JP3084241B2 - Noise reduction device for transmission media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for a transmission medium having a coaxial structure, and more particularly to a noise reduction device which receives electromagnetic interference from an environment when a transmission medium having a coaxial structure is branched and used. The present invention relates to a transmission medium noise reduction device for reducing noise.

[0002]

2. Description of the Related Art Generally, a communication area of a client-server type data communication system is a bus type local area network (hereinafter abbreviated as LAN) in which a plurality of stations share one transmission line. JIS X 5252 standard LAN is frequently used. Each station connected to the JIS X5252 standard LAN is a CSMA / CD (Carrier Sense Multipl
Data transmission is performed using an access method called e Access with Collision Detection). The general operation of this access method will be described below.

(1) A station that transmits a frame (an information block in which transmission destination data, a destination address, a source address, an error check redundant bit, etc. are added) is transmitted when all other stations are not transmitting. Wait for.

(2) A frame is transmitted to a transmission line in a bit serial form. During transmission, it monitors whether there is a collision with a frame transmitted by another station.

(3) When a collision is detected, the transmission is immediately terminated, and then a signal is transmitted to all other stations for surely transmitting the occurrence of the collision.

(4) After waiting for a random time, transmission is attempted again from item number (1).

The outline of the data receiving operation of each station is shown below.

(1) Wait for reception of a frame to be completed.

(2) If a collision frame is detected (according to item number (3) of the transmission operation), the frame is discarded and the process returns to item number (1).

(3) Check whether the received frame is a frame addressed to the own station. If the frame is not addressed to the own station, the frame is discarded, and the process returns to item number (1).

(4) The normality of the received data is checked by an error check or the like.

Next, physical specifications of the JIS X 5252 standard LAN will be described. According to the JIS X 5252 standard, the average bit error rate in the physical layer
In ^1-8 below, in order to provide a physical communication means the transmission speed has a performance of 10 Mbit / s with respect to each station, 10BAS
It defines a baseband coaxial system called E5 format (a system that directly encodes and outputs information on a transmission medium using a coaxial cable).

An example of the configuration of the baseband coaxial system is shown in FIG. 2 (refer to FIG. 8.11 of JIS X 5252). In this system, as shown, one coaxial cable 1 terminated at both ends with terminators 4 having matching characteristic impedances forms one cable segment. Maximum length of one cable segment is 500m
It is. One cable segment has a medium connection unit (hereinafter referred to as M) for connecting a station that performs data communication.
AU) 5 can be connected up to 100 units.
A data terminal device (hereinafter abbreviated as DTE) 3 of a station that performs data communication is connected to the MAU 5 via an attachment unit interface (hereinafter abbreviated as AUI) cable 2 having a maximum cable length of 50 m. Although not shown, another cable segment or link segment (a point-to-point with a repeater set at both ends) is provided by a repeater set provided at any one of the MAU5 positions shown in FIG. Connection coaxial cable)
, The line length of the coaxial cable between any MAUs in one system can be extended up to a maximum of 2.5 km.

The MAU 5 is provided with an AUI connector for connecting to the AUI cable 2 and a coaxial tap connector for connecting to the coaxial cable 1, and has a shielded enclosure containing a circuit for electrical connection. And In order to control the connection between the DTE 3 and the coaxial cable 1, the MAU 5 transmits (1) a serial data bit string to the medium (coaxial cable 1), and (2) a medium (coaxial cable 1). And (3) a collision detection function that detects that two or more stations are transmitting at the same time.
(4) It has four functions, a Java function that automatically interrupts the transmission function and prohibits the output of an abnormally long data string.

[0015] Such MAU5 is designed on the premise of the following.

(A) The DTE 3 is used by properly grounding.

(B) The shield of the coaxial cable 1 is grounded by a single point grounding method.

(C) The AUI cable 2 is composed of four sets of individually shielded strands and an overall shield covering them, and the overall shield is connected to the MAU5 and DTE3 shielded enclosures via the AUI connector shell. Connected.

The MAU 5 includes the coaxial cable 1 and the AU
The I cable 2 is electrically insulated. The insulation impedance is not less than 250 kΩ at 60 Hz and not more than 15 Ω from 3 MHz to 30 MHz. In addition, the specification of 3 MHz to 30 MHz specifies that when the MAU5 receives transient electromagnetic interference, the energy is transferred to the entire shield of the AUI and the DAU.
This is a specification for bypassing to the ground through the grounding of the TE.

In connection between the MAU 5 and the coaxial cable 1, the length of the lead from the coaxial cable 1 must be minimized so as not to deteriorate the transmission characteristics of the cable. According to the JIS X 5252 standard, if the length of the lead wire is 30 mm or more, the required specifications of the system cannot be satisfied. For this reason, the MAU 5 and the connecting device of the coaxial cable 1 usually have an integral structure.

The JIS X 5252 standard specifies a drilled coaxial tap connector system which does not require cutting the coaxial cable, as one of the methods for connecting the MAU 5 and the coaxial cable 1. This method is widely used because it is excellent in easiness of construction work and flexibility in changing a network (addition or relocation of a station).

