DE2345266A1 - Magnetic induction measurement in radial magnetic field - generated by permanent magnet in rotation symmetric air gap of magnetic circuit - Google Patents

Abstract

The magnetic field is generated in a circular air gap of a dynamic electro-acoustic transducer. An equivalent magnetic circuit and guiding element for inserting and removing the permanent magnet under test are provided. A fixed measuring coil consisting of two windings, which are arranged on the boundary surfaces define the air gap of the equivalent magnetic circuit in an axial direction. The measuring coil is connected to an integrator. Both windings of the measuring coil in opposite sense of winding are connected in series. Both windings are wound in the ring grooves of a hollow, cylindrical winding form.

Description

Device for measuring magnetic induction in

a_radial_Magnetf eld ^ ^

The invention relates to a device for measuring the magnetic Induction in a radial magnetic field generated by a permanent magnet under test in a preferably rotationally symmetrical air gap of a magnetic circuit, in particular in the annular air gap of a dynamic electroacoustic one Converter, is generated.

Measurements of this kind are required in the manufacture of electro-mechanical or electro-acoustic components in order to to be able to classify the components in predetermined quality classes. A preferred field of application of the invention is hence the testing of magnets for the manufacture of electroacoustic transducers for telephony purposes. The classification of the equipped with the magnets acoustic transducer according to the magnetic induction generated by them in predetermined Groups is used to adjust the volume. For example, it is common to use electrodynamic earphones for Telephones divide the reception reference attenuation range into four To subdivide groups that cover a total of 0 np to -1.2 Np.

It is well known to measure the magnetic induction by means of a small coil which is attached to the relevant point of the magnetic field is introduced in such a way that its axis with the direction of the magnetic field lines coincides. This coil is connected to a flux meter and then moved to a range of deviating magnetic Induction, in particular brought into a range of induction zero. The law of induction then results in the

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magnetic induction prevailing at the measuring location.

The invention is based on the object of creating a measuring device by means of which magnetic induction can be measured in air gaps, in particular in air gaps of electrodynamic transducers in which the aforementioned There is no possibility of arranging a measuring coil at the location of the measurement due to the small dimensions of the air gaps given is.

Starting from a device of the type mentioned at the outset, this object is achieved in that an equivalent Replacement magnetic circuit representing a simulation of the magnetic circuit and guide means for insertion and removal of the permanent magnet to be tested are provided that also ortfecte relative to parts of the equivalent magnetic circuit Measuring coil is provided which has two windings which are axially attached to the air gap of the equivalent magnetic circuit Direction delimiting boundary surfaces are arranged and that this measuring coil is connected to an integrator. This device according to the invention is thus characterized from that the axis of the measuring coil does not have to point in the direction of the magnetic field to be measured, which is comparatively small air gaps would require extremely small dimensions of the measuring coil. By the device according to the invention Rather, by a first winding of the measuring coil in the axial direction in the one boundary surface of the air gap forming part of the magnetic circuit and entering the magnetic flux by means of a further winding in the axial direction the magnetic flux emerging from the opposite boundary surface of the air gap was measured. By simple The radial flow can measure the difference between the two measured values will.

This difference formation can according to a development of the invention take place in a simple manner that the two windings of the measuring coil with opposite winding directions

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ORIGINAL INSPECTED

are connected in series, so form a differential probe.

According to another development of the invention, the structural design is characterized in that the two Windings in annular grooves of a hollow cylindrical bobbin are wrapped.

The integrator for determining the time integral of the voltage induced in the measuring coil, which is proportional to the magnetic flux is preferably formed by a ballistic galvanometer, in particular a light mark mirror galvanometer.

