JP5881532B2 - Noise filter for shielded cable - Google Patents

Description

  The present invention relates to a noise filter for a shielded cable that suppresses propagation of electromagnetic noise superimposed on the shielded cable by being loaded on the shielded cable.

  In a communication system or the like in an environment with a lot of electromagnetic noise, a shielded cable is used to electromagnetically isolate it from the outside or suppress electromagnetic interference radiation from the cable. The shielded cable is composed of an inner conductor wire, an outer shield outer conductor (outer conductor sheath), and a holding resin. Then, the signal system of the communication system is connected to the internal conductor line, and the outer conductor sheath is connected to the ground, thereby forming a shield structure that wraps the internal signal system with the ground.

  However, in high-powered equipment that handles high power, the ground that is the return path of the large current and the ground of the weak-electrical conductor wire are often separated from each other, and each ground is separated. . In the following, a metal casing or the like serving as a ground for the return path of the strong electric system is referred to as a frame ground (FG), and a signal ground connected to the outer conductor of the shielded cable is referred to as a signal ground (SG). In the high-voltage equipment, since the FG system and the SG system are separated, if electromagnetic noise is superimposed on the SG, it is transmitted through the outer conductor of the shielded cable and may affect various devices. .

Therefore, conventionally, a configuration that suppresses only the electromagnetic noise of the SG system is known (see, for example, Patent Documents 1-4). In the noise filter disclosed in Patent Document 1, a conductive material is used for the fixing holder case in which the split magnetic core is accommodated, and the fixing holder case has a shielding characteristic. Then, by attaching this noise filter to a shielded cable from which the shielding outer conductor is removed, a magnetic filter is formed in the shielded cable to suppress noise propagation.
Further, in the noise filter disclosed in Patent Document 2, an inductor (L) formed by spirally winding a thin conductor around a cylindrical body, and another conductor is provided at an opposing position inside or outside the cylindrical body. By combining a capacitor (C) formed between the conductors, a function as an LC filter is provided.

Moreover, in the noise filter disclosed in Patent Document 3, a magnetic filter is formed by arranging a cylindrical magnetic body formed by mixing a magnetic material and a resin and a normal conductor on a cable in an annual ring shape. Is forming.
Furthermore, in the contact pin with a noise filter disclosed in Patent Document 4, the inner electrode of the feedthrough capacitor is connected to the outer conductor of the contact pin, and the outer electrode of the feedthrough capacitor is connected to the common electrode of the circuit board. Noise that propagates through the conductor is suppressed.

Japanese Patent Laid-Open No. 06-310340 Japanese Patent Laid-Open No. 02-238705 Japanese Patent Laid-Open No. 03-21906 Japanese Patent Laid-Open No. 07-073935

However, in patent documents 1 and 3, only a magnetic body is used as a component of a noise filter. Therefore, there is a problem that the filter effect cannot be sufficiently obtained depending on the frequency of noise to be filtered.
Further, Patent Document 2 does not aim to use a cable inserted into a cylinder having an LC filter function. Therefore, when loading a filter on a shielded cable, the shielded cable must be cut to expose the core wire (conductor wire), and then the core wire and the filter must be connected, making it difficult to load at any position. was there.
Furthermore, patent document 4 is a structure which loads a filter in the specific position which arrange | positions a contact pin. Therefore, there is a problem that the filter cannot be loaded at an arbitrary position on the shielded cable.

  The present invention has been made to solve the above-described problems, and is applicable to various types of shielded cables, and shielded cable noise that suppresses propagation of electromagnetic noise at an arbitrary position on the shielded cable. The purpose is to provide a filter.

The noise filter for shielded cable according to the present invention includes an inductive internal filter composed of a semi-cylindrical inductive member divided into two along the axial direction, and a semi-cylindrical filter divided into two along the axial direction. It is configured by combining a capacitive internal filter formed by attaching a capacitive member to the inner side surface of the conductive cylinder, and has an internal filter unit loaded on a shielded cable and has electrical conductivity. An external cylinder that is housed in a connected state, and an electrical connection portion that is electrically conductive and electrically connects the external cylinder to an external conductor.