MAU5 by coaxial tap connector
Is attached to the coaxial cable 1 as shown in FIG.
"Conceptual diagram of coaxial tap connector" in Figure 8.8 of IS X 5252) and Figure 3 (b) (Figure of JIS X 5252)
As shown in “Typical coaxial tap connector circuit” in Section 8.9), for example, the following procedure is used.

(1) The tap blocks 5a and 5b are attached to the coaxial cable 1.

(2) The shield structure 103 is penetrated through the outer sheath 102 of the coaxial cable 1 and bites into the shield structure 103, and the shield contact 5e that is in electrical contact with the shield structure 103 is attached. (3) Using the tapping screw 5d, a hole 106 that penetrates through the outer cover 102, the shield structure 103, and the insulating layer 104 of the coaxial cable 1 and reaches the center conductor 105 is formed.
A signal contact 5f that is in electrical contact with the center conductor 105 is attached through the hole 106.

(4) The M accommodated in the connector housing 50 having a shielding performance of 40 dB or more at 50 MHz.
An electronic circuit board (not shown) of the AU5 is attached to the tap block 5a. At this time, the signal contact 5f and the shield contact 5e are respectively connected to the signal line terminal 5h and the return line terminal 5g that reach the active circuit of the MAU5.

[0026]

In a data communication system using a LAN using the MAU configured as described above, hardware forming a physical channel of the LAN is composed of an electromagnetic field, an electrostatic discharge, and a connection between ground points. Must withstand electromagnetic interference from the environment, such as temporary fluctuations in potential. The interference levels that this hardware must withstand, for example, according to the JIS X 5252 standard, are as follows.

(1) The electric field strength of the surrounding plane wave is
2V / m, 30M from 0kHz to 30MHz
5 V / m from Hz to 1 GHz. The electric field strength is a typical value at a point 1 km away from the broadcasting station.

(2) An interference voltage having an instantaneous slope of 1 V / ns between the shield of the coaxial cable and the ground point of the DTE. In addition,
This interference voltage has, for example, an internal impedance of a signal source of 50Ω, a peak value of 15.8 V, and a frequency of 10 MHz.
This corresponds to the case where a sine wave of z is applied.

However, the LA constructed as described above
When the N system is operated, the following phenomena, the cause of which is not well understood, are observed in many systems.

(1) A phenomenon that the throughput of the LAN is lower than usual often occurs.

(2) The device connected to the LAN stops operating (for example, a personal computer (PC: Persona)
l) Keyboard input and mouse operation of computer) suddenly become impossible.

(3) The MAU breaks down within an operation time considerably shorter than the design reliability of the MAU. These phenomena are
According to a study by the present inventors, a metal double floor for installing a computer (hereinafter, referred to as a free access floor) and a metal double floor for an office (hereinafter, referred to as an OA floor) are provided under the floor. It was found that LAN coaxial cables and MAUs were laid, and those floors tended to be used in places where the service life of the floors was more than several years. The basic structure of the free access floor and the OA floor is the same (support legs that support the floor panel are arranged in a lattice on the original floor surface, and metal floor panels are spread over it, To form a double bed).

The cause has not been clarified conventionally. However, the present inventors have found that the MAU using the conventional coaxial tap / connector system has insufficient resistance to interference by transient electromagnetic waves radiated due to electrostatic discharge. As a result of research, it has been found that noise is liable to be superimposed on signal contacts and shield contacts drawn out of the device, and as a result, various obstacles are caused.

That is, as shown in FIG. 3 (b), the signal contact 5f which makes electrical contact with the center conductor 105 through the hole 106 which penetrates the outer sheath 102, the shield structure 103 and the insulating layer 104 of the coaxial cable 1 respectively. It is considered that noise is injected into the center conductor of the coaxial cable by the following two actions.

(1) At the portion of the hole formed in the shield structure 103, since the uniformity of the conductor is lost, a turbulent magnetic field is generated around the conductor. At this time, a noise voltage due to a mutual induction action is induced in the conductor portion of the signal contact 5f, and the induced noise voltage is injected into the center conductor 105.

(2) The periphery of the hole formed in the shield structure 103 and the conductor of the signal contact 5f are electrostatically coupled. Around the hole formed in the shield structure 103, the impedance sharply increases, so that a part of the noise current flowing through the skin of the shield structure flows into the center conductor 105 by the above-described electrostatic coupling.

An object of the present invention is to provide a transmission medium noise reduction apparatus for reducing noise due to electromagnetic interference such as transient electromagnetic waves radiated by electrostatic discharge when a coaxial transmission medium is branched and used. Is to do.

[0038]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a transmission medium having a coaxial structure having a center conductor, an insulating layer, a shield structure, and an outer sheath. And a shield tap connector adjacent to the branch of the transmission medium and electrically connected to a shield structure of the transmission medium, and a shield tap connector adjacent to the branch of the transmission medium and inserted into the transmission medium. An inductance element to be connected, a conductive ground plate, the conductive ground plate, and a plurality of connection lines for electrically connecting the shield tap connector, wherein the shield tap connector has a plurality of connection lines. A connection terminal connected to the connection line and electrically connected to a shield structure of the transmission medium; Further, the ground plate includes a plurality of terminals for connecting the plurality of connection lines, respectively.

In this case, the shield tap connector is electrically connected to the shield structure of the transmission medium, and the connection terminals of the shield tap connector and the plurality of terminals of the ground plate are respectively connected by a plurality of connection wires. . On the other hand, the ground plate is laid in close contact with the floor of the building at the time of construction, that is, a concrete floor surface covering a conductive structure such as a steel frame of the building. The ground plane itself and
It can be regarded as an aggregate of micro capacitors generated between the building and the conductive structure that can be considered equivalent to the earth,
The noise current is bypassed to ground via the inductance element. For this reason, noise can be reduced.

[0040]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a noise reduction device according to an embodiment of the present invention.

As shown in FIG. 1, the embodiment of the present invention provides a noise reduction device in a coaxial cable when a coaxial cable is branched and used.

In FIG. 1, the noise reduction device is adjacent to the MAU 5 of the branch connector for branching the coaxial cable 1, and is adjacent to the shield tap connector electrically connected to the shield structure of the coaxial cable 1, and adjacent to the MAU 5. A ferrite core 300 of an inductance element inserted and connected to the coaxial cable 1, and a conductive high-frequency grounding device 400.
And The shield tap connector has a connection terminal 411 for electrically connecting the high-frequency grounding device 400 and the shield structure of the coaxial cable 1 by a plurality of connection wires 402.
The high-frequency grounding device 400 includes a plurality of connection lines 402
Are connected to each other.

As shown in FIG. 1, the ferrite core 300 is attached to the coaxial cable 1 so as to be close to both ends of the tap blocks 5a and 5b of the MAU 5. At least one ferrite core 300 is provided, and the tap blocks 5a and 5
b, or at least one of both ends where the MAU 5 and the shield tap connector 410 are mounted.

The ferrite core 300 is, for example, a split type divided into two blocks, and has a through hole through which a coaxial cable is inserted when the two blocks are connected. That is, the two blocks are connected by sandwiching the coaxial cable, and each block is provided with a recess corresponding to the outer periphery of the coaxial cable in a portion that contacts the coaxial cable. Therefore, it is not necessary to cut the coaxial cable.
Since the two blocks are connected and connected, one of the blocks has a concave portion (not shown) and the other has a convex portion (not shown). These concave portions and convex portions are connected by being engaged with each other. Center conductor 10 of coaxial cable 1
5 (see FIG. 3) is proportional to the noise current flowing through the shield structure. Therefore, adding the ferrite core 300 prevents the noise flowing through the shield structure of the coaxial cable. And thereby the center conductor 105 of the coaxial cable 1 (see FIG. 3).
Can be attenuated. The ferrite core used has, for example, an insertion impedance of 5
The one having about 100Ω at 0 MHz is used.

FIG. 5 shows a configuration diagram of the shield tap connector 410. In FIG. 5, a shield tap connector 410 is electrically connected to a shield structure of a coaxial cable. The shield tap connector 410 is provided with a connection terminal 411 for connecting a connection line. The shield tap connector 410 is composed of, for example, two blocks 410a and 410b. Each block 4
Each of 10a and 10b has a recess corresponding to the outer circumference of the coaxial cable so that the coaxial cable can be sandwiched between the portions. A metal blade terminal 413 is attached to a surface of one of the blocks in contact with the outer periphery of the coaxial cable. The two blocks sandwich the coaxial cable and are tightened by tightening bolts 412. At this time, the tip of the blade terminal 413 penetrates the outer sheath of the coaxial cable and makes electrical contact with the shield structure.

The configuration of the blade terminal will be further described with reference to a three-sided view of the blade terminal 413 shown in FIG. As shown in FIG. 6, the blade terminal 413 includes a blade support 531 for contacting a part of the outer periphery of the outer cover 102 (see FIG. 5) of the coaxial cable 1 and a blade support 531.
And at least one blade 532 for penetrating the outer sheath 102 of the coaxial cable 1 and connecting to the shield structure 103.

The blade support 531 and the blade 53
2 are each formed of a conductor, for example, a metal.
The blade support 531 is provided on the outer cover 102 of the coaxial cable 1.
Has a curved shape so as to form a part of a cylinder following the outer circumference of, and contacts one of the blocks 410a or b. The blade supporting portion 531 is formed by cutting and raising a total of two blades 532 at two locations along the axial direction of the cylindrical surface which is configured to be curved and inward of the cylindrical surface. It is. Each of the blades 532 is divided into two parts, and a process for sharpening the tip is performed. As a result, the outer skin 102 can be easily pierced. Note that the blade support 531
The blade cut-and-raised portion becomes a through hole 535.

