JPH0159757B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic shielding device that is particularly suitable for use in shielding experimental equipment, measurement equipment, etc. from weak magnetic fields. It has been improved so that it can be used in an effective state.

Magnetic shielding devices using magnetic materials often have a multilayer structure in order to enhance the magnetic shielding effect. Shapes include a spherical shell, a cylinder, a cube similar to these, and a cylinder with an arbitrary cross-section, but cylindrical magnetic shielding devices are often used from the viewpoint of ease of manufacture.

However, conventional magnetic shielding devices do not always exhibit the same high magnetic shielding effect as immediately after heat treatment, and the effectiveness gradually deteriorates. The reason for this is as follows.

Magnetic shielding devices are manufactured by processing and welding magnetic plate materials, demagnetized by heat treatment, and then assembled by spot welding. Immediately after heat treatment, the magnetic resistance device manufactured by such a process exhibits a high magnetic resistance effect due to its demagnetization effect. However, if the material is left in a magnetic field due to its resistance, the magnetic material itself becomes gradually magnetized, and the resistance effect gradually deteriorates. In addition, when the device is used in a magnetic field, the magnetic material is magnetized and the magnetic shielding effect deteriorates when the device is subjected to impact, strain, or temperature changes. do. Furthermore, even if a strong magnetic field is applied for only a short period of time, the magnetic material becomes magnetized, resulting in a deterioration of the shielding effect.

As mentioned above, the reluctance effect of a magnetic repellent device deteriorates due to magnetization for various reasons, so if you especially dislike weak magnetic fields, you can use some method to remove the refractive effect that has deteriorated due to magnetization immediately after heat treatment. need to be restored to that state. As one method for this, an AC demagnetization method is known.

However, even if demagnetization is performed using the AC demagnetization method, the damping effect begins to deteriorate immediately after demagnetization.
Furthermore, AC demagnetization requires a sufficient amount of time to slowly attenuate the amplitude of the excitation current.

Conventionally, AC degaussing is performed when it is determined that the magnetic demagnetization device has deteriorated due to magnetization, or for example every month, but AC degaussing devices are generally not available at hand, You can remove it from an experimental or measuring device, wrap a degaussing coil around it to demagnetize it, then remove the coil and return it to its original location, or transport it to an AC demagnetizer in another location, demagnetize it, and put it back in place. was.

Therefore, in the past, it took a considerable amount of time after demagnetization before it could actually be used, and during that time it had already been magnetized and began to deteriorate, so when it was actually used, it remained in the state of the highest magnetic resistance effect, the same as immediately after heat treatment. It was very difficult to use magnetic shielding equipment.

The present invention solves the above-mentioned problems of the prior art and provides a magnetic shielding device that can be used in a state where it has the same high magnetic shielding effect as immediately after heat treatment whenever it is used. With the goal.

The purpose of this is to have an AC demagnetizing coil wound around a magnetic shield box, and also to have an AC demagnetizing power supply supplying an AC demagnetizing excitation current to this coil.
This can be achieved through ideas that have never been thought of before.

The present invention will be explained below with reference to the drawings. Fig. 1 shows an embodiment of the device of the present invention, Fig. 2 shows the arrangement of AC demagnetizing coils, Fig. 3 shows a bottom plate convenient for arranging the coils, and Fig. 4 is suitable for AC demagnetizing. This shows the amplitude change of the excitation current.

In these figures, reference numeral 1 is a single-layer magnetic shielding box with a cylindrical bottom made of ferromagnetic material, and an AC demagnetizing coil 2 is parallel to the central axis of the magnetic shielding box 1, as shown in Figure 2. It is placed in the same direction. As a result, a demagnetizing magnetic field is generated around the axis of the magnetic shielding box 1. 3 is a bottom plate that protects the AC demagnetizing coil 2, and as shown upside down in FIG. 3, grooves 4 for passing the coil 2 are formed radially on the lower surface 3a of the bottom plate 3. The bottom plate 3 is placed on the bottom surface 1a of the magnetic shielding box 1, as shown in FIG. 1, so that the bottom surface 1a and the grooves 4 face each other. A hole 5 for arranging the coil is drilled in the center of the bottom surface 1a of the magnetic shield box 1, and this hole 5 and the groove 4 of the bottom plate 3
An alternating current demagnetizing coil 2 is disposed through it.