The natural oscillation of a ballistic galvanometer must be known to be large compared to the duration of the measurement process. They therefore have an extremely low restoring force, so that the return of the pointer or the light linear to the zero point takes a very long time after the measurement. It Obviously, the waiting times associated with this slow return will affect the speed at which measurements are taken can be carried out successively, greatly diminishes. It is an object of a development of the invention to this To eliminate disadvantage. This development is characterized in that in the zero point the swept by the light mark Scale path of the mirror galvanometer as well as symmetrical on both sides from this zero point in a mutual Distance which is smaller than the width of the light mark, photoelectronic components are arranged that the im Zero-point arranged photo-electronic component with a Switching amplifier is connected to switch off an auxiliary voltage returning the light mark to the zero point and that the photo-electronic ones arranged on both sides of the zero point Components are components of a balancing circuit that, when the photocurrent of the two photoelectronic Components generated a correction current for the drive coil of the mirror galvanometer. By such an arrangement is a very quick return of the light mark of the mirror gallery

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ORIGINAL INSPECTED

I ο f :: J 6 ο

vanometer in the zero position possible: after successful measurement a circuit is closed manually or automatically, in which the light mark of the galvanometer goes to its zero point is returned. As soon as the light mark reaches the zero point, the named auxiliary voltage is supplied by the Switching amplifier switched off. An (inevitable) overshoot of the light mark leads to the illumination of the corresponding one Photoelectronic component arranged at a distance from the zero point. This generates a photocurrent that drives the mirror galvanometer and thus the light mark in the opposite direction. A new overshoot of the Light mark in the opposite direction leads to an illumination of the second one arranged at a distance from the zero point photoelectronic component, which then generates a current that moves the light mark in the opposite direction. In this way, the light mark is "caught" in the zero point, i.e. a compensating current is fed to it until both are symmetrically arranged at a distance from the zero point photoelectronic components deliver the same photocurrent.

The device according to the invention is suitable for automatic Measurement and sorting of the magnets to be tested. The automatic sorting can according to a development of the Invention are effected in that along the swept by the light mark scale path of the mirror galvanometer photoelectronic Components are arranged that identify the tolerance ranges, i.e. the quality classes of the magnets to be tested and with an electrical evaluation circuit for automatic classification of the magnets to be tested in predetermined Tolerance ranges of magnetic induction are connected.

The above-mentioned guide means by means of which the magnet to be tested is introduced into or removed from the equivalent magnetic circuit this is removed, (whereby an induction voltage is generated in the measuring coil, the time integral of which is for

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the induction to be determined characterizing is ^c ä) ₉ ina summarize, according to a further development of the invention, are preferably provided with an operating handle, for example a lever linkage.

However, it is also possible to actuate the component carrying the magnet to be tested by means of an electrically controllable pneumatic drive device. The electrical control of this drive device is coordinated with the switching operations for performing the induction measurement zv / corner-wise via a computing circuit. In particular, it is advantageous to co-ordinate control with the involvement of a magnetizing coil that surrounds the spare magnetic circuit according to an embodiment of the invention and which is used for magnetization of the permanent magnet to be tested. The magnetizing coil is preferably fed by the aperiodic discharge current of a capacitor bank.

In the following, the invention is illustrated with reference to the drawing Embodiment explained in more detail:

Fig. 1 shows a section through an electroacoustic transducer for telephone purposes,

Fig. 2 shows a schematic representation of the invention Contraption,

FIG. 3 shows that used in the device of FIG Measuring probe,

FIG. 4 shows a circuit for the automatic return of the mirror galvanometer used for the measurement in FIG its zero position,

Fig. 5 shows the scale of the mirror galvanometer, which with photoelectronic components for automatic Zero point adjustment of the mirror galvanometer as well as for automatic sorting of the items to be checked Is equipped with magnets,

Finally, FIG. 6 shows a circuit diagram on the basis of which the magnetizing process of the magnets is explained target