As described above, as shown in FIG. 5, the shield tap connector 410 includes a first block 410a and a first block 410a.
A second block 410b sandwiching the coaxial cable 1;
And the second blocks 410a, 410b are connected,
And a fastening bolt 412 for fastening the connecting member to be fixed. The fastening bolt 412 is formed of metal. The first block 410a and the second block 410b are provided with screw holes into which the fastening bolts 412 are inserted. The fastening bolt 412 is
Two bolts for fastening from the first block 410a side and two bolts for fastening from the second block 410b side may be provided. As the connecting member, any other member than the bolt may be used as long as the first block 410a and the second block 410b are fastened, connected and fixed. The connection terminal 411 is a terminal to which a connection wire is connected, and is electrically connected to the first block 410a, the second block 410b, or the tightening bolt 412. In the present embodiment, the tightening bolt 412 is inserted into the hole of the crimp terminal 140 (see FIG. 7C) connected to the end of the connection wire, and the crimp terminal 140 is moved by the head of the tightening bolt 412. Is pressed against the first block 410a.

The first block 410a has a concave portion 562 on the coaxial cable contact surface side. Also, the second
Similarly, a concave portion 568 is provided in the block 410b. These recesses 562 and 568 are tapered to follow the outer periphery of the coaxial cable 1 respectively. Also, the recess 562 of the first block 410a
Is provided with a recess for fixing the outer cover 102 of the coaxial cable 1 and the blade support 531. Further, the concave portion 562 of the first block 410a
One or more projections may be provided on the inner surface of the cable (not shown) so as to be arranged along a line parallel to the extension direction of the cable 1. The protrusion is provided at a position where the protrusion fits into a hole 535 formed by cutting and raising the blade 532 from the blade support portion 531 of the blade terminal 413. By fitting the protrusion into the hole 535, the blade terminal 413 is positioned with respect to the first block 410a. Alternatively, the outer side of the blade support 531 and the blade support 531
The protrusion may be provided at a position where the blade terminal 413 is sandwiched, for example, at a position just outside both ends of the blade terminal 413 in the longitudinal direction. In addition, the protrusions are provided in the first block 41.
The protrusion protrudes by a length equal to the thickness of the blade support portion 531 of the blade terminal 413 with reference to the curved surface of 0a. Thereby, the protrusion can be pressed against the outer cover 102 of the coaxial cable 1 together with the blade support 531.

When assembling the shield tap connector, the blade terminal 413 is fitted to the projection of the first block 410a, and the coaxial cable 1 is sandwiched and tightened between the first block 410a and the second block 410b. The portion is pressed against the surface of the outer cover 102 of the coaxial cable 1. In the process, the blade terminal 413
Blade 532 penetrates the outer cover 102 of the coaxial cable 1 and pierces the shield structure 103. Thus, the coaxial cable 1 and the blade terminal 413 are
First block 410a and second block 410b
Is fixed by

In this embodiment, the first block 410a
And the second block 410b and the screw are formed of metal. Thereby, the shield structure of the coaxial cable 1
A connection line is connected to the metal blade terminal 413, the first metal block 410a and the second block 410b, and a connection terminal electrically connected to the metal block terminal 413 and the second block 410b.

After the shield tap connector is assembled, an electric insulating tape or the like is wrapped around the surface to prevent unintended electrical contact with a surrounding metal object, for example, a support leg of the free access floor. desirable.

Next, regarding the high frequency grounding device 400,
This will be described with reference to FIGS.

As shown in FIG. 7A, the high-frequency grounding device 400 connects the conductive grounding plate 110, the surface of which is partially insulated, to the connection wire connected to the shield tap connector. For this purpose, a plurality of L-shaped tab terminals 100 which are protrusion terminals soldered to the ground plate 110 are provided. Further, as shown in FIG. 7C, a plurality of connection cables 1 connected to the plurality of L-shaped tab terminals 100, respectively.
60 is further provided. The connection wire is a conductive wire whose surface is coated with vinyl for insulation. A crimp terminal 140 which is a connection terminal for connection to the shield tap connector 410 is connected to one end, and the other end is connected. A plug-type connection terminal 150 such as a faston terminal connected to the L-shaped tab terminal 100 is connected to the portion.

As shown in FIG. 7B, the L-shaped tab terminal 100 includes a seat 102 electrically connected to the ground plate, and a connecting portion 104 to which the connecting line is connected.
Protrudes from the surface of the ground plate and is electrically connected to the seat. Also, the connecting portion 104 is laid so as to be parallel to the plane of the ground plate at the time of carrying in, and is raised so as to be substantially perpendicular to the plane of the ground plate when connecting the connection line. can do. This allows
At the time of carrying in, the grounding plate can be piled up, and carrying around becomes easy. Further, as shown in FIG. 7B, the L-shaped tab terminal 100 has a lock hole 106, and a lock projection is provided inside the plug-in connection terminal 150 (see FIG. 7B). Zu). When the L-shaped tab terminal 100 is inserted and fitted into the plug-in connection terminal 150, the plug-in connection terminal 150
The locking projection inside is configured to fit into the lock hole of the L-shaped tab terminal 100.

