Sealed and balanced high-frequency cable

FIELD: data transmission under very humid conditions, those including on board ships.

SUBSTANCE: proposed cable has sequentially arranged core incorporating at least two pairs of polyethylene covered stranded conductors, filler in the form of low-molecular rubber based sealing composition, shield, and sheath with mentioned filler in-between. This composition is, essentially, compound incorporating 100 parts by mass of rubber SKTN and 3-5 parts by mass of catalyst; the latter has 7 mass percent of γ-aminopropyl triethoxysilane and 93 mass percent of ethyl silicate; these pairs are placed longitudinally throughout entire cable length inside filler All air gaps are filled up (no water penetrates along cable).

EFFECT: reduced outer diameter at low attenuation constant and high near-end cross-talk attenuation throughout entire operating frequency band.

1 cl, 2 dwg, 1 tbl

The invention relates to one of the branches of the electrical industry - cable technique, and more particularly to a symmetric RF tight shielded cables for data transmission. The following cables are used to organize the transmission of digital signals in communication systems and control automated processes on ships, on sites requiring high integrity and protection against the penetration of water through the cable. Due to the specifics of the installation and operation of cables on ships, their design must have high flexibility (low bending radius), the minimum dimensions (outer diameter of the cable) in combination with the minimum achievable level of losses (attenuation factor). In addition, the use of sealed cables must assume technological ways of removing a protective sealant on the end of the cable during installation of the connector.

Known low-frequency sealed shielded cables containing a core formed insulated electric conductors, twisted together in pairs, placed in a shared screen and the casing, the sealing composition of hydrophobic low-molecular weight fractions of refined petroleum products, filling the space core [1]. This design sealed cable has at low frequencies with Abilene electrical parameters, high flexibility and does not create problems during installation. However, this type of filler has properties vascodagama "wazeliniarzy" mass and the maximum longitudinal water pressure, which can withstand such a cable, typically less than 10÷15 ATM, whereas for marine cables are required to provide resistance to longitudinal pressure of not less than 60 ATM.

Known symmetric RF tight shielded cables containing consistently located core, including twisted pairs insulated with polyethylene conductive wires and sealing the filler on the basis of low-molecular rubber, screen sharing, and a protective shell. Thus over each pair of insulated conductors imposed total isolation from polyethylene and braid of tinned copper wires. Thus, the core includes twisted among themselves individually shielded pairs. As aggregate is used a rubber composition based on silicone rubber.

This design allows a small longitudinal leakage of water at a maximum pressure of 100 kgf/cm²has large dimensions (outer diameter), resulting in increased installation bending radius, increases the amount of cabling on the courts, but also complicates its cutting during installation.

Systems is Amy cable has the basic electrical characteristics (crosstalk, the attenuation coefficient, the wave resistance), satisfying the consumer, and essential features is the closest analogue to the cable in accordance with the invention [2].

The problem to which the invention is directed, is the creation of a high-frequency symmetrical cable, ensuring reliability and stability of the electrical characteristics of the circuits in conditions of high humidity, in particular, on boats, at the minimum possible size (outer diameter).

Before talking about the technical result obtained by carrying out the invention, it is necessary to analyze the relationship between the structural elements of the cable and its characteristics.

The main parameters of the transmission of high frequency electrical signals on symmetric multi-pair cable are: the attenuation factor of the signal in the pair, the characteristic impedance of the pair and crosstalk induced signal of two adjacent pairs (crosstalk near end). The attenuation coefficient characterizes the reduction of electromagnetic energy signal when the distribution by cable. The reduction or attenuation of energy due to her loss in the transmission line. Part of the energy consumed in the conductive veins, screens and dielectric - mergelina space. Even some part of what the power can be lost due to capacitive asymmetry lived in relation to the cable screen. If the cable symmetry pairs are provided, the level of attenuation factor is set by appropriate choice of material, design and diameter of the conductive wires and the insulating material of the conductive wires. The level of losses in the cable increases with individually shielded pairs. The wave resistance of the cable is also a normalized value for the considered symmetric cables set the appropriate selection of the thickness of the insulating layer that defines the distance between the electric conductors of the pair.