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In Fig, 1 a known c-electrodynamic converter is shown; it has a permanent magnet 1, which is part of the magnetic circuit 2 for generating a radial magnetic field. The magnetic circuit comprises the yoke base 3> the yoke 2 and the pole disc 4. The yoke 2 and the pole disc 4 delimit an annular air gap in which the voice coil 5 ¹ attached to the transducer diaphragm is arranged. The magnetic induction generated by the magnet 1 in the annular air gap is decisive for the efficiency of the converter and thus for the volume that can be achieved. When manufacturing electroacoustic transducers of this type, there is therefore a need to measure the magnets used and to classify them into individual quality classes. The magnet 1 is a ring magnet. 1 shows individual values of the magnetic flux: 0 is the magnetic flux generated by the magnet 1 in the axial direction, 0 is the axial flux at the boundary between the pole disc 4 and the magnet 1, 0. is the leakage flux inside the magnetic circuit, 0 ^ ₀ is the

Sat

external leakage flux and 0 the radial flux in the annular Air gap which is decisive for the magnetic induction effective at the location of the voice coil 5 '.

In Fig. 2, a device for measuring the magnetic induction 0 and thus for measuring the air gap induction is shown schematically. The device comprises an equivalent ciagnetic circuit which is analogous to the magnetic circuit of the electrodynamic transducer shown in FIG. The equivalent magnetic circuit consists of a yoke base 3 '»the yoke 2' and the pole disc 4 ¹ . The pole disk 4 'and the yoke 2' delimit an annular air gap in which a measuring probe 5 is attached. The measuring probe 5 is shown in detail in FIG.

The device shown in Fig. 2 further comprises guide means 8, 9 »by means of which the replica of the yoke base 3 'can be introduced into the yoke 2'. The magnet to be tested 1 becomes pushed onto a mandrel 13 and held by this in a central position. The replica of the yoke base 3 'is on one

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Plate 11 attached, which is movable either by a lever linkage or by an electrically controllable pneumatic cylinder. The guide columns 9 are attached to a plate 10, which also serves as a fastening for the replica of the yoke 2 '. The replica of the yoke 2 ^f is enclosed by a magnetizing coil 12. This is used to magnetize the magnet 1 to be tested when it is inserted into the yoke simulation 2 ¹ . The leads of the measuring probe are connected to a mirror galvanometer (Fig. 4). The measuring probe 5 has two partial windings which are milled into annular grooves of a winding body preferably made of a non-magnetizable metal, for example brass. The distance between the two windings a corresponds to the thickness of the pole disc 4 or 4 ^! . The two partial windings 6 and 7 of the probe are wound in opposite directions. In order to avoid eddy current losses, the winding body is provided with a radial slot. This slot also serves to accommodate the supply lines for the two windings.

For testing, the magnet is placed on the mandrel 13 of the yoke base and pushed into the yoke with the aid of the guide means 8, 9. In the process, magnetic fluxes arise which are the same as the magnetic fluxes shown in FIG. 1. To measure these magnetic fluxes, the yoke base 3 'with the magnet 1 is removed from the yoke replica 2 ^! pulled out. An electrical voltage is induced in the partial windings 6 and 7 of the measuring probe 5. According to the law of induction, the time integral of this voltage is equal to the magnetic flux penetrating the relevant partial winding multiplied by the number of turns of this partial winding. As a result of the opposite winding directions of the two partial windings 6 and 7, a voltage appears on the leads of the measuring probe, the time integral of which is the difference between the two fluxes 0

^unc ^ 0OO is proportional. Since the two partial windings 6 and 7 are arranged on the two axial boundary surfaces of the annular air gap of the equivalent magnetic circuit, one of them measures the

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gnet 1 and pole disc 4 ^f passing flux 0_ and the other the leakage flux exiting from the pole disc in the axial direction 0, as a result of the opposite winding

SH

In the sense of the direction of the two partial windings 6 and 7, an induced voltage appears on the lead of the measuring probe, the time integral of which is the difference 0 «- 0 _e « = 0 ~ »s so the one sought Radial flow in the annular

fi δα Γ

gen air gap is proportional.

A mirror galvanometer with a very low natural frequency, a so-called ballistic galvanometer, is used as the integrator used. As is well known, the integration effect of such a ballistic glavanometer is based on its comparison for measuring duration of large natural oscillation duration.

