JPH03158784A - Instrument and system for measuring magnetic permeability - Google Patents

Abstract

PURPOSE:To measure the magnetic permeability even when a magnetic shield material, etc., is in a plate shape by fitting an electromagnet to a high-rigidity base across an elastic body opposite the side of a surface to be measured and fitting a strain gauge to the elastic body. CONSTITUTION:The magnetic permeability measuring instrument is constituted by fitting the electromagnet 3 to the internal surface of the U-sectioned high-rigidity base 1 on the opposite side from the opening side across the elastic body 2, and a transducer detect the magnetic permeability from the detected value of the strain gauge 4 fitted with the elastic body 2 and the value of a supply current to the electro magnet 3. The opening flank end surface of the base 1 is made to abut on the body 6 to be measured such as the magnetic shield material and a constant interval is secured between the abutting surface and the tip of the electromagnet 3. The electro magnet 3 is constituted by winding a coil 3b around the outer periphery of an iron core 3a and its one end is extended to the opening side of the base 1. The coil 3b is connected to a DC power source through a current controller 9 and the supply current is varied under its control to vary a produced magnetic field. The value of the current supplied to the current supply circuit is inputted to the transducer through an A/D converter.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for easily measuring the magnetic permeability of a magnetic shielding material used in a magnetically shielded room such as a room in which a magnetic resonance diagnostic instrument (MHI) is installed. The present invention relates to a measuring device and a measuring system.

[Prior art] The magnetic permeability μ of non-magnetic materials is 1, and that of pure iron is approximately 8000.
It is known that the higher the magnetic permeability, the higher the magnetic shielding effect. For this reason, in order to know the magnetic shielding performance, the magnetic permeability of the magnetic shielding material has been measured.

The conventional measurement method is generally carried out in accordance with the magnetic property test of electromagnetic soft iron plate of iron W4JIs C2504.

First, a ring sample with an outer diameter of 45+*aw and an inner diameter of 33 mm is cut out, polished, and then magnetically annealed to create a sample with the best magnetic properties. Next, a search coil for detecting magnetic flux density and an excitation coil for applying a magnetic field are each wound a predetermined number of turns around the outer periphery of the ring sample. Then, a current is passed through the excitation coil, and the magnetic flux density is determined from the voltage generated in the search coil at that time, and the B-8 curve is determined by continuous measurement. The B-8 curve represents H (La field: unit Oe Oersted) on the horizontal axis and B (magnetic flux density: unit G Gauss) on the vertical axis, and from the slope of the B-8 curve (B/H) The magnetic permeability μ was determined and used as a criterion for determining whether the magnetic shielding effect was good or bad.

[Problems to be Solved by the Invention] Conventionally, when measuring the magnetic shielding effect of a certain material, a ring-shaped sample is cut out and its magnetic permeability is measured. That is, the measured value is obtained when the magnetic properties of the object to be measured are the best for the material. However, the construction of magnetic shielding walls in MRI rooms, etc. requires magnetic annealing of plate-shaped magnetic shielding materials, then drilling and on-site installation.
The magnetic shield wall is completed by welding. Therefore, the magnetic properties deteriorate due to the mounting process on the magnetic shield wall, resulting in magnetic shield properties different from the initially measured magnetic permeability.

For example, after magnetically annealing a pure iron plate, the B-8 curves of the ring sample in the as-cut state and the one magnetically annealed again are shown in FIG. As shown in FIG. 3, even if a material is magnetically annealed, its magnetic properties deteriorate when it is subsequently subjected to cold working. Therefore, after processing, it is necessary to measure the magnetic permeability of the magnetic shielding material to confirm whether the magnetic properties are higher than a predetermined value.