  According to the present invention, since it is configured as described above, the internal filter unit that is structurally and electrically fixed by the outer cylinder can be combined and arranged, and the filter necessary for various electromagnetic noises to be suppressed. A noise filter having characteristics can be loaded at an arbitrary position of the shielded cable. As a result, propagation of electromagnetic noise superimposed on the outer conductor of the shielded cable can be suppressed.

It is a perspective view which shows the structure of the noise filter which concerns on Embodiment 1 of this invention. It is a perspective view which shows the structure of the external cylinder in Embodiment 1 of this invention. It is a perspective view which shows the structure of the inductive internal filter in Embodiment 1 of this invention. It is a perspective view which shows the structure of the capacitive internal filter in Embodiment 1 of this invention. It is a perspective view explaining the operation | movement at the time of loading the noise filter which concerns on Embodiment 1 of this invention on a shield cable. It is an equivalent circuit diagram (π-type filter) of the noise filter according to the first embodiment of the present invention. It is a figure which shows the comparison of the propagation cut-off characteristic of (pi) type | mold filter, inductor filter, and capacitor | condenser filter in Embodiment 1 of this invention. It is an equivalent circuit diagram (T-type filter) of the noise filter according to the first embodiment of the present invention. It is an equivalent circuit diagram (LC filter) of the noise filter according to the first embodiment of the present invention. It is an equivalent circuit diagram (CL filter) of the noise filter according to the first embodiment of the present invention. It is a figure which shows the comparison of the propagation | transmission cutoff characteristic of the pi type filter, T type filter, LC filter, CL filter, inductor filter, and capacitor | condenser filter in Embodiment 1 of this invention. It is a figure which shows the noise propagation suppression amount with respect to the circuit constant of the inductive internal filter and capacitive internal filter in Embodiment 1 of this invention for every step number. It is a figure which shows the parameter regarding adjustment of the circuit constant of the inductive internal filter in Embodiment 1 of this invention. It is a figure which shows the parameter regarding adjustment of the circuit constant of the capacitive internal filter in Embodiment 1 of this invention. It is a perspective view which shows the structure of the external cylinder in Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a perspective view showing the configuration of a shielded cable noise filter 1 according to Embodiment 1 of the present invention.
The shielded cable noise filter 1 (hereinafter referred to as the noise filter 1) is mounted on the shielded cable 10 and suppresses propagation of electromagnetic noise superimposed on the shielded cable 10. As shown in FIG. 1, the noise filter 1 includes a cylindrical outer tube 2 that can be opened and closed along the axial direction, and a state in which the noise filter 1 is electrically connected to the outer tube 2 after being loaded on the shield cable 10. It is comprised from the internal filter unit 3 accommodated in.
The internal filter unit 3 is configured by combining a split-type inductive internal filter 4 and a split-type capacitive internal filter 5. Further, both outer end portions of the outer cylinder 2 are fixed to a pedestal (electrical connection portion) 6, and the pedestal 6 is fixed to a casing (external conductor) of an electronic device (not shown).

Next, the configuration of the outer cylinder 2 will be described with reference to FIG.
As shown in FIG. 2, the outer cylinder 2 includes a lower outer cylinder 21 and an upper outer cylinder 22 that are made of a conductor and are divided into two along the axial direction. An opening / closing mechanism 23 such as a hinge for opening and closing the other side is provided at one joint portion of the lower outer cylinder 21 and the upper outer cylinder 22. Further, a fixing stopper 24 for fixing the closed upper and lower outer cylinders 21 and 22 is provided at the other joint portion.

The pedestal 6 is made of a conductor, and functions as a receiving portion that matches the shape of the outer cylinder 2 and as a connecting portion for fixing to the housing of the electronic device. The pedestal 6 electrically connects the outer cylinder 2 and the housing of the electronic device. At this time, for example, an electrical connection is realized by attaching a conductive adhesive or tape to the base 6 and fixing it to the housing.
The electrical connecting portion may be configured other than the illustrated pedestal 6 as long as it can hold the outer cylinder 2 and can be electrically connected to the casing of the electronic device. Alternatively, the outer cylinder 2 may be directly fixed to the casing of the electronic device using a conductive adhesive.

