JPH01238290A - Device for eliminating influence of unnecessary magnetism - Google Patents

Abstract

PURPOSE:To effectively eliminate unnecessary magnetism with a simple device by disposing a magnetic substance member having a magnetic shielding function in the vicinity of an equipment, winding a coil vertically around the magnetism being a problem, and controlling a current through the coil. CONSTITUTION:It is assumed that a magnetic field HE due to earth magnetism to be shielded is present in the Z-Z1 direction of a color cathode-ray tube 1. The magnetic shield 2 is provided surrounding the main part of the tube 1. On the shield 2, the coil 3 is wound in a plane that crosses with the axis of the tube orthogonally. If the earth magnetism HE is present, an initial current generated when AC voltage is impressed to the coil 3 through a current waveform control circuit 4 comes to asymmetrical. The amplitude of this initial current is made small by the circuit 4 while maintaining or enlarging in ratio the asymmetry of the wave, and finally, the current no longer flows, thus the effect of the shield 2 by the AC current is given automatically. As a result, the influence of unnecessary magnetism can be effectively eliminated with a comparatively simple device.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an unnecessary magnetic influence removal device that makes electronic devices such as shadow mask type color cathode ray tubes less susceptible to the influence of surrounding magnetic fields such as terrestrial magnetism. It is something.

[Conventional technology]

Many devices are known, such as shadow mask type color cathode ray tubes, which avoid the influence of unnecessary magnetism such as earth's magnetism during their operation.

Various methods are known to prevent such devices from being affected by the problematic magnetic field. The first is the use of a well-known magnetic shield. A magnetic shield is formed by surrounding the device in question or specific parts thereof with a magnetic material of high magnetic permeability.

For example, in the case of the shadow mask type color cathode ray tube mentioned above, in order to prevent the influence of the earth's magnetism from affecting the path of the electron beam,
It is common practice to surround the outside of the funnel-shaped funnel section, which is the main path of the electron beam, with a magnetic material to form a magnetic shield.

In some cases, this magnetic shield is provided in the vacuum inside the funnel.

Further, as the shield material, a special alloy such as permalloy having a high initial magnetic permeability or an inexpensive soft iron plate is used.

Since soft iron plates have a low initial magnetic permeability, they are not as effective as they are, but in the presence of a magnetic field to be shielded, degaussing (usually translated as degaussing, but as will be explained later), in the presence of an ambient magnetic field, it becomes pure. The effective magnetic permeability can be increased by performing an operation (not a non-magnetizing operation), and it is usually used in this way.

The degauss operation is an operation in which an alternating magnetomotive force is applied to the shield member, starting from an amplitude at or above which the shield material is magnetically saturated, and whose positive and negative polarities are approximately symmetrical and gradually decrease toward zero.

Assuming this is done, a soft iron plate with a similar configuration (plate thickness, shape) can achieve a shielding effect that is quite similar to that of special materials such as permalloy.

However, as is well known, it is extremely difficult to create a perfect magnetic shield, and even in cases like the color cathode ray tube example mentioned above, ordinary shields are quite imperfect. If this is to be made more reliable, the thickness of the shielding material must be increased by 3 areas (the coverage ratio around the color cathode ray tube in question, for example).

However, such a shield increases the weight and price of the device, and the improvement in effectiveness is relatively small. This tendency is particularly noticeable in the case of color cathode ray tubes, because the phosphor screen cannot be surrounded by a shielding material.

The second method to remove the effects of unnecessary magnetism is to wrap a coil around the device in question and continue to pass direct current through it for the duration of the device's use, creating a magnetomotive force (magnetic field) that cancels out the unwanted magnetism. There is also a way to actively create

However, this requires a new DC current source, which increases power consumption, and also requires the troublesome work of adjusting the direction of the current to cancel the magnetic field. Regardless of its effectiveness, it cannot be used in all practical situations.

