JPH0670909B2 - High frequency grounding method for electronic devices - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention makes it easy and economical not only to newly install an electronic device, but also to make a supplementary construction in the event of a malfunction.
Effective in suppressing high frequency noise up to about 20 MHz,
The present invention relates to a high frequency grounding method for electronic devices.

[0002]

2. Description of the Related Art Electronic equipment is always grounded through a ground terminal of a distribution board, which serves as its power source, as shown in FIG. However, the so-called ground wire in this case has a relatively small electric resistance because it is a sufficiently thick wire, but since it is long, it has a low impedance against commercial AC and DC, but it is often used in electronic devices. For suppression of high frequency noise, which is a problem,
The inductance and hence the impedance are high and useless. In the case shown, the cross-sectional area of the ground wire is sufficiently large,
Although the resistance value is almost 0 Ω, the inductance changes depending on the thickness and the cross-sectional shape (for example, flat braided wire), but when it is considered to be 0.5 to 1 μH per 1 m, the frequency is 10
In the case of MHz, even if the inductance is 0.5 μH / m, the impedance becomes 1570 Ω at 50 m, which means that it does not function as a ground conductor from a high frequency standpoint.

Therefore, in electronic equipment, so-called high-frequency grounding is also commonly used, as shown in FIG.
In the conventional example, a copper plate having an area of 0.3 m ² or more and a thickness of about 0.8 mm regardless of the shape is conductively bonded to the concrete floor surface on the steel frame of the building to be used as a grounding plate, and a length of 1 They were connected by one connecting wire having a cross-sectional area of 3.5 mm ² or more within 0.5 m.

[0004] In the past, when paying particular attention to high-frequency noise at the time of new installation, as shown in Fig. 4, a large-area copper plate is laid on the entire free access floor under the electronic equipment, and when a plurality of copper plates are provided. There is an example in which each copper plate is connected by a braided wire, the copper plate and the device housing are connected at multiple points by a braided wire, and a rubber plate is laid between the copper plate and the floor for insulation. This method yielded good results, but it was difficult to construct except at the time of new construction, and required a great deal of cost.

[0005]

The present invention does not have the problems of the above-mentioned conventional high-frequency grounding method, is effective up to a frequency of about 20 MHz or higher, and can use standard materials and construction methods. An object of the present invention is to provide a high-frequency grounding method for an electronic device, which is economical, and which can be easily installed not only when a new electronic device is installed but also as a countermeasure when a defect occurs, as a complementary measure.

[0006]

In order to solve the above-mentioned problems, in the present invention, the electronic equipment and the high-frequency ground portion of its housing are placed on the conductive structure of the building with a floor material therebetween. Connect to the conductive ground plates, which are installed separately for each part, and whose surface is insulated, including the peripheral end faces, by using multiple connecting wires to disperse the ground plates at positions distant from each other. More specifically, more specifically, the area of the ground plate is reduced and the length of each connection line is shortened so that the capacitive impedance between the ground plate including the connection line and the conductive structure of the building is 20 MHz. It was decided to suppress to 20Ω or less.

[0007]

As shown in FIG. 3, the ground plate used for high-frequency grounding has an electrostatic capacity between it and the steel frame which is the conductive structure of the building. The steel frame is a raised land, and can be considered to be equivalent to the ground.

The inventor of the present invention is a measuring device based on the same principle as a potentiometer in which no current flows from the measuring terminal to the measuring device itself. Fig. 5 (in the figure, the solid line shows the value when the high-frequency ground plate is attached to the ground wire, and the dashed line shows the value when the high-frequency ground plate is used alone). The results for the grounding wire alone are shown by the broken line). The grounding wire used here had a cross-sectional area of 14 mm ² , an estimated length of 50 m or more, and the high-frequency grounding plate was a rectangular copper plate of 0.3 m × 1 m, which had a thickness of 0.
2 mm, one connecting wire, length 0.5 m, cross section 3.5
It was mm ² .

In the case of the grounding wire alone, the impedance increases in proportion to the frequency, shows a maximum at around 4 MHz, and then rises and falls in a complicated manner. This is because only the inductance is effective up to the first maximum point and the impedance is increased in proportion to the frequency, but from that point onwards, the stray capacitance to the ground (steel frame) of the ground wire is also effective,
In other words, it seems that it has to be handled as a distributed constant circuit. Further, in the case of a single high-frequency grounding plate, the impedance initially shows a capacitance characteristic that decreases with frequency, but it starts to increase after passing the minimum point in the vicinity of 10 MHz. This seems to be due to the influence of the inductance of the short connecting wire that is absolutely necessary for measurement.

Further, the state where the high frequency ground plate is attached to the ground line is similar to the high frequency ground state of an actual electronic device, but in this case, the capacitance of the high frequency ground plate and the inductance of the ground line are in parallel. In a circuit that is close to parallel resonance in the circuit, it shows a maximum value around a little over 1 MHz, and then it is close to series resonance in a circuit in which the inductance of the ground wire and the capacitance of the high frequency ground plate are in series. It becomes a minimum in the vicinity of 10 MHz, then increases and decreases to several tens of MHz, and then increases and decreases considerably in the upper frequency range. This is because all frequencies at this side must be treated as distributed constant circuits as described above.

The example shown in FIG. 4 in which a good effect is obtained in the prevention of high frequency noise by the conventional technique is shown schematically in FIG.
As shown in (a). As described above, the method of the conventional example shown in FIG. 4 can be installed when a new device is installed, but it is difficult to install after that and the installation cost is high. As shown in FIG. 6A, the large high-frequency ground plate used here is shown in FIG.
Since it was considered that the same effect could be obtained by dividing as schematically shown in (b), it was confirmed through experiments that a rather good result was obtained in terms of frequency. Also, if the device or housing to be grounded is not too large, it is not necessarily multi-point grounding, and the device or housing is connected at one site while using a plurality of connecting lines as shown in FIG. 6 (b). It was thought that almost the same effect could be obtained even if they were dispersedly connected on the ground plate divided into two, respectively, at positions distant from each other, so experiments confirmed that the results were as expected.

[0012] In carrying out the present invention, the electronic equipment and its housing are placed on the conductive structure of the building with a floor material between each of the high-frequency grounding parts and the surface including the peripheral edge surface. A conductive ground plate of 0.3 m on each side that has been subjected to insulation processing on each side and has a cross-sectional area of 1
A method in which three or more conductors of mm ² or more are used to disperse and connect each of the wires at positions separated from each other on a ground plate is adopted as a standard high-frequency grounding method for electronic devices, and can be implemented very easily.

In the present invention, high-frequency grounding is carried out with the aim of implementing standard materials and construction methods, and repeated experiments are carried out, and the method described above is used as the method of obtaining the best result in terms of cost efficiency. Of. Therefore, the size of the high-frequency grounding plate may of course be slightly larger or smaller, but the dimensions have been determined in view of standardization and economical efficiency of material taking. In addition, in the result of the impedance measurement, the material and the thickness of the ground plate hardly influence the effect. On the other hand, a connecting wire (a thick conductor for directly connecting the ground electrode of the distribution board to the ground is called a ground wire in the description of FIG. It is important to limit the upper limit of the length of the line connecting to the ground plane to the connecting line). However, the influence of the material and cross-sectional area of the connecting wire is small. If the cross-sectional area is too thin, it may break during handling, so we decided to use copper wire of 1 mm ² or more.
In many cases, the peripheral edge surface of the ground plate touches the supporting legs of the free access floor plate and becomes electrically connected, so that the effect of the capacitance of the ground plate does not appear. It turns out that special care must be taken regarding the insulation of this end face.