The long period of natural oscillation, which is necessary for the determination of the time integral of the induction voltage is known to bring the practical handling The disadvantage is that the return of the light mark to the zero point, which is required after each measurement, is extremely time-consuming is. In the embodiment of the invention described above, the one shown in FIG Circuit arrangement for automatic light mark return and zero point adjustment of the mirror galvanometer used. This circuit works in the following way

In the idle state, the mirror galvanometer 20 is via the setting resistor 22 and the switch button 21 are connected to the measuring probe 5. The switch key 21 serves as a delete key. she is pressed after taking a measurement. As a result, the mirror galyanometer 20 breathes with an auxiliary voltage in connection that returns the light mark 23 (Fig. 5) to the zero point. As soon as the light mark 23 is in the zero point of Illuminated photo element arranged on the scale path 17 of the mirror galvanometer 20, this generates a control voltage for the switching amplifier 28. The switching amplifier 28 opens

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the contact 27 »of the mirror galvanometer in the auxiliary straws 20 is inserted so that -jir-d olas ©? Circuit interrupted. The auxiliary voltage 25 can be set by means of the potentiometer 24. The effective partial voltage is so ' set that there is an optimal return speed. Both sides of the zero point of the scale path 17 and symmetrically two photo elements 15 and 16 are arranged to it. They are arranged so that their effective surfaces too equal parts are illuminated by the light mark 23 when this is exactly in the zero point. A shift the light mark 23 from the exact zero position thus has a different intensity of illumination of the two photo elements 15 and 16 result, so that the photocurrent emitted by these has different values. The two photo elements 15 and 16 are electrically connected to each other (Fig. 4), so if the lighting is unequal, a resultant Voltage is generated which is fed to the mirror galvanometer and which moves the light mark in a direction in which this resulting walk becomes smaller .. Because of this optoelectrical Negative coupling v / the light mark is "caught" in the zero point. If when pressing the delete key 21 the The light mark does not appear in the zero point, this is due to the fact that it is for some reason beyond of the zero point, i.e. to the left of the zero point in FIG. 5. By actuating the pole reversal switch 26, it is through the auxiliary voltage 25 is controlled back to the zero point of the scale path and then with the help of the two photo elements 15 and 16 "caught" in the zero point. The potentiometer 29 serves to balance the two photo elements 15 and 16.

The magnet 1 attached to the replica 3 'of the yoke base is magnetized when the equivalent magnetic circuit is closed. The magnetization coil 12, which simulates the 2 ^! of the yoke. In order to magnetize the magnets in the saturation region, a field strength is required, which is large compared with the coercive

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feldstärke "The demand vii two high magnetizing current is battery-won as the discharge of a capacitor." It is important to ensure that the discharge of the capacitor bank erfo3gt aperiodic _s ie that the magnetization coil does not change 12 by current flowing during the operation sign. Based on the in 6, the magnetization is briefly explained: the capacitance of the capacitor bank has the value C, the inductance of the magnetization coil 12 is L, r is the ohmic resistance effective in the discharge circuit.

If the "capacitor C" is charged to the voltage ü * _C q at the time t = 0, this results from the application of the rule of meshes

L di / dt + ri + u _c = 0 (i = C du _c / dt) with the solution approach u => Up ₀ e ^
the characteristic equation
p ² + ρ r / L + 1 / LC β 0.
The solutions are

t _{n 2} = - r / (2L) + ~ \ j r ² / (2L) ² - 1 / LC.

The aperiodic limit case sought for optimal magnetization arises when

r ² / (2L) ² = 1 / LC.

This results in the ohmic resistance r:

r = 2 "γ L / C".

The measuring device described can be used as an automatic

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expand table measuring device. As a driving means for the closing of the substitute magnetic circuit can - wi® already mentioned - with compressed air operated pneumatic © means used will. The sorting of the test items Ia predetermined Quality classes, (those of a prescribed Eapindicfckeiteitgabe can be automated by adding further photo elements, e.g. photo elements 18 and 19 in PIg, 5 are arranged. These Fiio to elements supply the control voltage for further switching amplifiers, with the help of which the measures required for sorting the test items are controlled can be.