The third method of removing the influence of unnecessary magnetism was published in 1974-3.
There is a special method disclosed in Japanese Patent No. 1649. This is done by disposing a member exhibiting a magnetic shielding function near the device that avoids the influence of unnecessary magnetism from the outside, and by making sure that the member exhibiting the magnetic shielding function is magnetically saturated.
An alternating magnetomotive force that starts with a larger amplitude and whose positive and negative polarities are almost symmetrical and whose amplitude gradually decreases, and another magnetomotive force that does not converge to zero until at least a predetermined period of time has elapsed and monotonically decreases toward zero. The sum is added to the member exhibiting the function of the magnetic shield, and at this time, the other magnetomotive force is applied in a direction that strengthens the unnecessary magnetism that is the original problem.

[Problem to be solved by the invention]

This method can produce better effects than the first method if the size of the magnetic shield equivalent member is the same, and it requires continuous DC current (7 times) during the period of use of the device in question. However, in order to put it into practical use, it is necessary to know the direction of the unwanted magnetism in order to determine the direction of the above-mentioned "another magnetomotive force", and to set the direction of the above-mentioned other magnetomotive force. (-adjustment of the direction of the flowing current, albeit temporally) is necessary, and despite its effectiveness, it has many troublesome elements like the second method, so it cannot necessarily be said to be practical.

This invention was made in order to solve the above-mentioned problems, and it can be used without having to check the direction of magnetism whose influence should be removed every time. The objective is to obtain a device for eliminating the influence of unnecessary magnetism that is effective against unnecessary magnetism in one specific direction (regardless of sign) and that can improve the magnetic shielding effect simply by controlling the current waveform flowing through the degauss coil. shall be.

(Means for Solving the Problems) A device for eliminating the influence of unnecessary magnetism according to the present invention includes a magnetic member exhibiting a magnetic shielding function disposed near a device that avoids the influence of unnecessary magnetism, and a magnetic material member located near the magnetic material member. A coil is wound almost perpendicularly to the magnetic component in question, and when unnecessary magnetism is present, the peak of the current flowing through the coil becomes asymmetrical in positive and negative directions, and this is detected, and the current flowing through the coil is converged to zero. A current waveform control circuit is provided.

[Function] The current waveform control circuit of the present invention causes an alternating current with an amplitude exceeding the level at which the magnetic member is magnetically saturated to flow through the coil, and if there is a magnetic component of interest at this time, the current waveform changes with respect to a constant voltage. It detects that the current is asymmetric in positive and negative directions, and gradually converges the current while intentionally maintaining this asymmetry to eliminate the influence of unnecessary magnetism.

[Example] Hereinafter, an example of the apparatus for removing the influence of unnecessary magnetism of the present invention will be described based on the drawings. FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, and this FIG. 1 takes up a color cathode ray tube as a device that avoids the influence of unnecessary magnetism.

In FIG. 1, the symbol (■) is a color cathode ray tube, which has a tube axis Z-21 and has the characteristic of resisting the influence of magnetism in this direction. Reference numeral 2 denotes a magnetic material member having a magnetic shielding function, which is made of a magnetic metal as described later, and surrounds the main part of the color cathode ray tube 1 in order to bypass the magnetic flux in the 2-21 direction towards the color cathode ray tube 1. I'm here. Hereinafter, this magnetic member 2 will be referred to as a magnetic shield.

3 is a coil wound on the magnetic shield 2 in a plane perpendicular to the tube axis (to avoid the influence of magnetism in this direction).

4 is a current waveform control circuit which forms the main part of this invention;
It is connected in series to the coil 3, and AC input is supplied from the input terminal 5.

The details are described below.

As shown in the figure, the current waveform control circuit 4 in this embodiment includes two power transistors 10a arranged in opposite directions (antisymmetrical) and in parallel.

Two relatively large capacitance capacitors lla and llb are connected in series to each of the emitters 10b.

Resistors 12a and 12b for time constant adjustment are connected in parallel to capacitors lla and llb, respectively. The emitter of the power transistor 10a is connected to a connection point B via a parallel circuit of a resistor 12a and a capacitor lla. Connection point B is connected to one of the input terminals 5.

