KR820000376B1 - Methods of and apparatus controlling capacitance unbalance-to-grourd in cables - Google Patents

Abstract

Capacitance unbalance-to-ground between conductors of a twisted pair, each of which may be insulated with at least a layer of cellular plastic insulation, is maintained within acceptable limits by controlling the extrusion of the insulation to maintain the measured coaxial capacitance and associated outside diameter of the insulated conductors within a range of values which correspond to acceptable capacitance unbalance-to-ground values.

Description

How to Control Unbalanced Ground Capacity in a Cable

1 is a cross-sectional view of a conductor in which a porous plastic insulator is injected around it in one layer.

2 is a cross-sectional view of a conductor insulated with a porous plastic insulating layer inside and a solid plastic skin layer outside.

3 is a schematic illustration of a cross section of a pair of stranded insulated conductors in a shielded cable and a method of measuring capacitance for the insulated conductors.

4 is an elevational view, partially schematic and partially schematic, of a device implementing the principles of the present invention for coating a conductor with a porous plastic insulator having the ability to detect application.

5 is a graph of the outer diameter vs. coaxial capacitance of the coincident value of five insulated conductors, showing the corresponding capacitive unbalanced ground value between one of the four and four conductors having nominal characteristics.

6 is a graph of the outer diameter versus coaxial capacity of an electrothermal conductor mathematically related to the outer diameter and coaxial capacity and having a line of double fixed mutual capacitance and fixed capacitance unbalanced ground.

7 is a graph of the outer diameter versus coaxial capacity of an insulated conductor having two different operating windows.

8 is a schematic representation of the wheelback control of the device of FIG.

The present invention relates to the control of earth unbalanced capacitance in cables, in particular to the control of earth unbalanced capacitance of stranded conductor pairs insulated with at least one porous insulator in the cable.

Recently, the gaps between a plurality of insulated pairs of stranded conductors insulated with solid plastic constituting the core of a multipair telephone cable have been filled with a waterproof compound to prevent the ingress of water, which affects the electrical properties of the cable. However, replacing the air in that gap with a waterproofing compound results in worse insulation properties, so the amount of insulation around each conductor must be increased to improve the insulation properties. This results in an increase in the cross-sectional area of each of the insulated conductors with the cross-sectional area of the core, which requires additional plastic components to form a jacket around the core and an increase in manufacturing cost is inevitable. Each conductor insulates the porous plastic covering the outer surface of the solid wear resistant plastic material to realize the advantages of a full cable and at the same time reduce the size of the insulated conductor to maintain a price comparable to that of a full cable. Because the porous plastics have a low dielectric constant and later the more insulating properties of solid plastics, the reduced wall thickness of the porous plastic insulation is insufficient for the total thickness of the porous plastic insulating plastic skin layer of the solid plastic, and the solid in the air core cable It can be used as a result of plastic insulation.

Although perforated plastic insulators are well known in the art, the problem arises in control coefficients where the quality of the insulated conductor is indicated, for example, the coaxial capacity of the insulated conductor and the outer diameter. Coaxial capacitance is defined as the capacitance between a probe and a conductor separated by an insulator. Acceptance agents include methods and apparatus used to control the amount of expanded plastic in the porous plastic and the use of the porous plastic in the conductor to maintain this coefficient in the limit. egg. Serejo and T. s. US Patent Nos. 3,914,357, published October 21, 1975, 3,973,197, published August 3, 1976, and 4,017,228, published April 12, 1977. Lack of control of the amount of expansion, a coefficient that is not commonly encountered in solid plastic insulators, can result in random changes in the dielectric constant of the porous insulator. Random changes in dielectric constant affect the capacitive earthing, for example, by measuring the quality of a conductor in its capacity to prevent an increase in energy from an external source, such as a power transmission line, and a twisted pair of insulated conductors. It is defined as grounding capacity. For example Horn Y. See Vol. 5, Lies A. B., of Boulevard's 1974 call, "A. B. B. of External and Internal Telephone Cables."

After the conductors are insulated with the porous insulator, they are twisted together in pairs and formed in the cable. To be accommodated, the twisted pair of conductors must display different or unbalanced capacitance grounds less than the predetermined value. The experiment results in showing that two phases of a phase have a capacitance ground value that is not accepted by a pair when they are twisted together while each has a coaxial capacity and an outer diameter value of the acceptance. If the measured values of the outer diameter and coaxial capacity of each pair of insulated conductors in the enclosure are limited, capacitive unbalanced ground is also used as accepted. Winddel. a. Seeing the polyethylene insulated telephone cable of the 4th year wire and cable symposium on December 7, 1955, J., this anomalous appearance is overcome by twisting a conductor with the same capacitance ground value. However, this requires expensive price control.