Next, the configuration of the internal filter unit 3 (inductive internal filter 4 and capacitive internal filter 5) will be described with reference to FIGS.
As shown in FIG. 3, the inductive internal filter 4 includes a semi-cylindrical lower filter cylinder 41 and an upper filter cylinder 42 that are divided into two along the axial direction. An opening / closing mechanism (not shown) for opening and closing the other side is provided at one joint portion of the lower filter cylinder 41 and the upper filter cylinder 42.
The inductive internal filter 4 is composed of a magnetic material (inductive member) 43 such as ferrite. Further, the outer diameter of the inductive inner filter 4 is substantially the same as the inner diameter of the outer cylinder 2, and is configured so that the closed inductive inner filter 4 can be accommodated in the outer cylinder 2 in an electrically connected state. ing. Further, the inner diameter of the inductive internal filter 4 is configured to have a dimension corresponding to the wire diameter of the shielded cable 10 to be loaded.

On the other hand, as shown in FIG. 4, the capacitive internal filter 5 includes a semi-cylindrical lower filter cylinder 51 and an upper filter cylinder 52 that are divided into two along the axial direction. An opening / closing mechanism (not shown) that opens and closes the other side is provided at one joint of the lower filter cylinder 51 and the upper filter cylinder 52.
The capacitive internal filter 5 includes a conductor cylinder 53 and a capacitive member such as a dielectric 54 attached to the inner surface of the conductor cylinder 53. The outer diameter of the capacitive internal filter 5 is substantially the same as the inner diameter of the outer cylinder 2, and is configured so that the closed capacitive inner filter 5 can be accommodated in a state where it is electrically connected to the outer cylinder 2. ing. Moreover, the internal diameter of the capacitive internal filter 5 is comprised by the dimension according to the wire diameter of the shielded cable 10 loaded.

Next, an example of a method for loading the noise filter 1 configured as described above onto the shielded cable 10 will be described with reference to FIG.
The shielded cable 10 is provided with an insulating covering material, an outer conductor 101 provided inside the insulating covering material to connect the SG system of the electronic device, and a signal cable of the electronic device provided inside the outer conductor 101. Conductor wire (signal line 102).

  When loading the noise filter 1 on the shielded cable 10, first, as shown in FIG. 5, first, the internal filter unit 3 is opened up and down, and the shielded cable 10 is moved upward so as to fit in the internal space of the lower filter cylinders 41 and 51. Insert from and fix. Subsequently, the upper filter cylinders 42 and 52 are closed, and the internal filter unit 3 is loaded on the shielded cable 10.

Next, the shielded cable 10 loaded with the internal filter unit 3 is placed in the lower external cylinder 21 with its position aligned so that the outer surface of the internal filter unit 3 contacts the inner surface of the outer cylinder 2. FIG. 5 shows a case where the internal filter unit 3 is housed in the external tube 2 before being loaded onto the shielded cable 10.
Subsequently, the upper outer cylinder 22 is closed, and the upper and lower outer cylinders 21 and 22 are fixed by the opening / closing mechanism 23 and the fixing stopper 24. Thereafter, a conductive adhesive or tape is attached to the base 6 and fixed to the casing of the electronic device.
Thereby, the conductor cylinder 53, the outer cylinder 2, the base 6, and the housing of the electronic device of the capacitive internal filter 5 are in an electrically connected state.

  The noise filter 1 loaded on the shielded cable 10 causes the electromagnetic noise superimposed on the outer conductor 101 of the shielded cable 10 to be applied to the dielectric 54 of the capacitive inner filter 5, the conductor cylinder 53 of the capacitive inner filter 5, and the outer cylinder. 2 and the pedestal 6 to function as a ground to the housing (FG) of the electronic device. That is, the SG system and the FG system are equivalently connected.

