DE2400193C3 - Method and circuit arrangement for demagnetizing a large-volume workpiece - Google Patents

Description

The invention relates to a method for demagnetizing a large-volume workpiece by means of a magnetic alternating field, the field strength of the magnetic alternating field by reducing the Magnetizing current and / or by increasing the distance between the workpiece and the magnetizing coil is reduced and the frequency of the alternating magnetic field is lower than that Grid frequency is.

As is well known, an alternating magnetic field penetrates the less deeply into a ferromagnetic body, the higher its frequency is. In order to achieve a sufficient penetration depth with large-volume bodies, Therefore, frequencies are required that are below the usual mains frequency.

A known method for demagnetizing large-volume workpieces therefore uses it as the magnetizing current a sinusoidal alternating current with a very low frequency of about 5 Hz. This known method has the disadvantage that demagnetizing coils, which are for the supply are designed with mains voltage and mains frequency, only with greatly reduced voltage or with strongly operate with reduced duty cycle.

In the known method, single armature converters serve as current sources for the demagnetization current of 5 Hz or corresponding motor-generators. These known low frequency power sources have the Disadvantages that they require a lot of material, space and weight and an ongoing In need of maintenance.

The invention is based on the object of specifying a degaussing method with the usual Degaussing coils, which are designed for continuous operation with mains voltage and mains frequency, under Maintaining the supply from the network are operable, but with regard to the demagnetization process the current flowing through the field-generating coil with a frequency compared to the mains frequency much lower frequency takes effect. In a further embodiment of the invention, a circuit arrangement is intended will be indicated by which such a demagnetizing current while maintaining the connection of the coil to the network is generated, and with which at the same time a demagnetizing current source is created, which is light and maintenance-free and which can be produced with little material expenditure leaves and takes up little space.

The invention solves this problem with the means characterized in claim I.

• i

A circuit arrangement for carrying out the method is characterized with that in claim 5 Means and measures implemented.

Expedient developments of the invention result from the subclaims 2 to 4 and 6 identified means and measures.

The invention is shown schematically in the drawing using a few exemplary embodiments. Here

Fig. 1 is a diagram of two during one period current pulse groups of different polarity occurring in a subharmonic oscillation sinusoidal intensity distribution within each pulse group as a function of time,

F i g. 2 shows a diagram of several current pulse groups according to FIG. 1 with slowly decreasing linearly Intensity of the strongest impulses in each impulse group,

F i g. 3 shows a diagram according to FIG. 2 with triangular shape intensity distribution and the same number of impulses within each impulse group,

4 shows a block diagram of a circuit arrangement for feeding a degaussing coil and

F i g. 5 shows a diagram of several voltages occurring in the circuit arrangement according to FIG. 4 in Dependence on the time.

In Fig. 1 shows over time / below a multitude of periods of a 50 Hz mains voltage and above two pulse groups / 1, h of alternating polarity that form a pulse or leakage current, which during two half-periods Tu, T: one comprising ten mains periods Tn, the period duration T having subharmonic oscillation occur, which forms the envelope curve 1 of the impulse or gap current. The pulse groups / 1 and h have a number of pulses that differs by one pulse, depending on the type of their intensity control.

Each of the two pulse groups / 1 and / 2 consists of five positive and six negative current pulses / u to / 15 or / 21 to / 2b, the intensity of which corresponds to the Envelope 1 first increases and then decreases.

In Fig. 2 are for the case in Fig. 1 in more detail shown sinusoidal envelope 1, and in Fig. 3 are for the case of a triangular Envelope 2 shows the amplitudes of the during several successive subharmonic oscillations occurring current pulses are shown. In both cases the amplitudes of the oscillation of the envelopes decrease 1 or 2 of the impulses slowly decrease monotonously according to the envelopes 3 and 4, respectively.