Further, the connection point B is connected to the collector of the power transistor 10b via a diode 14b for preventing discharge of the capacitor itb.

The emitter of power transistor 10b is connected to connection point A via a parallel circuit of resistor 12b and capacitor Ilb. Connection point A is connected to the other input terminal 5,
and a diode 14a for preventing discharge of the capacitor lla.
The collector of the power transistor 10a is connected to the collector of the power transistor 10a.

A POSISTOR 13 is connected between connection points A and B.

The POSISTOR 13 is connected in parallel with the entire current waveform control circuit 4 so as to be short-circuited therewith.

Next, the operation will be explained. It is assumed that there is a magnetic field Ht to be shielded in the Z-21 direction of a member that resists the influence of earth's magnetism, that is, the color cathode ray tube 1. Therefore, the magnetization curve vA (B-H curve) of the material of the magnetic shield 2 is
As shown in the figure. It is assumed that the magnetic field indicated by Ht in the figure is due to the earth's magnetism, which is the current problem, and the magnetic fields in the material that provide the saturation magnetic flux density are 10HH and HM, respectively.

Now, returning to Figure 1, when operating the color cathode ray tube l in the same way as the operation normally called degaussing,
An AC power source is connected to the input terminal 5. At the beginning of this operation, it is assumed that the POSISTOR 13 is in a conductive state and the current waveform control circuit 4 has no special function.

In this state, a current (initial current) flows through coil 1, but
This initial current is determined by at least the influence of the back electromotive force due to the magnetic flux generated in the magnetic shield 2 by the current itself.

Now, assuming that this initial current does not have the magnetic field H1 due to the earth's magnetism in the magnetic shield 2 in Fig. 1, the magnetic field that gives the saturation magnetic flux density is exactly between 10HM and -H, or is slightly larger than that. The number of turns of coil 3 so that the amplitude is
It is assumed that the resistance and applied voltage have been adjusted in advance.

It is assumed that the current in this case has a waveform as shown by a solid line 100 in FIG.

Next, if the same power source as above is connected to the input terminal 5 in the presence of the magnetic field Ht due to the earth's magnetism, the change in the magnetic field in the magnetic shield 2 due to the initial current immediately after that is the fourth
As shown at 110 in the figure, the whole is centered around H7 and is biased to the right (if H8 is positive, towards the positive side of H), and the positive peak exceeds the saturation magnetic field +H. Become.

The current I at this time has a waveform as shown by a dotted line 101 in FIG. 5, that is, the peak on the positive side is high and the peak on the negative side is low. The reason why the peak on the positive side becomes high is that when the value of the magnetic field H shown at 110 in FIG.
This is because the back electromotive force that had been suppressing the increase in the current suddenly decreases.

On the other hand, on the negative side, the opposite tendency appears to some extent, and the peak becomes lower.

That is, when the earth's magnetic field H4 exists, the coil 3 in FIG.
The initial current waveform when an alternating current voltage is applied to is asymmetrical in that the resulting magnetomotive force increases in the direction of increasing Ht, and decreases in the opposite direction.

Now, let's go back to Figure 1 and see what's new! T! When the l current waveform continues for a while (several tens of cycles or less), the temperature of the posistor 13 rises, its resistance increases, and the current no longer flows through the posistor 13, but instead flows through the power transistors lOa, 10b.

Now, the direction in which the current flows in the current waveform control circuit 4 from the connection point A to the connection point B drawn in the diagram is defined as the positive direction in FIG.

Considering this positive half cycle, initially the capacitor ILa
, 1. Since both lb are not charged, they are considered to be in a conductive state for alternating current, so the base and emitter of the power transistor 10a are at the same potential, and the current of the above voltage flows to the connection point - diode 14a - power transistor 10a - capacitor lla (resistance 12'a,
12b is assumed to be large enough to be ignored when considering this phenomenon) - flows in the direction of connection point B.

At this time, some charge is stored in the capacitor lla. Also, some charge is stored in the capacitor llb, but this is due to the base current of the power transistor loa and can be ignored. In the following, the base current is assumed to be sufficiently small.