On the other hand, noise propagation suppression due to the properties of the magnetic body 43 can be synthesized by loading the shielded cable 10 together with the inductive internal filter 4.
For example, when the internal filter unit 3 composed of the filters 4 and 5 arranged in the order of capacitive, inductive, and capacitive is loaded on the shielded cable 10, an equivalent capacitor to the outer conductor 101 of the shielded cable 10. And the same effect as the case where the circuit element of an inductor is inserted can be acquired. In this case, the noise filter 1 becomes an equivalent circuit as shown in FIG. 6, and a π-type LC filter can be formed.

  FIG. 7 shows a comparative example of propagation cut-off characteristics using a π-type filter, an inductor filter, and a capacitor filter. As shown in FIG. 7, in the band where the frequency of the target electromagnetic noise is higher than F in FIG. 7, the propagation suppression effect by the π-type filter is higher than that of the inductor filter and the capacitor filter. That is, it can be seen that the π-type filter is effective for electromagnetic noise whose frequency component is biased toward the high frequency side.

In FIG. 7, the π-type filter is described as an example, but the filter configuration in the present invention is not limited to this. For example, a T-type filter (FIG. 8) in which the filters 4 and 5 are arranged in the order of inductive, capacitive, and inductive, an LC filter (FIG. 9) and a CL filter (FIG. 10) using the filters 4 and 5 one by one. ) Or the like.
Also in this case, as shown in FIG. 11, it can be seen that the propagation suppression amount is larger in the high frequency band than the inductor filter and the capacitor filter. Note that the propagation suppression amounts of the LC filter and the CL filter shown in FIG. 11 show the case where the C and L circuit constants are the same.

Next, the difference in the amount of propagation suppression due to the filter configuration will be described.
First, in FIG. 11, focusing on the drop in the amount of propagation suppression with respect to frequency in each filter configuration, a first stage filter (inductor filter or capacitor filter), a second stage filter (LC filter or CL filter), a third stage filter (π-type filter) It can be seen that the number increases in the order of (and T-type filter). That is, it can be seen that the propagation suppression amount can be increased by increasing the number of stages of the filter configuration.

  Further, the propagation suppression amount varies depending on the circuit constants of the filters 4 and 5. FIG. 12 is a diagram showing the amount of propagation suppression for the circuit constants of the filters 4 and 5 (elements) for each number of stages. From FIG. 12, it can be seen that the propagation suppression amount decreases as the circuit constant increases. The circuit constants can be adjusted by changing the properties of the materials constituting the filters 4 and 5 and the dimensions such as the width and diameter of the filters 4 and 5. Hereinafter, a method for adjusting the circuit constants of the filters 4 and 5 will be described.

First, FIG. 13 shows parameters related to adjustment of circuit constants of the inductive internal filter 4. 13A shows the inductive internal filter 4 having the same shape as that in FIG. 3, and FIG. 13B shows the inductive internal filter 4 in which the thickness of the magnetic body 43 is changed. In FIG. 13, a _L is the inner radius of the cylinder of the magnetic body 43, b _L is the outer radius of the cylinder of the magnetic body 43, d _L is the width of the cylinder of the dielectric 43, and μr is the magnetic body. The relative permeability of 43.
On the other hand, the value of the self-inductance L of the inductor is generally expressed by the following equation where the vacuum permeability is μ0, the width of the magnetic cylinder is W, the inner radius of the magnetic cylinder is Rin, and the outer radius is Rout. The

When this is applied to the inductive internal filter 4 shown in FIG. 13A, the cylinder width is W = d _L , the inner radius of the cylinder of the magnetic body 43 is Rin = a _L , and the outer radius is Rout = b _L. It becomes. On the other hand, when applied to the inductive internal filter 4 shown in FIG. 13B, the area inside the cylinder of the magnetic body 43 is S = 2πa _L '× d _L and the thickness of the magnetic body is d = b _L ' -a. _L '. Therefore, for example, if the thickness of the magnetic body 43 of the inductive internal filter 4 in FIG. 13B is increased by 4 times that of the inductive internal filter 4 in FIG. 13A, the self-inductance is increased by ln (4) times. It can be seen from equation (1). Similarly, when the width of the magnetic body 43 is increased four times, the self-inductance is increased four times. Further, when a magnetic material 43 having a relative permeability twice as large is used, the self-inductance is doubled.

