has been necessary to use an intermediate pulse transformer. By making this transformer an integral part of the recording head, a very compact unit is realizable. Care has been taken in the design of the structure to minimize any stray inductance which may be comparable to that of the head element. Advantages of the proposed head are its good high-frequency performance and suitability for high track densities.