To generate the magnetization voltages described above, the method shown in FIG. 4 circuit arrangement shown. In this there is a degaussing coil 5 over two antiparallel! switched thyristors 6.7 at terminals 36, which can be connected to the feeding network. Between the cathode and the The ignition electrode of each thyristor 6, 7 is a resistor 8, 9 and the series connection of a rectifier 10, 11 and a secondary winding of an ignition transformer 12, 13 connected.

The primary winding of each ignition transformer 12,13 is at the output of a pulse amplifier 14,15, whose Input with the output of a first, short ignition pulses of constant duration emitting monostable Toggle circuit 16, 17 is connected, the input of which is connected to the output of a second, nachtriggerbarcn inonostable Toggle switch 18, 19 is located with controllable service life.

Fin limiter 20, which has a mains-frequency voltage applied to it at its input, is on the output side directly to the pulse input of a retriggerable flip-flop 18 and with the interposition an inverter 21 with the pulse input of the other retriggerable multivibrator 19 connected. The output of the limiter 20 is also connected to the input of one of a pulse frequency divider 22 with the division ratio 5: 1 and a pulse frequency plate 23 with the division ratio 2: 1 existing frequency divider connected. The one inputs of two integrators 24, 25 are each via a series resistor 26, 27; 28, 29 on the one hand with an output or with a negated output of the Frequency divider 23 and on the other hand connected to the output of a third integrator 30, the input of which Via a series resistor 31 with the help of a changeover switch 32 either with or with the reference potential a terminal 33 carrying the operating voltage can be connected. The other (negated) inputs of the two integrators 24, 25 are connected to taps of voltage dividers 34, 35 between the Reference potential and operating voltage are. A blocking input of the first flip-flop 17 is via a Switch 37 can be connected to reference potential.

The mode of operation of the circuit results from Fi g. 5, in which the essential voltage curves are shown.

From the 50 Hz sinusoidal voltage a present on the input side at the limiter 20, a 50 Hz square wave voltage b results on the output side upper output of the respective flip-flop 18 or 19 carries an L signal during its idle time.

The 50 Hz square wave voltage is also at the input of the frequency divider 22, 23, at one output of which a 5 Hz square wave voltage c occurs, which forms the input voltage of the integrator 24 and at the other output of which an inverse 5 Hz square wave voltage occurs which is on the integrator 25. The two triangular voltages d and c , which are phase-shifted by 180 ° with respect to one another, occur at the outputs of the integrators and are at the control inputs of the two retriggerable multivibrators 18 and 19, respectively. Their idle times therefore fluctuate depending on the instantaneous value of the triangular voltages c / or at the trigger time at the control input. e opposite.

The voltage swing and the DC voltage component of the two triangular voltages d and e are determined by a corresponding measurement on the one hand of the time constant and / or the charging current of the integrators 24 and 25 and on the other hand of the bias voltages for the inverting inputs of the operational amplifiers that can be tapped off by the potentiometers 34, 35 the integrators chosen so that the service lives of the two trigger circuits 18 and 19 fall below the period Tn of the mains frequency only during alternating half periods Ti and Ti , so that during each half period, for. B. Ts /, only one toggle switch, e.g. B. 18, falls back several times in its rest position and is then triggered again, while the other flip-flop, z. B. 19, remains in its unstable position because of its retriggering during the standing time exceeding the Neizperiodendauer Tn. Since the service life first increases and then decreases again, this results in the

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Outputs of the flip-flops 18 and 19 with respect to the mains voltage a phase- gc-controlled pulse voltages fbzw. g, the LO edges of which stimulate the flip-flops 16, 17 to emit the short ignition pulses.

The downtimes of the flip-flops 18 and 19 beginning at the trigger times are shown by arrows in the voltage diagrams d and c, with trigger times that occur during the previous dwell time with a cross and those that occur during a rest position of the flip-flops with marked with a circle.

When the switch 32 is flipped, the integrator 30 supplies one to the inputs of both integrators 24 and 25 increasing bias, which slowly shifts their output voltages into the negative. This will be First, the existing pulses according to the envelope 3 or 4 weaker and then less, whereby the Demagnetization is effected, depending on the circumstances of the case, it may additionally be necessary that to remove the workpiece to be demagnetized and the demagnetizing coil.