The mutual influence of two adjacent pairs of cable on each other is characterized by a transient attenuation near end, and the more the absolute value of this parameter, the better protected transmission chains (pair) from mutual (parasitic) interference. The magnitude of crosstalk is achieved by use of possible design solutions:

- shielding separate couples;

- selection of different (nonmultiple) steps twisting adjacent pairs;

- diversity pairs relative to each other as possible distance with the help of special items (profiles, Cordele)introduced into the composition of the cable core.

To increase crosstalk can be used as one of these solutions and their possible constructive combination of the project depending on the totality of the final requirements, requirements for cable. Typically, a generic requirement to develop the cables is reduced to the need to achieve the highest possible electrical parameters of the transmission signal) of the smallest possible size (diameter) of the cable. Reducing the size of the cable, respectively, reduces mounting the bending radii of the cable, to reduce the amount of cabling in the courts.

Because the cable works in conditions of high humidity, in particular, on ships, first of all it was necessary to ensure its integrity.

Sealing filler in varying degrees, affects all the main characteristics of the cables. While this influence depends on the components used in the composition forming the filler and its physical condition.

In the present invention for sealing was used compound. It is known that compounds as compositions that do not contain solvent, which at the time of application at normal or elevated temperatures in a liquid state and hardening after application in the cooling or occurring chemical processes, ensure a reliable sealing of electrical products. Advantages has a compound based on a low molecular weight silicone rubber SCTN - organosilicon compound. To any who are: heat resistance, high electrical insulating properties, continuing to 250-260°C, low vlagopoglascheniem, manufacturability, low toxicity. Silicone rubber compounds remain elastic and electrical properties at temperatures up to -60°C. Caulk compounds mechanically strong, have a good benzo-, oil - and water-resistance. It organosilicon compound type Sealers PC-68 (TU 38.103508-81) was used in the development of cable according to the invention.

The specified compound contains:

low molecular weight rubber SKT - 100 parts by weight and the catalyst in an amount of from 3 to 5 parts by weight, which consists of γ-aminopropyltriethoxysilane - 7 wt.% and ethyl silicate - 93 wt.%. Thus, the amount of catalyst taken in the specified range from 3 to 5 parts by weight, as follows from the above THAT, does not affect the characteristics of the compound. Therefore, the amount of catalyst taken in the specified range, does not affect the settings of the cable (which was confirmed by the experimental data).

The compound when injected into the cable forms a soft and supple padding and has the following characteristics: conditional tensile strength - 0.25 MPa, the elongation at the moment of rupture is 70%, the tangent of dielectric loss with frequency of 10⁶Hz does not exceed 2.5·10^-3whose dielectric constant is not more than ,0.

Despite the fact that the compound possesses all the characteristics necessary for the protection of products, working in conditions of high humidity (able to form a soft elastic padding and consistency which allows a good obwolakiwati the cable elements), it does not provide full continuity of the traditional filling cable core, in which the pairs are twisted together. Between pairs remain small air gaps that are not filled with compound. This is confirmed by experimental data obtained in the determination of the longitudinal water infiltration. So, when testing two metre samples chetyrekhmernogo cable, at the end of which was created hydrostatic pressure to 100 kgf/cm²observed longitudinal seepage of water up to 45 cm³within 2 hours. To eliminate this drawback unshielded pair placed inside the compound longitudinally along the length of the cable. The consistency of the compound allowed to freeze the selected location pairs and fill in any air gaps in the core, and between the screen and the shell, and the seepage of water along the cable was almost absent (see table).

In cable design no individual screens for each pair that led to its simplification and, as a consequence, the reduced outer diameter of the cable is twice which in turn provided a small bending radius and convenient technology cutting ends of the cable, and also to reduce the amount of cabling in the courts.