Reference numeral 6 denotes an electromagnetic shielding plate, and one or more layers made of a high electrical conductivity material are installed along the inner circumference of the magnetic shielding box 1. This electromagnetic shielding plate 6 is provided to prevent electromagnetic induction noise from being induced inside the magnetic shielding device due to the presence of the AC demagnetizing coil 2, thereby preventing the shielding effect from deteriorating. Therefore, if electromagnetic shielding is not required, for example if the equipment inside the magnetic shielding device has a metal case with a shielding effect, or if electromagnetic noise does not interfere with measurements, etc. The electromagnetic shield plate 6 is not required.

As shown in FIG. 1, the AC demagnetization coil 2 is connected to a power source 7 for an AC demagnetization excitation current. By closing the demagnetization start switch 8, the power supply 7 starts supplying the AC excitation current _IH to the AC demagnetization coil 2, and then slowly attenuates the current amplitude. Therefore, a normal power source used for AC demagnetization may be used, but in this embodiment, in order to ensure removal of residual magnetism, an AC excitation current _IH with time-amplitude characteristics as shown in Fig. 4 is supplied. It is as follows. That is, in FIG. 4, the AC amplitude of the excitation current for AC demagnetization flowing through the AC demagnetization coil 2 is (1) zero at the demagnetization start time 0 determined by closing the demagnetization start switch 8, and (2) After that, it gradually increases with time t, and (3) the current value I _HO is reached at which the number of ampere turns (for example, 20 to 60 ampere turns) is sufficient to sufficiently saturate the ferromagnetic material of the magnetic shield box 1. At some point, the amplitude stops increasing, (4) then the current amplitude gradually decreases, (5) the current amplitude reaches zero at time T (for example, 30 to 60 seconds after the start of demagnetization), and (6) then it starts again. The current amplitude increases, (7) the amplitude stops increasing when the current amplitude reaches 1/3 to 1/5 of the previous I _HO , and (8) the current amplitude gradually decreases again. , (9) The current amplitude becomes zero at time 2T (for example, 60 to 120 seconds after the start of demagnetization) and returns to the state before the start of demagnetization.

Here, in FIG. 4, the reason why AC demagnetization is performed twice and the current peak value of the second time is made smaller than that of the first time will be explained. The AC demagnetization power supply 7 increases and decreases the amplitude of the AC excitation current I _H to be supplied as shown in FIG. The purpose is to perform AC demagnetization after saturating the magnet sufficiently. In the second AC demagnetization, the peak value of the AC amplitude is set to 1/3 to 1/5 of the first time, and the time change rate of the AC amplitude is made to be 1/3 to 1/5 of the first time. The purpose is to reduce the amount of amplitude change during one cycle of alternating current to ensure removal of residual magnetism in a low magnetic field.

When using the magnetic demagnetization device described above, it is sufficient to operate the demagnetization start switch 8 of the AC degaussing power source 7 immediately before using the device to perform measurements or the like. By closing this switch 8, AC demagnetization is automatically and easily carried out in just a few tens of seconds, and no matter who does it, there are no individual differences. It can be used as long as it is effective.

In the above embodiment, the magnetic shielding box 1 is described as having a single layer with a cylindrical bottom, but it may have any shape, be bottomless, or be made of multi-layered ferromagnetic material. The present invention can be similarly applied to any case. Further, the electromagnetic shield plate 6 is also unnecessary unless the electromagnetic shield is required.

As explained above, the magnetic desiccant device of the present invention can be operated easily, automatically, easily, in a short time, without any individual differences, and reliably produces the same high desiccant effect as immediately after heat treatment. can be used.

[Brief explanation of drawings]

The figures relate to the present invention; FIG. 1 is a partially cutaway configuration diagram of the magnetic shielding device, FIG. 2 is a perspective view showing the arrangement of AC demagnetizing coils, and FIG. 3 is for coil protection. FIG. 4 is a perspective view showing the bottom plate upside down, and FIG. 4 is a diagram showing an example of the relationship between time and amplitude of the excitation current for AC demagnetization. In the drawing, 1 is a magnetic shielding box, 2 is an AC demagnetizing coil, 3 is a bottom plate for protecting the coil, 4 is a groove drilled on the bottom surface of the bottom plate to pass the AC demagnetizing coil, and 5 is a groove on the bottom of the magnetic shielding box. The drilled hole for passing the AC demagnetizing coil, 6 is the electromagnetic shield plate, 7 is the AC demagnetizing power supply,
8 is a demagnetization start switch.

Claims (1)

[Claims] 1. A magnetic shielding box made of a ferromagnetic material consisting of at least one layer, a demagnetizing coil wound around the magnetic shielding box, and an AC demagnetizing power supply supplying an AC demagnetizing excitation current to the demagnetizing coil. A magnetic shielding device characterized by comprising: