TWM479496U - Cable shield structure of preventing common mode interference - Google Patents

Description

Cable shielding structure for preventing common mode signal interference

The present invention relates to a cable shielding structure for preventing common mode signal interference, in particular to a mela having electrical insulation effect between the inner shielding layer and the outer shielding layer, and the inner shielding layer and the outer shielding layer. A cable shielding structure that prevents electrical common mode interference from being electrically connected to each other without being electrically connected to each other.

As shown in the third figure, the differential-mode Single is also called normal mode, series mode, line-to-line sensing, and symmetrical signal. In the two-wire cable transmission loop, each line-to-ground voltage is represented by the symbol V. ₁ and V ₂ are indicated. The differential mode signal component is V _DIFF . The pure differential mode signal is V ₁ =-V ₂ , which are equal in magnitude, 180° out of phase, V _DIFF =V ₁ -V ₂ , because V ₁ and V ₂ are symmetrical to ground, so no current flows through the ground. The circuit of the differential mode signal is shown in the third figure. All differential mode currents (I _DIFF ) flow through the load. Differential mode interference invades the two signal lines, and the direction is consistent with the signal current square. One is generated by the signal source, and the other is generated by electromagnetic induction during transmission. It is in phase with the signal and is in phase. Hard to suppress.

Common-Mode Single is also called ground-sensing signal or asymmetric signal. The common-mode signal component is V _com , and the pure common-mode signal is: V _com =V ₁ =V ₂ , the size is equal, and the phase difference is 0°. V ₃ =0. The circuit of the common mode signal is as shown in the fourth figure. When the interference signal invades between the line and the ground, the interference current flows through one-half of each of the two lines, and the ground is a common circuit. In principle, the interference is relatively easy to eliminate. In the actual circuit, the common-mode interference (Common-mode Interference) is converted into crosstalk interference that is difficult to eliminate due to the unbalanced line impedance.

There are two kinds of changes in voltage and current through the wire. We call this the power line of "common mode" and "differential mode" equipment, the communication line of telephone, etc., and the communication line exchanged with other equipment or peripheral equipment. There are at least two wires that carry power or signals as a round trip line. But there is usually a third conductor outside the two wires, which is the "ground". There are two types of interference voltage and current: one is that two wires are respectively transmitted as round-trip lines; the other is that two wires are used as paths, and the ground wires are used for return path transmission. The former is called "Differential-Mode" and the latter is called "Common-Mode".

Interference types are usually classified into common mode interference (Common-Mode Interference) and differential mode interference (Differential-Mode Interference) according to different interference modes. Common mode interference and differential mode interference are a common classification method. Common touch interference is the potential difference between the signal and the ground, which is mainly formed by the grid-in, ground potential difference and the common-state (same-direction) voltage induced by the space electromagnetic radiation on the signal line. The common-mode voltage is sometimes large, especially In the power supply room of the distributor with poor isolation performance, the common mode voltage delivered by the transmitter is generally higher. The common mode voltage can be converted into a differential mode voltage through an asymmetric circuit, which directly affects the measurement and control signals, causing component damage (this is the main reason for the high damage rate of some system I/O modules). This common mode interference can be DC. It can also be an exchange. Differential mode interference refers to the interference voltage acting between the two poles of the signal, mainly caused by the coupling of the space electromagnetic field between the signals and the conversion of the common mode interference by the unbalanced circuit. Pressure, this allows direct superimposition on the signal, directly affecting measurement and control accuracy.

A mask is a metal separation between two spatial regions to control the induction and radiation of electric, magnetic and electromagnetic waves from one region to another. Specifically, the mask body is used to surround the component, circuit, assembly, cable or the interference source of the whole system to prevent the interference electromagnetic field from spreading outward; the cover circuit is used to surround the receiving circuit, device or system to prevent them. Under the influence of external electromagnetic fields. Because the mask body absorbs energy (eddy current loss), reflected energy (electromagnetic wave reflection on the mask) and cancels energy for external electromagnetic waves and internal electromagnetic waves from wires, cables, components, circuits or systems. The electromagnetic induction generates a reverse electromagnetic field on the mask layer, which can cancel the effect of partially interfering with the electromagnetic wave. Therefore, the mask body has the function of reducing interference.