By turning the switch 37, the firing of the thyristor 7 can be prevented, so that the workpiece is fully magnetized.

The advantages achieved by the invention are in particular that a network supplied by the field-generating coil flows current in view of the demagnetization process with an opposite the mains frequency is much lower frequency effective, so that common, for continuous operation mil Line voltage and line frequency designed degaussing coils can be used, even with large volume Bodies a sufficient penetration depth is achieved and continuous operation is possible. In addition, the further embodiment of the invention has the advantage that; instead of a heavy, complex and maintenance-intensive one term converter or motor generator a power source is provided that the magnetization current while maintaining the connection of the coil to da; Netz supplies a small amount of space and material wall and is light and maintenance-free.

For this purpose 2 sheets of drawings

Claims (6)

Patent claims: 1. A method for demagnetizing a large-volume workpiece by means of an alternating magnetic field, the field strength of the alternating magnetic field being reduced by reducing the magnetizing current and / or by increasing the distance between the workpiece and the magnetizing coil, and where the frequency of the alternating magnetic field is lower than the mains frequency characterized in that a mains-frequency pulse or gap current is used as the magnetizing current, which is composed of pulse groups (Iu to / 15; / 21 to ht) of alternating polarity, the intensity of which slowly decreases monotonically and within which the intensity of successive pulses initially increases (Iu, / 12, In) and then decreases (In, / h. / Is). 2. The method according to claim I, characterized in that that the intensity of the pulses of each pulse group is essentially sinusoidal Envelope follows (Figs. 1 and 2). 3. The method according to claim 1, characterized in that that the intensity of the pulses of each pulse group is essentially triangular Envelope follows (Fig. 3). 4. The method according to claim 1, characterized in that for magnetizing the workpiece Pulse groups of one polarity are suppressed. 5. Circuit arrangement for performing the method according to claim 1 or the following, characterized in that the magnetizing coil (5) has two control units connected in antiparallel re rectifier (6, 7) on the supply network (terminals 36) and that a control device (8 to 31, 34 and 35) is provided to the first rectifier (6) during a sequence of positive Half-waves of the mains voltage and the second rectifier (7) during a subsequent, essentially equal sequence of negative half-waves of the mains voltage in each case Ignition pulses supplies, wherein the ignition pulses are controlled in the phase control so that the Amplitudes of the resulting, successive magnetizing current pulses within each The sequence first increase and then decrease, so that the envelope curve of the amplitudes becomes a Mains voltage is subharmonic. 6. A circuit arrangement according to claim 5, characterized in that between the output of a controlled with mains frequency, a 50 Hz square wave voltage supplying limiter circuit (20) on the one hand and the Z'indel electrodes of each of the two controllable rectifiers (thyristors 6, 7) on the other hand in each case one A chain of a second retriggerable monostable multivibrator (18, 19) with controllable downtime, a first monostable multivibrator (16, 17) emitting short ignition pulses of constant duration, a pulse amplifier (14.15) and an ignition transformer (12, 13) is connected, that the trigger inputs of the second monostable multivibrator (18, 19) respond to opposing pulse edges, that the control inputs of the second monostable multivibrator (18, 19) are connected to the outputs of two integrators (24.251, at whose inputs two mutually 180 ° out of phase , subharmonic square-wave voltages with a duty cycle of 0.5 lie at the mains frequency n, which is supplied by a frequency divider (22, 23) controlled with the 50 Hz square-wave voltage, and that the opposing triangular voltages (i.e. e) leading outputs of the integrators (24, 25) have such amplitudes and mean values that the service lives of the two retriggerable monostable multivibrators (18, 19) only during alternating half-periods (Tsi, Tsi) of the subharmonic oscillation by initially increasing the network period duration (Tn) falling below increasing and then decreasing values.