The protruding terminals are provided to facilitate connection to connection lines. In general, it takes time to connect the connection lines to the conductive plate, and a connection tool is required. In the embodiment of the present invention, the projecting terminal is soldered to the conductive plate in advance, as shown in FIG. Further, the tab terminals can be fitted without special tools. Instead of soldering, the tab terminals may be screwed to the ground plate, joined by welding, or crimped.

Instead of the L-shaped tab terminal 100, FIG.
T-shaped tab terminals 20 as shown in FIGS.
A plurality of 0s may be provided. 8A and 8B, the T-shaped tab terminal 200 includes a seat 202 electrically connected to the ground plate, and a coupling 204 to which a connection line is coupled. It protrudes on the surface of the ground plate and is electrically connected to the seat. The T-shaped tab terminal 200 is similar to the L-shaped tab terminal 100 in FIG.
As shown in FIG. 7B, a lock hole 206 is formed, and the T-shaped tab terminal 2 is inserted into the plug-in connection terminal 150 shown in FIG.
When 00 is inserted and fitted, the locking projection inside the plug-in type connection terminal 150 fits into the lock hole of the T-shaped tab terminal 200. In the case of the T-shaped tab terminal 200, the seat area is larger than that of the L-shaped tab terminal, so that the contact area with the ground plate increases.

Further, instead of the L-shaped tab terminal 100,
Notch terminal 1 as shown in FIGS.
A plurality of 80s may be provided. Notch terminal 18
In the case of No. 0, a part of the ground plate is cut in advance as shown in FIG. 9A, and the cut terminal 180 is raised and used at the time of construction as shown in FIG. 9B. Further, similarly to the L-shaped tab terminal 100, the notch terminal 180
As shown in FIG. 7B, a lock hole 306 is formed, and a notch terminal 1 is inserted into the plug-in connection terminal 150 shown in FIG.
When the plug 80 is inserted and fitted, the locking projection inside the plug-in connection terminal 150 fits into the lock hole of the cutout terminal 180. In this case, the thickness of the ground plate is set so as to fit into the plug-in connection terminal 150. When the cut terminal 180 is provided, there is no need to install a connection terminal such as a tab terminal. Also,
When carrying in, lay it down so that it is parallel to the plane of the ground plate, and when connecting the connection line, it can be raised almost perpendicular to the plane of the ground plate. At times, the grounding plates can be stacked to facilitate carrying. Also, for each of the cut terminals,
A connector for coupling the connection lines may be mounted.

Further, the material of the ground plate 110 can be a conductive metal such as copper, aluminum, and iron. Considering portability and handling, it is desirable that the thickness be as small as possible. Therefore, in this embodiment, a copper plate having a thickness of 0.2 mm is used. The planar size of the ground plate 110, of course, affects the capacitance. However, if the size is too large, it is inconvenient to handle or when a high-frequency noise disturbance occurs after the electronic device is installed, and a countermeasure is taken. Is too large, it is difficult to construct. Therefore, in the embodiment of the present invention, a 0.3 mx 0.3 m plate is used as a standard specification in consideration of ease of handling. In addition, the back surface of the ground plate 110 is insulated from the peripheral edge of the front surface. Commercial thickness 0.1 to ensure insulation
When coated with a so-called insulating film of about mm, good experimental results were obtained. Insulation processing is performed to prevent the grounding plate peripheral edge from coming into contact with the iron support legs of the free access floor plate to establish an electrical connection state, thereby preventing the capacitance effect of the grounding plate described later from being lost. It is. Further, the length of the connection line from the connection terminal 411 of the shield tap connector 410 to the ground plate is desirably 0.5 m or less. Further, the thickness of the connection line is desirably 1 mm ² or more in consideration of disconnection and the like.
Further, the number of connection lines is plural. Considering microscopically the situation in which the current spreads and flows from the connection point to the four sides on the ground plate, the high-frequency ground plate has a small capacitance connected to a point having a small inductance as shown in FIG. It can be considered as an equivalent model in which the components are repeatedly connected in series, and it takes time to propagate the current. Therefore, in the case of high frequency, the case of a relatively small ground plate with a size of 0.3 mx 0.3 m However, simply connecting to the central point of the plate does not effectively use the entire area of the plate. Therefore, as shown in FIG. 11, five connection terminals (connection lines 5
7) and three connection terminals (three connection lines) as shown in FIG. 7 so that the connection terminals are not close to each other on a diagonal line of a rectangular ground plate. Can be arranged. Considering the actual construction, it is quite troublesome to always connect the five connection lines. Therefore, in this embodiment, three connection lines are used. Further, the arrangement position of the L-shaped tab terminal 100 can be determined as described below. The high-frequency ground plate can be regarded as an aggregate of minute capacitors, as shown in FIG.
In this case, the inductance (L ₁ ) is established between the connection point of the connection line on the high-frequency ground plate (the position where the L-shaped tab terminal 100 shown in FIG. 7 is arranged) and each of the micro capacitors (C _{1 to} C _n ).
ＬL _n ). That is, considering microscopically the situation in which the current spreads and flows from the connection point to the four sides on the grounding plate, the high-frequency grounding plate has a small capacitance connected to a path having a small inductance as shown in FIG. This is considered as an equivalent model that is repeatedly connected in series. For this reason, as the distance from the connection point of the connection line on the high-frequency ground plate increases, the inductance increases, so that the effect of the capacitor is lost. This situation is schematically shown in FIGS. As shown in FIG. 12, when there is only one connection line, the entire high-frequency ground plate cannot be used effectively. On the other hand, when the number of connection lines is five and the connection positions of the connection lines are arranged as shown in FIG. 13, the high-frequency grounding plate can be used effectively. In this case, the L-shaped tab terminal 1
00, each circle having the same radius r assuming that the position where each of the 00s is arranged is the center of the circle,
Place them so that they do not overlap. When the circles are in contact with each other and the radius r has the maximum value, when the length of the high-frequency ground plate is a, it can be obtained by the equation as shown in Expression 1.