[0014]

[Examples] The problem of high frequency noise is that, as a result of the large amount of various electronic devices being used in recent years, noise generated by nearby devices may cause trouble, or may itself be a source of noise. As a result, a situation in which the operation of other electronic devices is disturbed is likely to occur. Of course, the standard is set in advance so that unnecessary electromagnetic fields above a predetermined value are not generated, but noise (generally referred to as the above-mentioned useless electromagnetic fields is referred to as the above-mentioned useless electromagnetic field) due to extremely slight changes in the operating state or aging of members. , Noise is not actually sound, but generally refers to something that causes an electronic device to malfunction). Generally, this kind of failure rarely always occurs reliably,
This is a so-called intermittent disorder, but it is difficult to deal with it and it is impossible to leave it alone. In other words, although it often occurs as an obstacle to be dealt with, it is quite difficult to confirm the effect of the countermeasure. For this reason, the present inventor standardized the materials for high-frequency grounding and the construction method, and made a standard countermeasure kit so that anyone anywhere could easily take countermeasures.

The high-frequency grounding plate actually used in the past is a rectangular copper plate having a size of 1000 mm × 300 mm and a thickness of 0.8.
It was about mm. However, the present inventor has
The so-called impedance analyzer, which has a well-established reputation in the range of 00 MHz, is used to measure the potential difference between both measurement terminals due to the current flowing through the impedance measurement target. As a result of repeating the impedance measurement experiment using (no current flows), even if the material of the plate is replaced with copper, aluminum, iron, and the thickness is changed to 0.2 mm, 0.5 mm, 2.0 mm, It turned out that no difference was observed. Iron is the cheapest, but we chose a copper plate with a thickness of 0.2 mm considering the convenience of handling.

The planar size of the grounding plate, of course, affects the electrostatic capacity, but the conventional size is too large and inconvenient to handle, and high frequency noise may occur after the electronic equipment is installed. It has been experienced that it is difficult to construct because it is too large even when taking measures for the above, so 0.3 m × 0.3
When the relationship between the impedance and the frequency was examined for a ground plate of m, 0.3 m × 0.6 m, and 0.3 m × 1 m, the value in the case of 0.3 m × 0.3 m in FIG. The solid line shows the value in the case of 0.6 m × 0.3 m and the broken line shows 1.0 m.
The result as shown in (dotted line) is shown in the case of × 0.3 m). The minimum impedance value is slightly smaller as the plate area is larger, but the frequency at which the minimum impedance value appears is smaller as the area is larger, and it is the smallest at the 20MHz side for a small 0.3m × 0.3m plate. The value is appearing. This is considered to be due to the influence of the inductance of the connecting line. In addition, a distributed-constant circuit-like state appears from the area where the minimum impedance value appears. In the present invention, in consideration of easiness of handling, 0.3 m × 0.3
We decided to use the m plate as the standard specification. If the ground plate is electrically connected to the steel frame of the building or the iron support legs of the free access floor plate as described above, the capacitance effect of the ground plate will be lost, so The surface, including the end faces, must be insulated. The present inventor has obtained good results by covering with a commercially available so-called insulating film having a thickness of about 0.1 mm for reliable insulation. As mentioned above, it was unexpectedly often the case that the peripheral edge surface of the grounding plate comes into contact with the iron support legs of the free-access floor plate, resulting in an electrical connection, so we paid particular attention to the insulation of the end surface.

As described above, the size of the ground plate is 0.3.
When m × 0.3 m, how to connect between the side of the electronic device or its housing and the ground plate becomes a problem. The impedance was measured when the ground plate was formed into the shape and size described above and connected by a single connecting wire having a length of 0.5 m, 1.0 m, 1.5 m, and 2.0 m. In the figure, the value when 0.5 m is a solid line, 1.0
The results in the case of m are shown by the broken line, the values of 1.5 m are shown by the one-dot chain line, and the values of 2.0 m are shown by the two-dot chain line). Also in this example, it is understood that the length of the connecting line must be 0.5 m or less in order to obtain a low impedance up to around 20 MHz.

