High-frequency balanced shielded cable

FIELD: electrical engineering; balanced high-frequency cables for data transfer.

SUBSTANCE: proposed cable has core formed by polyethylene or porous polyethylene insulated conductors twisted together to form pair and filler disposed between insulated conductors and cable shield covered with sheath on top. Used as filler are untwisted fibrillated polypropylene threads longitudinally disposed throughout entire cable length. In wiring this cable needs bending through very small radius (below ten-fold of cable outer diameter.

EFFECT: reduced capacitance and attenuation factor, enhanced stability of cable throughout entire operating frequency range.

1 cl, 4 dwg

The invention relates to one of the branches of the electrical industry - cable technique, more specifically, to the balanced high-frequency shielded cables for data transmission. The following cables are used to organize the transmission of digital signals in the systems of industrial automation process control. Due to the specifics of the installation and operation of cables in industrial production design must have high flexibility (low bending radius) and high stability of electrical parameters for high-speed transmission of digital streams.

Known symmetric high-frequency shielded cables containing a core formed insulated electric conductors, twisted together in a pair, and a filler of polymer material, on top of which is the screen and the shell.

The filler is extruded in the form of a continuous polymer layer over the pair, which allows to obtain a symmetrical design, and this, in turn, ensures the stability of the parameters of the transmission cable. However, this design has a high rigidity and material, as well as stable, but relatively low electrical parameters, in particular the relatively high capacitance, which, in turn, leads to deterioration of other parameters the ditch, depend on it. [1]

Known symmetric high-frequency shielded cables containing a core formed insulated polyethylene or porous polyethylene electric conductors, twisted together in a pair, and a filler made of polymer filaments, on top of which are the screen and the shell. The polymeric filaments United into bundles and twisted insulated conductors. They, being flexible elements do not reduce the flexibility of the cable, but twisting the harness with the wires of the pair (the so-called star twisting) breaks the symmetry of its design. This is a consequence of the fact that when the twist along the length of the cable is alternating locations withing the part between the shield and the insulated conductors and the other part between the two insulated conductors. These cables are the closest (essential features) analogue of the invention under examination.

The invention relates to symmetrical high frequency cable containing insulated conductive wires, twisted together in a pair, the screen and the shell. Between these conductors and the shield (in mergelina space) is a filler made of insulating material. The specified placeholder in varying degrees, affects all the main characteristics of these cables. If this is m this effect depends on the material of the filler, and from his "design" (patterns), and location relative to the cable elements between which it is placed.

This invention considers these issues, and the technical result, which will be shown below, resulting from the use of a filler made of a certain material with a certain structure and a certain way located relative to the structural elements of the cable.

The main electrical parameters of the symmetric cable is capacity, attenuation coefficient and wave resistance. The capacitance of the cable (wires and a screen which are capacitor plates, and insulating material, its dielectric) depends in particular on the kind of material forming the dielectric, i.e. its dielectric constant ε_r. In the case under consideration is the dielectric constant meerilinga space that hosts a placeholder.

The attenuation coefficient characterizes the reduction of electromagnetic energy when you spread it on cable. The reduction or attenuation of energy due to her loss in the transmission line. Part of the energy consumed by the dielectric losses in mergelina space, but the cables that require increased design flexibility while maintaining normalized level of losses that occur in the t the problem of ensuring the symmetry of the structure. In this case, the mean difference of the conditions of the location of each pair of veins in relation to the screen, which is characterized by a capacitive asymmetry lived. The signal transmission cable with a capacitive asymmetry lived has the following feature: due to the differential velocity of propagation (electromagnetic waves) for each couple lived on the target load (receiving device) can be observed frequency peaks losses. This phenomenon manifests itself at certain frequencies for a given cable length, when the electromagnetic waves coming in each pair of veins, in the receiving device are formed in antiphase. The magnitude of the wave resistance is normalized. For this cable is 100 to 150 Ohms.

So, the problem is clear, and the task that needed to be addressed when implementing the invention, is as follows: create a cable that allows multiple bends with small radius, while ensuring (or decrease) the low level of losses in the whole range of operating frequencies. The technical result, which is obtained from testing of an experimental batch of cables is the small radius of the mounting bends (less than ten times the outer diameter of the cable), the decrease in capacitance of the cable, reducing the coefficient of attenuation and ensuring stability throughout the operating frequency range.

For capacity reduction was necessary item in order to get the placeholder, which would reduce the specified dielectric constant meerilinga space.

As the material of the filler were chosen the same as in the prototype, the polymer strands. However, if the prototype filaments United into bundles, in this case, structurally, the filler is made differently. The only similarity placeholder flexibility. In the prototype, the material of the filaments is given on the functional level (polymer)does not contain the thread structure.

In the invention used threads, developed by OOO "NPP" Progress" in accordance with the Technical specifications 2272-010-14596226-2003 filaments of polypropylene film. According to these threads are used in the manufacture of twines, ropes, bags. Several kinds of produced yarns were selected filament polypropylene fibrillated film untwisted. Polypropylene is chemically resistant and good electrical insulation material. Its electrical properties are virtually unchanged even after prolonged soaking in water, and the dielectric constant is little dependent on frequency and temperature. The dielectric constant of the polypropylene - 2.3; tangent of dielectric loss angle tgδ - (2÷4)·10^-4. For polypropylene is characterized by high resistance to repeated bending, electrical properties it is close to polyethylene and koristama polyethylene - the materials that are used in the cable insulation. This property of the material is polypropylene.