[0061]

R = (√2-1) a / 2 In the case where five L-shaped tab terminals 100 are arranged, in the case of a rectangular ground plate, one is arranged at a position where two diagonal lines intersect. Are arranged at four positions on a diagonal line separated by 2r from the arranged position. In this way, by arranging the positions where the L-shaped tab terminals 100 are arranged at a certain distance, the ground plate can be used more effectively.

In actual construction, the high-frequency grounding device having the above-described configuration is connected to the coaxial cable 1 and the MAU.
5 is laid on the floor of a building having a steel frame or a reinforced steel structure (in the case of a double floor free access floor, the floor of the house itself), as shown schematically in FIG. . In the embodiment of the present invention, as shown in FIG.
At a position adjacent to U5, a shield tap connector 410 is arranged so as to sandwich the coaxial cable 1 and
Is electrically connected to the shield structure. Furthermore, MA
The ferrite core 300 is mounted so as to sandwich the coaxial cable 1 close to both ends where the U5 and the shield tap connector 410 are mounted. At least one ferrite core 300 is mounted, and the mounting position of the ferrite core 300 is determined by tap blocks 5a and 5a of MAU5.
b, or at least one of both ends where the MAU 5 and the shield tap connector 410 are mounted. The above-mentioned ground plate is laid in close contact with the concrete floor surface of the building, and is fixed to the floor with an adhesive tape or the like. Each of them has a length of 0.5 m or less and a sectional area of 1 m.
One or more ends of each connection line are connected to the shield tap connector 410 by using a plurality of conductors of mm ² or more, and the other end of this connection line is separated from the plurality of protruding terminals of the ground plate and each other on the ground plate. Distributed connection at the specified position.

In the embodiment of the present invention,
With the aim of implementing with standard materials and construction methods, repeated experiments were carried out as described above as a method that would obtain the best results in terms of cost effectiveness. Therefore, although the size of the high-frequency grounding plate may be slightly larger or smaller, the above-mentioned dimensions are determined from the viewpoint of standardization, economy of material removal, and the like. In addition, according to the result of the impedance measurement, the material and the thickness of the ground plate hardly affect the effect.
On the other hand, it is important that the upper limit of the length of the connection line be suppressed to this level. However, the influence of the material and cross-sectional area of the connection wire is small. If the cross-sectional area is too small, the wire may be broken during handling, so a copper wire of 1 mm ² or more was used. In addition, in many cases, the peripheral edge of the ground plate touches the support leg of the free access floor plate and becomes electrically connected, so that the effect of the capacitance of the ground plate does not appear. Special attention must be paid to the insulation at the end face.

By connecting as described above, the shield tap connector 410, which is a noise reduction device, the ferrite core 300, and the high-frequency grounding device 400 are connected.

Next, the reason why noise is reduced by using the ferrite core, the shield tap connector 410, and the high-frequency grounding device in the present embodiment will be described.

In order to obtain a sufficient noise suppressing effect by using only the ferrite core 300, the MAU 5 needs a high-frequency current bypass path. By the way, inside the MAU, when the MAU receives transient electromagnetic interference, a circuit for bypassing the energy to the ground through the entire shield of the AUI cable (the cable connecting the MAU and the DTE) and the ground wire of the DTE. Is provided.
According to the JIS X 5252 standard, the impedance of the bypass circuit is 250 kΩ or more at 60 Hz,
It is specified to be 15Ω or less from 3 MHz to 30 MHz. In actual MAU, to satisfy this rule,
For example, a fixed resistor of 1 MΩ and a capacitor of 0.01 μF are connected in parallel between the shield portion of the coaxial cable and the metal fitting portion of the connector for connecting the AUI cable (the portion to which the entire shield of the AUI cable is connected). Circuit is formed. However, the length of the AUI cable is allowed up to 50 m, and the length of the ground wire of the DTE is undefined. The high-frequency impedance of 1 MHz or more of the bypass seen from the MAU causes parallel resonance, and the impedance is reduced. It is very unstable because there are many sharply rising frequencies. As described above, the ground wire of the DTE is long, and the ferrite core 300 which is an inductance element is used.
, The impedance when viewed from the MAU 5 is in a high impedance state, and a sufficient noise suppression effect cannot be expected.