(1) When the frequency of the interfering electromagnetic field is high, the eddy current generated in the metal material of low resistivity is used to form a canceling effect of the external electromagnetic wave, thereby achieving the effect of the mask.

(2) When the frequency of the interfering electromagnetic wave is low, a material with a high magnetic permeability is used, so that the magnetic field line is confined inside the mask body to prevent diffusion into the space of the mask.

(3) In some cases, if high-frequency and low-frequency electromagnetic fields are required to have a good masking effect, different metal materials are often used to form a multilayer mask.

The so-called "mask" on the cable structure is essentially a measure to improve the electric field distribution. The cable conductor is formed by stranding a plurality of wires, and an air gap is easily formed between the cable conductor and the insulating layer, and the surface of the conductor is not smooth, which causes electric field concentration. A layer of semiconducting material is applied on the surface of the conductor, which is equipotential with the masked conductor and in good contact with the insulating layer, thereby avoiding partial discharge between the conductor and the insulating layer. This mask is an inner mask. The layer may also have a gap at the contact between the insulating surface and the sheath, which is a factor causing partial discharge, so a layer of semi-conductive is added to the surface of the insulating layer. a mask layer of an electrical material which has good contact with the masked insulating layer and equipotential with the metal sheath to avoid partial discharge between the insulating layer and the sheath, the mask being an outer mask layer; In the case of a sheathed insulated cable without a metal sheath, in addition to the semi-conductive mask layer, a metal mask layer wrapped with a copper strip or a copper wire is added. The metal mask has two main functions, one is when the cable is energized. The generated electromagnetic field is shielded in the insulated core to reduce electromagnetic interference to the outside world. Secondly, the fault current in the design range generated by the system is safely introduced into the grounding system to protect the system from safe operation. This metal mask layer passes the capacitive current during normal operation; when the system is short-circuited, it acts as a short-circuit current channel and also acts as a masking electric field. It can be seen that if the outer semi-conductor layer and the copper mask are not present in the cable, the possibility of insulation breakdown between the core and the core in the three-core cable is very large. The main purpose of stripping a small section of the mask layer when making the cable termination or joint is to ensure the creepage distance of the high voltage to the ground. The stress at the fracture of the mask is very concentrated, which is a weak link! Appropriate measures must be taken for stress treatment (using stress cones or stress tubes, etc.) to remove the length of the mask layer to ensure creepage distance; and to enhance the creep resistance of the insulation surface. Excessive stripping of the mask layer will increase the difficulty of construction, and the cost of adding cable accessories is completely unnecessary.

In view of this, the creators of this case are investigating and innovating to reveal the new cable shielding structure that prevents common mode signal interference.

The purpose of the present invention is to provide a cable shielding structure for preventing common mode signal interference, comprising: at least two power lines for transmitting power; at least one signal line, each of which has an outer layer surrounding the insulating layer for transmission Signal; the inner ground line is adjacent to the signal line; the inner insulation layer is wrapped around the same group of signal lines, or the signal line and the inner line of the inner line; The shielding layer is wrapped around all power lines, signal lines, and inner ground lines for shielding; the outer shielding layer is wrapped around the outer periphery of the inner shielding layer; and the outer protective layer is wrapped around the outer shielding layer The outer periphery of the present invention is characterized in that: between the inner shielding layer and the outer shielding layer, a mela having electrical insulating performance is interposed, so that the inner shielding layer and the outer shielding layer are electrically insulated from each other. Do not conduct each other.

The cable shielding structure disclosed in the present invention for preventing common mode signal interference, wherein the inner ground line is selected from the group consisting of copper clad steel, copper clad copper, and tin copper alloy.