Then, the negative half-cycle current flows in the same way at connection point B
- Diode 14b - Power transistor tob - Capacitor 1lb - Flows in the direction of connection point A, but at this time,
The base potential of power transistor tab is capacitor I
Because a slight current blocking bias is applied due to the charge stored in la, the dotted line lO1 in Figure 4 was originally
In the negative direction shown by , a small amount of current flows in a controlled manner (but still to a certain extent).

Repeat the above process, each time capacitor 12a
, 12b gradually stores charge, but as is clear from the process described above, the capacitor lla through which the positive direction current, which initially had a large amount of current, passes is replaced by the capacitor llb through which the negative direction current passes. More charges can be stored.

The current flowing through the coil 3 is blocked in the positive half cycle by charging the capacitor lla, and in the negative half cycle by biasing the power transistor lob to cut-off, the current gradually decreases until finally Almost no current flows.

Moreover, the current in the positive direction is consistently maintained larger during the process. (Note that diodes 14a, 14b are placed in part to prevent the charge stored in capacitors lla, llb from discharging through the transistor circuit in the next half cycle).

In other words, the asymmetry of the initial current caused by the existence of H9 is maintained or proportionally expanded while the current amplitude decreases, and eventually almost no current flows. That is, a current as shown at 102 in FIG. 6 can be automatically passed through the coil 3.

If the geomagnetic field H9 that existed from the beginning is in the opposite direction to the above explanation, the current flowing from connection point B to A will be larger, preventing transistor 10a from being cut off in the positive half cycle. , during the negative half cycle, the capacitor llb is charged and stabilizes in a blocked state, and the waveform during this period is opposite to that shown in FIG.

Furthermore, if the component of the earth's magnetic field in the Z-21 direction is 0 from the beginning,
If so, the current in the positive half cycle (current flows from the connection point A to B) and the negative half cycle (current flows from the connection point B to A) at least in the power transistors 10a and 10.
At the beginning when the current starts flowing in the direction of b, the values are almost the same.

-a, in such a circuit, some variation in characteristics is unavoidable, so as the current cycles back and forth, the charge accumulated in one capacitor becomes larger than the other, and eventually the positive and negative An unbalanced current waveform in which either one is dominant will converge to zero, but if the peak of the current value becomes sufficiently small before the unbalance becomes noticeable, it will essentially become the conventionally known degauss. You will get the same effect as the operation.

In the end, as will be described later, the effect of the magnetic shield 2 is automatically increased by the alternating current with a special waveform, without having to measure the direction of the earth's magnetism and set the waveform accordingly. Become.

In order for this automatic waveform control to be carried out stably, it is necessary that the capacitor lla not be charged too rapidly and that this should be done by repeating several cycles, and the resistor 12a is also used for this purpose. It will be done. Its value should be determined experimentally.

Note that if this value is too small, the current will continue to flow through the coil 3, causing damage to the equipment that should be shielded.
For example, it may have an undesirable effect on the operation of the color cathode ray tube 1, but in this case, when a conventionally known voltage is applied, the resistance becomes O with a certain time constant, such as a thermistor. It is possible to apply a technique conventionally known as a degauss circuit used in color televisions, such as connecting a wire to the coil 3 in parallel.

An example of this is shown in FIG. In this FIG. 2, 15 is a thermistor. The time constant of the thermistor 15 must be greater than the it current source control circuit 40 time constant.

The POSISTOR 13 is used so that the phase of the power supply voltage at the moment when the AC power supply is connected to the input terminal 5 does not affect the asymmetry of the current in the coil 3 later.

For example, in the case where H4 is positive, if the AC power supply is turned on in the phase where negative current flows, capacitor 16 will be charged first, and the subsequent current waveform will be completely opposite to what is required. It may be asymmetrical.

The selection of the sizes of the resistors 12a, 12b mentioned above is also important in relation to this problem. Resistor 12a.

If 12b is made sufficiently low and the amount of charge per cycle is reduced, it is possible that the POSISTOR 13 can be omitted.