Next, FIG. 14 shows parameters related to adjustment of circuit constants of the capacitive internal filter 5. 14A shows the capacitive internal filter 5 having the same shape as that in FIG. 4, and FIG. 14B shows the capacitive internal filter 5 in which the thickness of the dielectric 54 is changed. In FIG. 14, a _C is the inner radius of the cylinder of the dielectric 54, b _C is the outer radius of the cylinder of the dielectric 54, d _C is the width of the cylinder of the dielectric 54, and εr is the dielectric. The relative dielectric constant is 54.
On the other hand, the value of the capacitance C of the capacitor is generally expressed by the following equation where ε0 is the dielectric constant of vacuum, S is the area of the opposing conductor plate, and d is the interval between the opposing conductor plates.
C = ε0 × εr × (S / d) (2)

When this is applied to the capacitive internal filter 5 shown in FIG. 14A, the area inside the cylinder is S = 2πa _C × d _C with respect to the inner radius a _C of the cylinder of the dielectric 54. The thickness of 54 is d = b _C −a _C. On the other hand, when applied to the capacitive internal filter 5 shown in FIG. 14B, the area inside the cylinder of the dielectric 54 is S = 2πa _C '× d _C , and the thickness of the dielectric 54 is d = b _C ' −. a _C '. Therefore, for example, when the thickness of the dielectric 54 of the capacitive internal filter 5 in FIG. 14B is increased by a factor of 4 with respect to the capacitive internal filter 5 in FIG. 14A, the capacitance becomes ¼. This can be seen from equation (2). Similarly, increasing the width of the dielectric 54 by a factor of four increases the capacitance by a factor of four. Further, when a dielectric 54 having a relative dielectric constant that is twice as large is used, the capacitance is doubled.

  From the above, it is possible to obtain a desired propagation suppression amount by changing the number of stages of the filters 4 and 5, their arrangement, and circuit constants.

  As described above, according to the first embodiment, the divided inductive internal filter 4 made of the magnetic material 43 and the divided capacitive internal filter 5 made of the dielectric material 54 are combined and loaded on the shielded cable 10. The internal filter unit 3 is electrically conductive, the external cylinder 2 is electrically conductive, and the internal filter unit 3 is stored in an electrically connected state, and is electrically conductive, and the external cylinder 2 is electrically connected to the casing of the electronic device. Therefore, the noise filter 1 against various electromagnetic noises can be loaded at an arbitrary position of the shielded cable 10. As a result, propagation of electromagnetic noise superimposed on the outer conductor 101 of the shielded cable 10 can be suppressed.

  Note that the outer tube 2 and the inner filter unit 3 of the noise filter 1 according to the first embodiment can be made with various diameters according to the wire diameter of the shielded cable 10. Thereby, the noise filter 1 can be loaded with various types of shielded cables 10, and the expandability of the noise filter 1 can be improved.

Embodiment 2. FIG.
In the second embodiment, in the noise filter 1 shown in the first embodiment, the outer cylinder 2 is changed to the outer cylinder 2b. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and the description thereof is omitted.

FIG. 15 is a perspective view showing the configuration of the outer cylinder 2b according to the second embodiment of the present invention.
As shown in FIG. 15, the outer cylinder 2 b includes a cylindrical insulator 25, a first conductive material 26 disposed on the inner surface of the insulator 25, and both outer end portions facing the pedestal 6 of the insulator 25. And a second conductive material 27 electrically connected to the first conductive material 26.
An opening / closing mechanism 23 such as a hinge for opening and closing the other side is provided at one joint portion of the lower outer cylinder 21 and the upper outer cylinder 22. Further, a fixing stopper 24 for fixing the closed upper and lower outer cylinders 21 and 22 is provided at the other joint portion.