It is also possible to supply the ■ to be checked Automate magnets. For this purpose, for example, the equivalent magnetic circuit can be designed in a U-shape * so that the magnets are fed in and out in a cylindrical plate can. The operating point of the replacement magnetic circuit must be due to the geometric dimensions of the U-shaped "profile again be designed so that it is an equivalent replica of the original magnetic circuit of the electrodynamic transducer.

10 claims
6 figures

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Claims (10)

Device for measuring the magnetic induction in a radial magnetic field, which is generated by a permanent magnet to be tested in a preferably rotationally symmetrical air gap of a magnetic circuit, in particular in the annular air gap of a dynamic electroacoustic transducer, characterized in that an equivalent replica of said magnetic circuit (1, 2, 3, 4, Fig. 1) representative magnetic circuit (1, 2 ¹ , 3 ', 4 ^f , Fig. 2) as well as guide means (8, 9) for inserting and removing the permanent magnet (1) to be tested in this or from this substitute magnetic circuit (1, 2 ·, 3 ^f , 4 ¹ ) are provided that a ^{measuring coil (5) which is stationary relative to parts (2 f} , 4 ^f ) of the substitute magnetic circuit and has two windings (6, 7) is provided , which are arranged aii the boundary surfaces delimiting the air gap of the equivalent magnetic circuit in the axial direction and that this measuring coil (5) is connected to an integrator (20, FIG. 4). 2. Apparatus according to claim 1, characterized in that the two windings (6, 7) of the Measuring coil (5) with opposite winding directions are connected in series with one another (Fig. 3). -3. Device according to claim 1 or 2, characterized in that the two windings (6, 7) are wound in annular grooves of a hollow cylindrical bobbin (5) (Fig. 3). 4. Device according to «Ines of the preceding claims, there characterized in that the integrator tor a ballistic galvanometer, in particular one Lichtmarken-Spiegelgalvanoaeter (20) is. TPA 9/610/0202 - 13 - 509815/0025 5. Apparatus according to claim 4, characterized in that the zero point of the light mark (23) coated scale track (17) of the mirror galvanometer (20) and on both sides symmetrically from this zero point at a mutual distance that is smaller than the width of the light mark (23) »photoelectronic components (14, 15, 16) are arranged that the photoelectronic component (14) arranged at the zero point with a switching amplifier (28) for switching off an auxiliary voltage which returns the light mark (23) to the zero point (25) is connected and that the photoelectronic components arranged on both sides of the zero point (15, 16) are components of a balancing circuit (15, 16, 29) which, when the photocurrent of the two photoelectronic Components (15, 16) a correction current for the drive coil of the mirror galvanometer (20) generated. 6. Apparatus according to claim 4 or 5, characterized that along the swept by the light mark (23) scale path of the mirror galvanometer photoelectronic components (18, 19) are arranged with an electrical evaluation circuit for the automatic classification of the magnets to be tested (1) in predetermined tolerance ranges of the magnetic ones Induction connected. 7. Device according to one or more of the preceding claims, characterized in that that the guide means a preferably provided with an operating handle lever linkage for driving the the component (1'1) carrying the magnet (1) to be tested. 8. The device according to one or more of claims 1 to 6, characterized in that the Guide means an electrically controllable pneumatic VPA 9/610/0202 _{50981 5/0026} -14- Drive device for driving the component (11) carrying the magnet (1) to be tested. 9. Device according to one or more of the preceding claims, characterized in that the equivalent ^{magnetic circuit (1, 2 1} , 3 '»4') is enclosed by a magnetizing coil (12) for magnetizing the magnet to be tested (1). 10. The device according to claim 9 »characterized in that the magnetizing coil (12) of the aperiodic discharge current in a capacitor battery (C, Fig. 6) is fed. VPA 9/610/0202 509815/0025 Blank page