If the resistors 12a and 12b are made smaller, a thermistor 15 as described in connection with FIG.
It is also possible to configure .

An example of this is shown in FIG. In this FIG. 3, 16a,
16b is a POSISTOR in place of the resistors 12a and 12b.

Here, returning to FIG. 1 again, this embodiment is effective when the component of unnecessary magnetism (earth's magnetism) is oriented in the Z-21 direction, and for magnetism perpendicular to this, conventional general magnetic It is only as effective as shielding and normal degaussing (with symmetrically decaying alternating currents).

However, a device that avoids the influence of magnetism is the color cathode ray tube.
In such cases, the direction of the most harmful magnetism is often fixed, and the coils can be arranged with that direction mainly taken into consideration.

Note that it is of course possible to select the material and determine the structure of the magnetic shield 2 based on this method.

The main point of this invention described above is that a coil 3 having a winding surface perpendicular to the magnetism is provided in a magnetic material suitable for a space where unnecessary magnetism exists, and a sine wave alternating current voltage of an appropriate amplitude is applied to the coil 3. If the impedance of this AC power source is sufficiently low, the flowing radio wave waveform will be asymmetrical between positive and negative. Based on this, the current waveform control circuit 4 is operated, and by applying the principles described later, etc., the influence of unnecessary magnetism is suppressed. The current waveform control circuit 4 is not limited to the one described here.

In some cases, it is also possible to create something more precise using a complex waveform analysis circuit.

Note that the asymmetry of the current waveform can be approximately determined by the magnitude of the second high-frequency component of the original AC radio frequency, and therefore, the current waveform control circuit 4 detects the second high-frequency component. Of course, a method that determines the operation is also possible.

Of course, even with a simple circuit as described in this embodiment, auxiliary means for stabilizing the operation of the power transistors 10a and 10b can be considered.

Next, it will be explained in principle that the current waveform control according to the present invention is effective in removing the influence of unnecessary magnetism.

First, the principle of -S magnetic shielding will be explained.

To make the problem easier to understand, we will consider it in terms of a model, and as shown in Figure 7, the density B0, which corresponds to geomagnetism, etc.
When a bar-shaped ferromagnetic bar ba (hereinafter simply referred to as a magnetic bar), which corresponds to a magnetic shield such as mild steel, is placed in a space where unnecessary magnetic flux such as ), and consider how the magnetic flux density changes at a nearby location, for example, the location indicated by point α.

FIG. 8 shows the magnetic flux distribution when the magnetic bar ba is placed in the dotted line area shown in FIG. 7.

In FIG. 8, considering the total magnetic flux that crosses the X-XI plane, the total magnetic flux at sufficiently far left and right sides must be the same as in FIG. 7.

However, the magnetic flux tends to gather in the magnetic bar ba with low magnetic resistance, and therefore the magnetic flux density decreases in the vicinity of the α point near the magnetic bar ba. This is the principle of magnetic shielding.

That is, in order to obtain the effect of magnetic shielding, it is desirable to increase the number of magnetic fluxes passing through the magnetic bar ba, that is, the magnetic flux density in FIG. 8.

Figure 9 shows the so-called magnetization curve of the material of the magnetic bar ba for considering changes in magnetic flux within the magnetic bar ba. The explanation will be based on.

For convenience of explanation, the magnetic flux density in the magnetic bar ba varies somewhat depending on the location within the magnetic bar ba itself, but in the following explanation, it will be considered as -.

Now, it is assumed that the magnetic bar ba is initially magnetically neutral, that is, at the 0 point in FIG.

As shown in FIG. 8, such a magnetic bar ba is placed in a space with a magnetic flux density B0 corresponding to --like earth's magnetism (and the magnetic state of the magnetic bar ba is at point P (magnetic field 14P).

Moving on to magnetic flux density BP).

At this time, as described above, the magnetic flux due to the earth's magnetism tends to gather within the magnetic body, so B P > Bo.

Further, the magnetic field H2 is smaller than the magnetic field in the space due to earth's magnetism in the case of FIG. 7, and this is because the magnetic bar ba is slightly magnetized, resulting in a so-called self-magnetic force.