Furthermore, even if a ground plate having a size of 0.3 m × 0.3 m is connected by a plurality of lines having a length of 0.5 m or less, there arises a problem of how many wires should be connected. Considering microscopically the situation in which a current spreads and flows in all directions from the connection position on the ground plate, consider a model in which microcapacitors are connected in series at the end of a path with a microinductance. Since it takes time for the current to propagate, in the case of high frequency, the size is 0.3 m ×
Even in the case of a comparatively small ground plate of 0.3 m, the total area of the plate is not effectively utilized only by connecting it to one point in the center of the plate. Therefore, the impedance was measured for the case where 1 to 5 connecting wires were used as shown in FIG. The result is shown in FIG. 2 (b) (values in the case of 5 lines are shown by solid lines, values in the case of 3 lines are shown by broken lines, values in the case of 1 line are shown by dashed lines). Considering the actual construction, it is very difficult to connect the 5 connecting wires, so I decided to connect with 3 wires. 30 if 3
The impedance is lowest at around MHz, which is considered to be sufficient. In order to simplify the work, tab terminals were attached to the high-frequency grounding plate at planned connection positions, and faston terminals matching the tab terminals were attached to the connection wires.

When the countermeasure work was carried out using the standard kit, the effect was recognized in the case of about 80%. High-frequency noise is an intermittent disturbance, and it is difficult to actually deal with it. It is considered that the achievement of 80% is almost satisfactory.

[0020]

As described above, according to the present invention, a relatively small and easy-to-handle, for example, 0.3 m square,
While using the grounding copper plate, the length of the wire connecting the grounding plate and the electronic device or the housing is short, for example, 0.5 m or less,
Since the number of connecting lines is reduced and the number of connecting lines is reduced to three, for example, the number of connecting points to the ground plate is distributed to a plurality of points, 20 MH
A sufficiently low grounding impedance can be obtained up to a high frequency of about z. Moreover, by standardizing the materials and construction methods as described above, the cost can be kept low and it is possible to easily take measures against high frequency noise. It was

[Brief description of drawings]

FIG. 1 (a) is a diagram showing the relationship between ground impedance and frequency when the size of a high-frequency ground plate is changed, FIG.
(B) is a figure which shows the relationship between the grounding impedance and frequency when changing the length of the connection wire (however, one piece) of a high frequency grounding board.

FIG. 2 (a) is a diagram showing a connection position when the standard ground plate of the present invention is connected by five connection lines, and FIG. 2 (b) is a connection line of the standard ground plate having a length of 0.5 m. It is a figure which shows the relationship between the grounding impedance and the frequency at the time of connecting with 1, 3, and 5, respectively.

FIG. 3 is a diagram showing a state in which an electronic device is grounded by a grounding wire and a high-frequency grounding plate at a distribution board that has been conventionally generally used.

FIG. 4 is a diagram illustrating a method in which a good high-frequency noise countermeasure effect is obtained among the conventional grounding methods.

FIG. 5 is a diagram showing the relationship between the ground impedance and the frequency measured when grounded by the conventional grounding method.

6 (a) is a diagram for schematically explaining the conventional grounding method shown in FIG. 4, and FIG. 6 (b) is a diagram for schematically explaining the grounding method of the present invention by standard materials and standard construction. Is.

Claims (2)

[Claims] 1. An electronic device and a high-frequency grounding part of its housing,
Separately installed on the conductive structure of the building by separating the floor material, using a plurality of connecting wires to the conductive ground plate with the surface insulation including the peripheral end face installed separately for each of the above parts. A high-frequency grounding method for electronic equipment, characterized in that the grounding plates are dispersed and connected at positions separated from each other. 2. The area of the ground plate is made small and the length of each connecting line is made short so that the capacitive impedance between the ground plate including the connecting line and the conductive structure of the building is 20 MHz at 20 MHz.
The high frequency grounding method for an electronic device according to claim 1, wherein the high frequency grounding is suppressed to Ω or less.