On the other hand, FIG. 15 equivalently shows a connection state in the embodiment of the present invention when a high-frequency grounding device of a different system from the high-frequency current bypass provided in the MAU is provided. In FIG. 15, the ground plate can be regarded as an aggregate of minute capacitors. The inductance element of the ferrite core 300 and this ground plate cause a series resonance state at a high frequency of about 10 MHz.
, The ground impedance becomes a low impedance state. Therefore, the noise current flowing through the skin of the shield structure of the coaxial cable 1 is reduced by the ferrite core 30.
It is bypassed to ground via a zero inductance element and a ground plate that can be considered as a capacitor. Further, since the impedance of the shield structure of the coaxial cable viewed from the signal contact and the shield contact drawn from the coaxial cable 1 of the MAU5 is in a high impedance state due to the action of the inductance element of the ferrite core 300, the impedance is pulled out of the coaxial cable of the MAU5. The noise coupled to the signal contact and the shield contact can be reduced.

In the noise reduction device configured as described above, the measured value of the capacitive impedance between the ground as viewed from the terminal 411 of the shield tap connector 410 is 20 MHz.
It became 20Ω or less at z. In addition, JIS X 5252
The standard stipulates that one cable segment has one point ground. 60Hz of this high frequency grounding circuit
Is 1 MΩ or more, the single-point grounding of the coaxial cable is not broken by this high-frequency grounding circuit.

When the coaxial cable to which the MAU of the coaxial tap connector type is attached is exposed to a transient electromagnetic wave emitted by electrostatic discharge, the measured value of the noise voltage induced in the coaxial cable is as shown in FIG. Was. FIG. 17 shows a configuration diagram of the experiment. The procedure of the experiment will be described below.

(1) A floor panel A electrically insulated from the surroundings and a grounded floor panel B are arranged at a predetermined interval. Below these panels A and B, a grounded copper plate C is arranged on the floor. The panels A and B are supported on the copper plate C while being insulated by the support legs 901.

(2) The test coaxial cable 1 in which both ends of the cable are terminated by a terminator (not shown) having the same characteristic impedance, the center of the cable 1 coincides with the opposing surfaces of the floor panel A and the floor panel B. Place in position.

(3) Extremely high internal resistance (nominal 2 GΩ)
Connect the high-voltage power supply 910 to a conductive rubber cord (20 kΩ / m).
911 to connect to the insulated floor panel A.
Further, a disk electrode 922 is connected to the floor panel A via a conductive rubber cord 921, and an electrode 923 for detecting a potential of the surface voltmeter 920 is opposed to the disk electrode 921. In this state, the floor panel A is charged to a predetermined voltage (indicated by the surface voltmeter 920) by the high-voltage power supply 910,
Discharge occurs in a gap between the floor panel B and the grounded floor panel B. Actually, the interval between both panels is adjusted so that discharge occurs at the voltage to be tested.

(4) A digital oscilloscope (not shown) is connected to the terminator on one side of the test coaxial cable 1 and the noise voltage induced in the test coaxial cable 1 is measured.

(5) In the experiment, the test coaxial cable A to which no MAU is connected (corresponding to a link segment)
And a test coaxial cable B (corresponding to a cable segment) in which only one MAU is connected to the center of the cable,
Test coaxial cable C with only one MAU connected to the center of the cable and only the above-mentioned ferrite core attached
And only one MAU was connected to the center position of the cable and the test coaxial cable D equipped with the noise reduction device according to the embodiment of the present invention. The MAUs of the test coaxial cables B, C, and D include a branch cable (AUI cable) and a data terminal (DT).
E) is not connected. In FIG. 16, the peak-to-peak value of the noise voltage induced in the coaxial cable under test is
5 is a graph plotted for each discharge voltage between floor panels A and B. As shown in FIG. 16, the noise voltage induced in the coaxial cable B to which the MAU is connected increases about 1000 times as compared with the cable A to which the MAU is not connected. Moreover, the voltage is different from the rated amplitude (approximately 2 V) of the signal propagating on the cable when performing data communication.
It has reached several times the amplitude. In the test coaxial cable C equipped with only the ferrite core and the test coaxial cable D equipped with the noise reduction device according to the embodiment of the present invention, the measurement was performed only when the discharge voltage was 2 kV. As a result, compared to the noise voltage induced in the coaxial cable B, the coaxial cable C decreased to about 、 and the coaxial cable D decreased to about ４. As described above, according to the embodiment of the present invention using the ferrite core and the high-frequency grounding device, the noise voltage can be further reduced.