In order to increase the effectiveness of the magnetic bar ba in FIG. 8 as a magnetic shield for the α point, it is preferable that the value of the magnetic flux density BP be as high as possible.

For this reason, devices such as color television receivers are usually devised to perform an operation called degaussing of the magnetic shield, which apparently increases the effectiveness of the magnetic shield.

As mentioned above, the degauss operation of a magnetic shield involves applying a strong alternating magnetomotive force (the magnetic field generated by the alternating current of ordinary power lines is used as it is) to the shield material, and then applying this alternating magnetomotive force to the positive and negative symmetrical This is an operation that gradually weakens the power while essentially maintaining it, and finally converges to zero.

jTM FIG. 10 shows how the magnetic bar ba in FIG. 8 is subjected to a conventional degauss operation. In FIG. 10, 20 is a coil wound around a magnetic bar ba;
1 indicates a power source for supplying current to this coil 20.

As shown in FIG. 11, this power source 21 is capable of supplying an alternating current to the coil 20 whose amplitude decreases over time. The peak value of this current is at least the first few cycles of the alternating current when the magnetic rod ba
It is designed to generate sufficient magnetomotive force to saturate the passing magnetic flux.

Fig. 12 shows the change in the magnetic state when the conventional degauss operation is performed on the magnetic bar ba in Fig. 8 while it remains in the same position.At first, the magnetic state of the magnetic bar ba is at point P. However, when an alternating magnetomotive force is applied, the peak is strong enough at first, so the point at which the state changes is the outermost circumference of the magnetization curve, that is, point a in Fig. 12.
-b-c-d, but as the peak becomes a little smaller, the side where the apparent magnetomotive force due to the earth's magnetism and the alternating magnetomotive force due to the coil are added, that is, the part at point a. However, while the apparent magnetomotive force of the earth's magnetism and the alternating magnetomotive force due to the coil decrease each other, in other words, the state point no longer passes through the 0 point, and B b
It begins to take a route like C1al.

Furthermore, when the peak value of the alternating magnetic field becomes smaller, the state points no longer pass through point a, for example, al b + - c, - d
, and when the alternating magnetomotive force converges to zero as the figure continues to become smaller, the magnetic state point of the magnetic bar ba is at point P' (magnetic field H2', not shown). Moving on to the magnetic flux density B,').

At this time, as can be inferred from the above-mentioned convergence process, point P' in FIG. 12 is above point P, that is, BP'
> BP, in other words, the magnetic flux passing through the magnetic bar ba increases compared to before degaussing, and near point α in Figure 8, the magnetic flux density decreases by that amount, resulting in a magnetic shielding effect. will be increased.

As shown in FIG. 13, the shape and arrangement of the color cathode ray tube 1 and the magnetic shield 2 are different from the horizontal shape shown in FIG. 7 or 8, the magnetic shield 2 is replaced with the magnetic bar ba, the degaussing coil 3 is replaced with the coil 20 in FIG. 10, and the alternating current supply bag W4a is replaced with the electric current supply bag W4a in FIG. If a21 and one point in the portion of the cathode ray tube 1 that is substantially surrounded by the magnetic shield 2 are made to correspond to the α point, the same explanation as above can be applied in terms of the operating principle. .

However, with a color TV receiver, it is not possible to perform the degauss operation while the screen is displayed, so it is possible to perform this operation automatically when the screen is not displayed, for example, the moment the power switch is turned on. It has been devised.

Hereinafter, the explanation will be given again with reference to FIG.
In order to reduce the magnetic flux density near the α point by placing a It was important that the magnetic flux be concentrated.

In other words, in order to increase the shielding effect, after applying a degauss operation to the magnetic bar ba, the state point on the magnetization curve state diagram as shown in Figure 8 of the magnetic bar ba should be moved in the direction of the highest magnetic flux density as possible. Just let it go up.