  The pedestal 6 is disposed at a position in contact with the second conductive material 27 at both outer end portions of the outer cylinder 2b. Therefore, the structure of the outer cylinder 2b according to the present embodiment causes the inner surface of the outer cylinder 2b. The first conductive material 26 and the pedestal 6 are electrically connected. Therefore, the first conductive material 26 disposed on the inner surface of the outer cylinder 2b can be grounded at both outer end portions of the outer cylinder 2b.

Next, a method for loading the outer cylinder 2b configured as described above onto the shielded cable 10 loaded with the inner filter unit 3 will be described.
First, the shielded cable 10 loaded with the internal filter unit 3 is placed in the lower external cylinder 21 with its position aligned so that the outer surface of the internal filter unit 3 is in contact with the inner surface of the outer cylinder 2b. Subsequently, the upper outer cylinder 22 is closed, and the upper and lower outer cylinders 21 and 22 are fixed by the opening / closing mechanism 23 and the fixing stopper 24. Thereafter, a conductive adhesive or tape is attached to the base 6 and fixed to the casing of the electronic device.
As a result, the conductive cylinder 53 of the capacitive internal filter 5, the first conductive material 26 on the inner surface of the outer cylinder 2b, the second conductive material 27 at both outer ends of the outer cylinder 2b, the pedestal 6, and the housing of the electronic device Are in an electrically connected state.

  The noise filter 1 loaded on the shielded cable 10 causes the electromagnetic noise superimposed on the outer conductor 101 of the shielded cable 10 to be applied to the dielectric 54 of the capacitive inner filter 5, the conductor cylinder 53 of the capacitive inner filter 5, and the outer cylinder. It functions to ground to the housing (FG) of the electronic device via 2b and the pedestal 6. That is, even if the entire outer cylinder 2b is not made of a conductor, a function equivalent to that of the first embodiment can be realized.

  As described above, according to the second embodiment, the outer cylinder 2b is made up of the cylindrical insulator 25, the first conductive material 26 disposed on the inner surface of the insulator 25, and the base of the insulator 25. The same effect as that of the first embodiment can be obtained even if the second conductive material 27 is disposed on the outer portion in contact with the first conductive material 26 and electrically connected to the first conductive material 26.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  1 Noise filter for shield cable, 2, 2b External cylinder, 3 Internal filter unit, 4 Inductive internal filter, 5 Capacitive internal filter, 6 Base (electrical connection part), 10 Shield cable, 21 Lower external cylinder, 22 Upper external Tube, 23 Opening / closing mechanism, 24 Fixed stopper, 25 Insulator, 26, 27 First and second conductive materials, 41, 51 Lower filter tube, 42, 52 Upper filter tube, 43 Magnetic body (inductive member), 53 Conductor Cylinder, 54 dielectric (capacitive member), 101 outer conductor, 102 signal line.

Claims (3)

In a shielded cable noise filter that suppresses propagation of electromagnetic noise superimposed on the shielded cable by being loaded on the shielded cable,
An inductive internal filter consisting of a semi-cylindrical inductive member divided into two along the axial direction and a semi-cylindrical filter divided into two along the axial direction, and capacitive on the inner surface of the conductive cylinder An internal filter unit configured by combining a capacitive internal filter formed by pasting members and loaded on the shielded cable;
An external cylinder having conductivity and storing the internal filter unit in an electrically connected state;
A noise filter for a shielded cable, comprising: an electrical connection portion that is electrically conductive and electrically connects the outer tube to an external conductor. The internal filter unit, said inductive filter interior, the capacitive internal filter, according to claim 1 shield noise filter cable according to characterized in that it is arranged in order of the inductive filter interior. The outer cylinder is
A tubular insulator;
A first conductive material disposed on an inner surface of the insulator;
The second conductive material is disposed on an outer portion of the insulator that is in contact with the electrical connection portion, and is electrically connected to the first conductive material. The noise filter for shielded cable described.

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