[0075]

According to the noise reduction apparatus of the present invention, it is possible to reduce noise due to electromagnetic interference such as transient electromagnetic waves radiated by electrostatic discharge in a transmission medium having a coaxial structure.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a noise reduction device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a system configuration example of a 10BASE5 format baseband coaxial system according to the JIS X 5252 standard.

[Fig. 3] (a) Coaxial taps shown in JIS X 5252 standard
FIG. 1 is a perspective view showing the concept of a connector, and FIG. 2 (b) is an explanatory view showing a typical coaxial tap connector circuit shown in JIS X 5252 standard.

FIG. 4 is an explanatory diagram showing a general connection method of a coaxial tap connector type MAU.

FIG. 5 is a configuration diagram of a shield tap connector according to the embodiment of the present invention.

FIG. 6 shows an example of a blade terminal used in the embodiment of the present invention, in which (a) is a plan view, (b) is a front view,
(C) Side view.

FIG. 7A is an external view of a high-frequency grounding device according to an embodiment of the present invention. (B) An external view of an L-shaped tab terminal according to the embodiment of the present invention. (C) An external view of a connection cable according to the embodiment of the present invention.

FIG. 8A is an external view of a high-frequency grounding device according to an embodiment of the present invention when a T-shaped tab terminal is used. (B) An external view of a T-shaped tab terminal in the embodiment of the present invention.

FIG. 9 (a) is an external view of a high-frequency grounding device according to an embodiment of the present invention, in which a notch terminal is used. (B) An external view of the high-frequency grounding device according to the embodiment of the present invention when a cut terminal is raised.

FIG. 10 is an explanatory diagram of an equivalent model of a high-frequency ground plate.

FIG. 11 is a diagram showing connection positions when connecting the ground plate with five connection lines in the embodiment of the present invention.

FIG. 12 is a schematic diagram showing the function of a minute capacitor when there is one connection line.

FIG. 13 is a schematic diagram showing the function of a micro capacitor when there are five connection lines.

FIG. 14 is a diagram schematically illustrating a grounding method according to the embodiment of the present invention.

FIG. 15 is an explanatory diagram equivalently showing a connection state in the embodiment of the present invention.

FIG. 16 shows the peak-to-peak value of the noise voltage induced in each of the test coaxial cables A, B, and C by using the floor
7 is a graph plotted for each discharge voltage between panels.

FIG. 17 is an explanatory diagram showing a configuration of an experiment for examining a noise voltage induced at an end of a coaxial cable by being exposed to a transient electromagnetic wave.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Coaxial cable, 2 ... Branch cable (AUI cable), 3 ... Data terminal device, 5 ... Medium connection unit (M
AU) 5a and 5b: tap block, 50: connector housing, 300: ferrite core, 410: shield tap connector, 411: connection terminal, 400: high-frequency grounding device, 401: terminal, 402: connection wire, 102
... outer skin, 103 ... shield structure, 104 ... insulating layer, 1
05 ... Center conductor, 410a and b ... Block, 412
... fastening bolts, 413 ... blade terminals, 562 and 568 ... recesses, 531 ... blade support portions, 532 ...
Blade, 535: through hole, 100: L-shaped tab terminal, 1
10 ground plate, 120 insulating film, 102 and 2
02: Seat, 104 and 204: Joint, 106 and 206: Lock hole, 130: Vinyl insulated wire, 14
0: crimp terminal, 150: plug-in connection terminal, 200:
T-shaped tab terminal, 910 ... high voltage power supply, 921 and 9
11 ... conductive rubber cord, 922 ... disk electrode, 923 ... electrode, 920 ... surface electrometer, 901 ... support leg.

Continuation of the front page (56) References JP-A-6-231813 (JP, A) JP-A-6-104066 (JP, A) JP-A-56-159072 (JP, A) JP-A-59-98481 (JP) JP-A-56-15902 (JP, A) JP-A-1-126774 (JP, A) JP-A-59-86669 (JP, U) JP-A-62-118356 (JP, U) 6-50392 (JP, U) Hira 3-22359 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01R 4/64-4/66 H01R 4/24 H01R 13 / 648-13/719 H01R 9/05 H02G 15/00

Claims (2)

(57) [Claims] 1. A noise reduction device for a transmission medium in which a transmission medium having a coaxial structure having a center conductor, an insulating layer, a shield structure, and an outer skin is branched and used. A shield tap connector electrically connected to a shield structure of the transmission medium; an inductance element adjacent to a branch portion of the transmission medium, into which the transmission medium is inserted and connected; a conductive ground plate; The shield tap connector has a plurality of connection lines for electrically connecting the conductive ground plate and the shield tap connector, and the shield tap connector is connected to the plurality of connection lines and electrically connected to the shield structure of the transmission medium. Connection terminals which are connected to each other, and the plurality of connection lines are respectively provided at different positions of the ground plate.
A noise reduction device for a transmission medium, which is connected and connected . 2. A noise reduction device for a transmission medium according to claim 1.
Wherein the shield tap connector includes the transmission
Between the branch portion of the medium and the inductance element.
A noise reduction device for a transmission medium, which is provided.