(10) ‧‧‧ Cable shielding structure to prevent common mode signal interference

(11)‧‧‧Power cord

(12) (12') ‧ ‧ signal line

(13) ‧‧‧Mainline

(14) ‧‧‧Insulation

(15) ‧ ‧ inner shield

(16) ‧‧‧ outer shield

(17) ‧‧‧ Exterior protective layer

(18)‧‧‧Mella

The first picture is a schematic cross-sectional view of the cable shielding structure of the novel to prevent common mode signal interference.

Second figure: is a schematic cross-sectional view of a conventional cable shielding structure.

The third picture is a schematic diagram of the conventional differential mode signal.

Figure 4: Schematic diagram of the conventional common mode signal.

Referring to the first figure, the present invention relates to a cable shielding structure (10) for preventing common mode signal interference, comprising: at least two power lines (11); at least one signal line (12) (12'), the inland The wire (13), the inner insulating layer (14), the inner shield layer (15), the outer shield layer (16), and the outer protective layer (17) have the same structure.

Referring to the first figure, the present invention discloses a cable shielding structure (10) for preventing common mode signal interference, wherein two power lines (11) (red lines and black lines) are transmission power sources. As for the outer edge of each signal line (12) (12'), the insulating layer is wrapped to transmit signals (for example: 2P in USB2.0) The signal line (12') is white line and green line; as for the 2P signal line (12) (purple line, orange line, yellow line, blue line) in USB3.0. The above-mentioned inland line (13) is adjacent to the 2P signal line (12) in USB 3.0. As for the inner insulating layer (14), they are wrapped around the same group of signal lines (12) (ie 2P signal lines (12) (purple, orange, yellow, blue) in USB3.0) and the inner line. (13) the periphery; or only around the same group of signal lines (12') [ie, the 2P signal line (12') (white line and green line) in USB2.0. The inner shield (15) is wrapped around the entire power line (11), signal line (12) (12'), and inner ground (13) for masking. The outer shield layer (16) is wrapped around the outer shield layer (15). The outer protective layer (17) is wrapped around the periphery of all the shielding layers (16).

The present invention is characterized in that between the inner shielding layer (15) and the outer shielding layer (16), a Mylar (18) having electrical insulation performance is interposed to shield the inner shielding layer (15) from the outer shield. The layers (16) are electrically insulated from each other and are not electrically connected to each other.

In addition, when wiring, the cable shielding structure (10) of the present invention for preventing common mode signal interference should be kept away from the high voltage line, and the high voltage power line and the signal line (12) (12') should not be bundled together.

The structure and shape disclosed in the present invention can be modified and applied under the spirit or scope of the present invention, and the present invention is not limited.

(10) ‧‧‧ Cable shielding structure to prevent common mode signal interference

(11)‧‧‧Power cord

(12) (12') ‧ ‧ signal line

(13) ‧‧‧Mainline

(14) ‧‧‧Insulation

(15) ‧ ‧ inner shield

(16) ‧‧‧ outer shield

(17) ‧‧‧ Exterior protective layer

(18)‧‧‧Mella

Claims (1)

A cable shielding structure for preventing common mode signal interference includes: at least two power lines for transmitting power; at least one signal line, each of which has an outer layer surrounding the insulating layer for transmitting signals; the inner ground line is adjacent It is located beside the signal line; the inner insulation layer is wrapped around the same group of signal lines, or the same group of signal lines and the inner line of the inner line; the inner shielding layer is wrapped around all the power lines, signal lines, and the inner ground line. a periphery for shielding; an outer shielding layer wrapped around the outer periphery of the inner shielding layer for shielding; and an outer protective layer wrapped around the outer periphery of the outer shielding layer; characterized in that: the inner shielding layer and the outer shielding layer Between the layers, a Mylar having electrical insulation performance is interposed, so that the inner shield layer and the outer shield layer are electrically insulated from each other and do not conduct each other.