In the present invention is used not just propylene yarn, and fibrillated yarns, which are formed at a certain stage of formation and orientation of fiber extraction. Formed at the same time dense packing of the fibrils are combined in the form of a three-dimensional grid, forming a mesh structure. The use of such threads as aggregate leads to the decrease of dielectric permittivity meerilinga space bounded by the screen. This is explained by the presence in the threads of the cavities, which are filled with air, the dielectric constant which is less than that of the solid dielectric. Decreases the volume of the solid insulation decreases the dielectric constant of the specified space and, consequently, decreases the capacitance of the cable.

However, when designing the cable has arisen another problem. In cables that require increased design flexibility while maintaining normalized level of loss occurs, as already noted, the problem of ensuring the symmetry of the structure. Round cross-sectional shape of the cable and the symmetrical arrangement of the pairs relative to the screen should provide a placeholder. The location of the placeholder, as this is nedosmotrela in the prototype, namely, the twisted pair of conductive wires with threads leading to the ingress portion of the threads between the cores of the pair, which breaks the symmetry of the cable with the corresponding deterioration of the transmission parameters.

The invention provides for the arrangement of the threads longitudinally (along the axis of the cable) and the entire length of the cable between the screen and the insulated conductors of the pair. This helps to ensure the symmetry of the location lived a couple on screen, as well as to increase the distance between the screen and the pair that, in turn, reduces losses in the cable. It was revealed that the magnitude of the capacitance of the cable depends on the location of the placeholder. So, when the twist filler with veins capacity was larger than the longitudinal location along the length of the cable. In this case, we can only speculate and explain it in the following. When the twist in areas where the filler is located between the conductors is compression, which leads to the reduction of air cavities, and this, in turn, is causing increasing dielectric constant, which determines the capacity.

Thus, it is necessary to repeat the task that needed to be addressed to achieve a technical result (getting the cable with the necessary stable electrical and mechanical characteristics), was solved in one constructive element of the m-core. However, a filler with a specific structure made of a specific material and placed in a certain way relative to other elements of the cable. And only use all three of these characteristics contributed to these characteristics.

Thus, the set of essential features that ensure the achievement of identified technical result and expressing the essence of the invention is as follows.

Symmetrical high-frequency cable includes a core formed insulated polyethylene or porous polyethylene electric conductors, twisted together in a pair, and a filler disposed between the insulated conductors and the shield, on top of which is a shell. The filler used fibrillated polypropylene film untwisted strands, spaced throughout the length of the cable longitudinally.

The invention is illustrated by drawings.

Figure 1 shows a photograph of threads deployed to demonstrate patterns in longitudinal and transverse directions.

Figure 2 shows a photograph of the sample symmetric high-frequency cable with a partially deleted (the length of one pitch of the pair) screen and shell. One has lived colorless (clear) insulation, through which is seen the conductive core. Polypropylene yarn lane on the day the plan split the sample before the shooting were separated to illustrate the construction of the cable.

Figure 3 shows the cross-section Troparevo cable.

The cable includes a conductive core 1, the insulation of the conductors 2, the aggregate of the two polypropylene fibrillated untwisted yarns 3, the screen is made of laminated aluminum foil 4 and braiding of tinned copper wires 5, the sheath of PVC 6. Also in figure 3 are given the designation of the diameter of the conductors d, the diameter of the conductor insulation (D_fromand external cable diameter D_about. The cable shield can be made of laminated polymer film of aluminum or copper foil, banded braid of tinned copper wires or simply in the form of a dense braid of copper wires. The sheath can be made of PVC or polyethylene or other polymeric material, thereby protecting the cable from external influences.

It had been made two versions Troparevo symmetrical high-frequency shielded cable with a core diameter d=0.65 mm and the diameter of the conductor insulation (D_from=2,3 mm as a filler and in fact, and in another case used two polypropylene fibrillated yarn with a nominal linear density of 1000 Tex. The first option is the placement of the placeholder similar cable design adopted for the prototype, the second - the imp is replaced in accordance with the utility model.

Figure 4 presents the frequency dependence of the attenuation in the cable: curve 1 for cable manufactured according to the first embodiment; curve 2 is for a cable made in accordance with the utility model.

As already noted, the placement of the filler between conductors can lead to asymmetry (capacitive asymmetry) location lived relative to the screen, which in turn leads to a difference in phase velocities of propagation of electromagnetic waves through his veins constituting a pair. Length of test samples cables (for option 1 and option 2) was 50 meters. At a frequency of 130 MHz cable with capacitive asymmetry lived peak is observed growth attenuation factor (curve 1), whereas a cable made in accordance with the utility model has the minimum value of the attenuation coefficient in the entire frequency range.

The characteristic impedance of the cables within the normalized value of 135-150 Ohms.

LITERATURE

1. Belousov NI, Gridnev I.I. Radio-frequency cables. M., "Energy", 1973, str.

2. Belden. Audio / Video cables. European Edition, 1999, p.14, 15.

Symmetrical high-frequency shielded cable containing a core formed insulated polyethylene or porous polyethylene, conductive conductors twisted together in a pair, and a filler made from polymer strands, Raina least part of which is placed between the insulated conductors and the shield, on top of which is a shell, characterized in that the filler is made in the form of fibrillated polypropylene film untwisted yarns, superimposed longitudinally, and the other part is located between the insulated conductors and the shield.