However, at present, there is no device to measure the magnetic permeability of plate-shaped magnetic shielding materials processed as magnetic shielding walls, and when designing, calculations are performed based on the best magnetic properties, and the materials used are selected based on the safety factor. It's getting thicker. In addition, the magnetic shielding effect can only be confirmed in the MRI room after the building has been completed and the equipment is in operation, so it is extremely difficult to take countermeasures when a negative result is obtained in a later test of the magnetic shielding effect. be. Therefore, a thick magnetic shielding material with a high safety factor must be used in advance, which increases the cost and is uneconomical.

The present invention makes it possible to measure magnetic permeability even when a magnetic shielding material is in the form of a plate, so that it is possible to accurately measure the value when it actually functions as a magnetic shielding material after processing, rather than the best value immediately after magnetic annealing. The purpose is to

[Means for Solving the Problems] The magnetic permeability measuring device of the present invention has an electromagnet facing the measurement surface side, which is attached to a highly rigid support material via an elastic body, a strain gauge is attached to the elastic body, and the detected value is measured. and a converter that converts the magnetic field into magnetic permeability based on the magnetic field of the electromagnet. In order to change the magnetic field caused by the electromagnet, it can be connected to a DC power source via a current control device.

The magnetic permeability measurement system of the present invention uses a magnetic permeability measurement device equipped with the electromagnet described above, and measures the magnetic field (H) and magnetic flux density (B) with a converter by sweeping the input current value to the electromagnet. The continuous B-H curve is detected in real time, and the magnetic permeability is determined based on the B-8 curve.

[Operation 1] When measuring the magnetic permeability of a plate-shaped magnetic shielding material using the magnetic permeability measuring device, a highly rigid support material is brought into contact with the magnetic shielding material. In this state, the magnetic field (H) of the electromagnet acts on the magnetic shielding material with high magnetic permeability, generating a high magnetic flux density proportional to the magnetic permeability, and the M magnet is attracted by the Coulomb force with a force proportional to the magnetic flux density. As a result, strain occurs in the elastic body to which the electromagnet is fixed, and the strain is detected by the strain gauge and input to the transducer. The magnetic field can be changed by changing the current supplied to the electromagnet, and a converter that receives a signal corresponding to the current value converts it into a corresponding magnetic field (H).

The converter has a calculation unit that converts strain into magnetic flux density (B) and a calculation unit that converts the magnetic flux density and magnetic field (H) into magnetic permeability, and calculates the magnetic permeability of the magnetic shielding material. do. That is, in the converter, a B-8 curve is obtained from the detected value of the strain gauge at each magnetic field value and the magnetic field, and the magnetic permeability μ is calculated by further obtaining the gradient (B/H).

[Example] An embodiment of the present invention will be explained with reference to FIG. 1.2.

The magnetic permeability measuring device has an electromagnet 3 attached to the inner surface of a highly rigid support member l having a U-shaped cross section on the side opposite to the opening side through an elastic body 2, and detects the detected value of a strain gauge 4 attached to the elastic body 2. The converter 5 detects the magnetic permeability from the current value supplied to the electromagnet 3.

The end face of the open side of the high-rigidity support member 1 is designed to come into contact with an object to be measured 6 such as a magnetic shielding material, and a certain distance is ensured between the contact face and the tip of the electromagnet 3. It looks like this. Note that the high-rigidity support material l is formed of a non-magnetic material.

The elastic body 2 is a magnetic body formed in a cylindrical shape, and in this embodiment, three strain gauges 4 are attached to its outer circumference at equal intervals. When strain occurs in elastic body 2, 3
The strain measuring device 7 receives the detected values of the two strain gauges 4 and outputs the average value of the three points to the converter 5.

The electromagnet 3 is constructed by winding a coil 3b around the outer periphery of an iron core 3a, one end of which is connected to the opening side (measurement surface side) of the high-rigidity support member l.
It is now heading towards The coil 3b of the electromagnet 3 is connected to a DC power source 8 via a current control device 9, and the supplied current is changed under the control of the current control device 9 to change the generated magnetic field. Further, the current value supplied to this current supply circuit is input to the converter 5 via the A/D converter IO.