No individual shielded pairs should lead to a reduction in crosstalk, one of the most important characteristics of symmetric high-frequency cable. However, as already noted, the increase in crosstalk can be achieved by passing pairs relative to each other with the help of special items. In this case, this element can be considered a compound, which, having certain physical characteristics, fixes pair at a desired distance.

From the above we can conclude that the utility model provides a few technical results: good sealing in the filling all air gaps sealing filler, small size (the outer diameter is two times less than in the prototype) while maintaining the basic electrical characteristics: low coefficient of attenuation and high values of the crosstalk at the near end in the entire operating frequency range.

The set of essential features sufficient to achieve provided by the invention the technical results, the following: symmetrical high-frequency hermit CNY cable contains consistently located core, including at least two pairs of twisted among themselves isolated polyethylene conductive wires, the sealing filler formed by composition based on low molecular weight rubber, screen protective shell, between which is also a placeholder. When this composition is a compound containing low-molecular rubber SKT - 100 parts by weight of catalyst is from 3 to 5 parts by weight, which consists of γ-aminopropyltriethoxysilane - 7 wt.% and ethyl silicate - 93 wt.%, and the pair are located inside the placeholder longitudinally along the length of the cable.

The practical realization of the invention in the manufacture involves the application of compound pairs for which they are first passed through a container of the compound, and then through calibers with holes, the arrangement of which corresponds to the desired placement of the pairs in the cable. The design of the gauge depends on cable settings, in particular the diameter of the insulated conductive wires and the number of couples. Have conducted a large number of technological samples and identified the experimental dependence, which reflects an ideal location pairs relative to each other and presupposes a certain distance (gap) between them. As the size of the gap is relatively small (within tenths of a millimeter), the ideal p is polozenie pairs almost impossible to get. Cable - lengthy product, and when the output pairs of the caliber of the distance between them may vary in one direction or another. Tests of prototypes of the cables showed that the essential feature is the location of the pairs of longitudinal (rather than twisting them, as is done in the prototype), while even the contact pairs at specific points along the length of the cable does not lead to the violation of his integrity and the increase of the outer diameter. May be somewhat reduced crosstalk cable (which depends on the distance between pairs), but noticeable changes this option was not checked.

Thus, the tests confirmed that the previously identified set of essential features is sufficient to solve the task of achieving technical results - get sealed cable and reduce its size while maintaining the proper level of its electrical parameters.

The invention is illustrated in the drawing, in which figure 1 shows a cross section chetyrekhmernogo cable. The cable contains a pair of insulated conductive wires 1, the sealing filler 2, screen 3 and the shell 4. The conductors may be solid or stranded. Isolation lived made of polyethylene. The screen is made of aluminum or copper foil, laminated polymer plank the th, either in the form of a braid of copper wires. The shell can be made of PVC or polyethylene or other polymeric material, thereby protecting the cable from external influences.

Manufactured in accordance with the invention, the design chetyrekhmernogo sealed symmetric high-frequency shielded cable, marked under the brand Citifm 4×2×0,52, shown in the photograph (figure 2). Figure 2 pairs indicated by figure 1, the sealing compound - 2 shield - 3 and the protective shell 4. Comparison of the main parameters of the utility model and cable brand KWACH 4×(2×0,5)e selected as the prototype [2], shown in the table. From the given data achieved technical result is obvious: the invention has half the size (and therefore allowing half the radius of the circuit bends) and the best tightness at almost the same level of electrical parameters.

Sources of information

1. Parfenov Y.A. telecommunication Cables. M., 2003, p.35, 36.

2. C - 186-2002. Cables combined sealed, p.1-8.

Symmetrical high-frequency sealed cable containing sequentially spaced core comprising at least two pairs of twisted among themselves isolated polyethylene conductive wires and sealing the filler formed by composition based on low molecular weight rubber, screen protective shell, between which is also specified filler, wherein the composition is a to impound, containing 100 parts by weight of low-molecular rubber SCTN and 3-5 parts by weight of a catalyst consisting of 7 wt.% γ-aminopropyltriethoxysilane and 93 wt.% ethyl silicate and vapors are located inside the placeholder longitudinally along the length of the cable.