By the way, in Fig. 12, point P' is above point P,
In other words, we were able to make BP<B,' because when we apply an alternating magnetomotive force that attenuates while substantially maintaining the positive and negative symmetry to the magnetic bar ba as a degauss operation, the earth's magnetism is added to it. This is because the actual alternating magnetomotive force is asymmetric.

The method described here, which was developed with attention to this point, intentionally gives an asymmetrical characteristic to the alternating magnetomotive force applied to the magnetic shield, that is, the horizontal magnetic bar ba shown in Fig. 10, during the degauss operation. This is to improve the shielding effect of

FIG. 14 shows the waveform of the alternating magnetomotive force when the horizontal magnetic bar ba in FIG. 1O is degaussed using this method, and therefore the waveform of the radio waves flowing through the coil 20.

This current waveform is a section 1 of a substantially symmetrical damped alternating electromotive force based on the DC component 10. and an attenuation section L2 of this DC component I0. The direction of the direct current 10 is selected to further increase the 153 flux due to the earth's magnetism passing through the magnetic bar ba, that is, to strengthen the external magnetic field that is currently being shielded.

The explanation returns to FIG. 12 again. Considering the effect of this degauss operation on the phase diagram of the magnetization curve, the section t in Fig. 14
At the end of l, that is, when the attenuation of the alternating damped magnetomotive force is completed, the state of magnetization of the magnetic bar ba moves to a point where both the magnetic flux density B1ft and the field H are large, such as point P. This is because a DC component of magnetomotive force is applied from the outside.

Next, at the end of section L2 in FIG. 14, that is,
When the magnetomotive force is completely attenuated by the DC current, the magnetization state of the magnetic bar ba shifts to a point such as point P#. At this time, on the magnetization state diagram of the magnetization curve in Figure 12, P
The 'point' is always on the upper left side compared to the P' point.

As is clear from the above operations, the magnetic bar ba
This is because it is slightly permanently magnetized by the magnetomotive force caused by the DC current.

However, for this reason, the magnetic flux density in the magnetic bar ba, and therefore the total magnetic flux, has increased, and as mentioned above, the total magnetic flux crossing the X-XI plane in Figure 8 is sufficiently far away on the left and right sides of the figure. Considering that the total magnetic flux must be the same as the total magnetic flux of the magnetic bar ba, the magnetic flux density at a point slightly away from the magnetic bar ba, such as the α point, can be made much smaller than in the case of conventional degauss operation. .

By the way, the above explanation is a formal discussion focusing only on magnetic flux density, and in reality, the magnetic bar ba is slightly permanently magnetized, as is clear from the above operation. , Therefore, if point P' on the magnetization state diagram of the magnetization curve in FIG. At point P'' in the figure, that is, at the time when degaussing is completed by this method, it can be considered that lines of magnetic force shown by dotted lines in FIG. 15 are newly added to the magnetic bar ba.

As a result, if the point considered for -S is very close to the magnetic bar ba, for example, point α' in Figure 15, a magnetic field in the opposite direction to the ground (R) is generated. Moreover, this amount largely depends on the magnitude of the DC magnetomotive force corresponding to the DC component! described in connection with FIG.

However, even if a slightly opposite magnetic field occurs in the vicinity of the magnetic bar ba, if the magnitude of the DC magnetomotive force corresponding to the DC component I0 is appropriately adjusted, the desired point, for example α It is true that the magnitude of the magnetic field at a point, and therefore the magnetic flux density, can be made significantly smaller than when applying the conventional degauss operation.

Although the above explanation is based on a horizontal type using a magnetic rod ba, the same principle can also be applied to a color cathode ray tube as shown in FIG.

In order to apply unnecessary external magnetism to the color cathode ray tube 1, in the case of FIG. By the device 4a, the fourteenth
Just supply the current as shown in the figure.

In this case, the direct current component I. The direction of is selected to substantially increase the unnecessary energy passing through the color cathode ray tube 1, and the direct current component ■. The size of is the 15th
It may be selected while taking into account the phenomena explained in connection with the figure.