The converter 5 includes a combinator that stores the relational expression of the magnetic field generated according to the value of the current supplied to the electromagnet 3 and the relational expression between the strain value of the strain gauge 4 and the magnetic flux density, which are obtained by calculation or experiment in advance. ing. The computer also has a calculation section that converts the detected value from the strain gauge 4 into a magnetic flux density (B), and also has a calculation section that detects the magnetic field (H) from the current value supplied to the electromagnet. The converter 5 also sweeps the current value to the electromagnet 3.
The magnetic flux density (B) and magnetic field (H) are measured simultaneously, and a continuous H curve can be displayed on the CRT (display unit) 5a, and the slope of the curve (B/) I) can be displayed.
It is now possible to detect magnetic permeability μ from .

When measuring the magnetic permeability of a magnetic shielding material, etc. using the magnetic permeability measuring device configured as described above, the opening side end surface of the high-rigidity support material 1 is brought into contact with the object to be measured 6, and the current value of the electromagnet 3 is If a corresponding magnetic field is supplied to the electromagnet 3 and the object to be measured 6
occurs between Further, a magnetic flux density proportional to the magnetic permeability of the object to be measured 6 is generated in the magnetic field of the electromagnet 3, and the electromagnet 3 is attracted to the object to be measured by Coulomb force, causing strain in the elastic body 2.

Therefore, the current value from the A/D converter IO and the detected strain value from the strain gauge 4 are input to the converter 5, where they are converted into a magnetic field (H) and a magnetic flux density (B). In addition, the current value supplied to the electromagnet 3 is changed and swept by the current control device 9, and the magnetic field (H) and magnetic flux density (B) are continuously measured by the converter 5 to form a continuous -H curve. is displayed on the converter 5 in nominal time, and the magnetic permeability μ is calculated from the gradient (B/H) of the curve.

Although the magnetic permeability measuring device described above uses an electromagnet, a permanent magnet may be used instead to detect the magnetic flux soundness of the object to be measured, or several types of permanent magnets with different magnetic forces may be used as an elastic body. 2 may be made detachable so that the magnet can be replaced and the magnetic field (1-1) can be changed so that the magnetic permeability can be measured in the same manner as described above.

[Effects of the Invention] According to the magnetic permeability measuring device or measuring system of the present invention, there is no need to cut out a ring sample from the object to be measured, so magnetic permeability at various points can be easily measured, and moreover, it is possible to easily measure the magnetic permeability of various points. The magnetic permeability can be measured at various times, such as when the factory processing is completed, when it is delivered to the site, and when the installation is completed, and the actual magnetic permeability can be measured and understood.

Also, when constructing magnetic shielding walls around the MRI room using magnetic shielding materials, do not use materials with excessive safety factors (materials with realistic values can be used, and the magnetic shielding materials can be installed). If the predetermined magnetic permeability is not secured after that, it is easy to take measures such as increasing the number of layers since the building has not yet been finished.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the magnetic permeability measuring device of the present invention, Fig. 2 is a system diagram of the device, and Fig. 3 is an explanation showing the B-8 curve of a material magnetically annealed by a conventional method and a sample as processed. It is a diagram. l; High rigidity support material 2; Elastic body

Claims (3)

[Claims] (1) Attach an electromagnet to the high-rigidity support material that comes into contact with the object to be measured through an elastic body so as to face the measurement surface, attach a strain gauge to the elastic body, and connect the detected value of the strain gauge to the electromagnet. What is claimed is: 1. A magnetic permeability measuring device comprising a converter for measuring magnetic permeability of an object to be measured based on an input current value. (2) The magnetic permeability measuring device according to claim 1, wherein a DC power source is connected to the coil of the electromagnet via a current control device. (3) Using the magnetic permeability measuring device according to claim (1) or (2), the magnetic field (H) and magnetic flux density (B) are converted by a converter by sweeping the input current value to the electromagnet. 1. A magnetic permeability measurement system that measures and detects a continuous B-H curve in real time, and determines magnetic permeability based on the B-H curve.