According to experiments, when the object is the earth's magnetism, the magnitude of the magnetomotive force due to the DC component I0 is within several times the actual magnetomotive force due to the earth's atmosphere in the case of a color television receiver with an ordinary magnetic shield. .

As is clear from the principle, this value is also related to the material of the magnetic shield, and should be determined mainly experimentally, together with the selection of the material.

Since the magnitude and direction of the DC component I0 must be selected depending on the orientation of the color cathode ray tube 1, practically, the alternating current supply device 4a has a built-in device for changing the magnitude and magnetism of the DC component. is preferable.

In the example shown in Fig. 13, this method
Valid only for components parallel to the direction.

However, the same effect as normal degauss is guaranteed for components in the direction perpendicular to this.

In this method, the magnetomotive force applied to the magnetic shield does not necessarily have to be as shown in FIG. 14, but may be as shown in FIG. 16, for example. The key points are a damped alternating magnetomotive force whose positive and negative sides are substantially symmetrical starting from a sufficiently large amplitude, and a magnetomotive force that monotonically decreases toward zero in only one direction without converging to zero faster than this damped alternating magnetomotive force. It is sufficient if it can be regarded as the sum of

〔Effect of the invention〕

As described above, according to the present invention, a magnetic material member having a magnetic shielding function is placed near a device that avoids the influence of unnecessary magnetism, and a coil is wound almost perpendicularly to the magnetic component in question. When an alternating current with an amplitude exceeding the level at which the magnetic material is magnetically saturated is passed, and there is a problematic magnetic component, it is detected that the current waveform becomes asymmetric in positive and negative directions with respect to a constant voltage, and this is detected as intended. Since the current is configured to gradually converge to zero while maintaining a constant current, the influence of unnecessary external magnetism can be effectively removed using a relatively simple device. This has the effect of allowing the device to operate with high performance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an apparatus for eliminating the influence of unnecessary magnetism according to one embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing other embodiments of the present invention, and FIG. 4 is a detailed diagram of the present invention. FIG. 5 is an explanatory diagram showing that an asymmetrical current flows through the coil due to the asymmetric magnetic field shown in FIG. 4. FIG. 6 is a waveform diagram showing the current waveform of the current waveform II1gJ circuit in this invention. , FIG. 7 and FIG. 8 are explanatory diagrams showing the relationship between unnecessary magnetism and magnetic shielding, respectively, to explain the removal of unnecessary magnetism according to the present invention, and FIG. 9 is a magnetization curve to explain the removal of unnecessary magnetism according to the present invention. Figure 10 is a diagram showing how the magnetic bar in Figure 8 is degaussed, Figure 11 is a waveform diagram showing the coil current in Figure 10, and Figure 12 is the magnetic bar in Figure 8. E, which shows the change in magnetic state when degaussing is performed on
Figure 13 shows an example of the case where the magnetic member and coil of the present invention are applied to a general color receiver, and Figure 14 shows the current waveform to obtain the magnetization curve of Figure 12. 15 is an explanatory diagram showing the distribution of magnetic lines of force corresponding to the completion of the degauss operation in the magnetization curve of FIG. 12, and FIG. 16 is a diagram of the waveform shown in FIG. 14 for obtaining the magnetization curve of FIG. 12. FIG. 3 is a waveform diagram showing different current waveforms. 1... Device that avoids the influence of unnecessary magnetism, 2... Magnetic material member, 3... Coil, 4... Current waveform control circuit. In addition, the same reference numerals in the drawings represent the same or ti+part bone parts.

Claims (1)

[Claims] A magnetic member with a magnetic shielding function is placed near the device to avoid the influence of unnecessary magnetism, a coil is wound near the magnetic member almost perpendicularly to the magnetic component in question, and this When the coil is connected to an AC power source where the voltage changes symmetrically between positive and negative, if the unnecessary magnetism is present, it is detected that the peak of the current flowing through the coil becomes asymmetric between positive and negative, and the current flows through the coil while maintaining this asymmetrical tendency. An unnecessary magnetic influence removal device equipped with a current waveform control circuit that gradually converges to zero.