Capacity of insulated conductors less than the prescribed value and the capacity of the insulated conductors to maintain the unbalanced ground value, the capacity of the insulated conductors, respectively, compared to the conductors with selected values of coaxial capacity and external diameter so that the use of insulators on the conductors falls within the range of the prescribed values. This is solved by the present invention, which is sensed to adjust the unbalanced ground.

The method of carrying out the principles of the invention covers the conductor with a plastic insulating material forming the insulated conductor, measures the outer diameter and coaxial capacitance of the insulated conductor, and measures the electrical signal corresponding to the respective connecting diameter and measured capacitance of the insulated conductor. To connect these signals to a capacitive unbalanced ground between each of the referenced conductors and a reference insulated conductor having a predetermined value of outer diameter and coaxial capacitance, and to maintain a capacitive unbalanced ground between the reference conductor and the mentioned conductor within a predetermined range. To control the covering of the conductor. In one embodiment, the generated signal of the coaxial capacitance and the outer diameter is shown on the coincidence line of the continuous recorder and the line of constant constant expansion and other constants of the capacitive ground between the doubled reference conductor and the insulated conductor therein and the outer diameter and coaxial capacitance It is related to the value. It has been found that conductors insulated from the coincident value of the outer diameter and the coaxial capacitance apart from the defining portion of the line having a predetermined range of capacitance unbalanced ground values compared to the referenced conductor are twisted together and a pair of capacitance unbalanced ground values are obtained.

Facility for pushing porous insulation over the conductor to form an insulated conductor The connected outer diameter of the insulated conductor and the facility for measuring capacity, the area defined by the space line of the fixed-capacity unbalanced ground value, and the diameter connected to the corresponding line of constant percent expansion At least a percent expansion of the porous insulation to maintain a consistent value of coaxial capacity and diameter within the defined area, and to the facility showing the measured capacity, the facility to produce a continuous indication of the measured diameter and the connected diameter of the conductors on the municipal facility. There is a device for regulating the capacitive unbalanced ground between the regulating conductors. In one embodiment, the device also has a facility for twisting together conductors with insulators equalized by diameter and capacity falling into the defining region of the line.

Cellular plastic insulator 21 (FIG. 1) is known for enclosing conductor 22, a copper or aluminum wire with a diameter in the range of 0.4064 to 1.1430 mm, and contains a solid plastic material containing mixed expansion media protruding around the conductor. It is formed.

In FIG. 2 there is shown a double insulated conductor 23 comprising a conductor 22 having a concentric layer 24 of cellular insulator 21 and a solid plastic insulator around it. The outer layer 24 is, for example, a thin shell 24 made of a suitable material for the collar, which gives rigid mechanical properties to the insulator, has improved voltage breakdown properties, and reduces and encodes the permeability of the insulator for the filling composite used. It is made of polyvinyl chloride (PVC) or polyethylene forming a. The outer diameter of the insulated conductor 23 varies between 0.7620 and 2.0320 mm and the wall thickness of the outer layer 24 ranges from 0.0508 to 0.1270 mm.

In FIG. 3, two insulated conductors 26 and 27 are shown surrounded by cable shield 28 to illustrate capacitive measurements. To test conductor 26, all other conductors (not shown) in the cable containing conductor 26 and twisted conductor 26 are grounded and the grounding capacity of conductor 26 is measured and labeled Cg ₁ . The grounding capacity Cg ₂ of conductor 27 is measured in the same way to yield the difference Cg ₁ -Cg ₂ . This difference is expressed in terms of unbalanced ground capacity. The capacitance between the two conductors 26 and 27 is denoted C ₁₂ and added to the parallel combination of Cg ₂ and Cg ₂ to obtain the properties mentioned as mutual capacitance. The ground capacitance characteristic of an insulated conductor is a function of the thickness of the insulator, the dielectric constant and the distance of the conductor to the shield. The dielectric constant of the insulator decreases as the percentage void increases, and also the grounding of the cell insulated conductors, as published in a recent paper by Winderer, published in Polyethylene Insulated Cable. Dose value changes.

The term "cell insulator" is not only molded from solid plastics containing a mixed expansion medium, but also includes insulators such as high density polyethylene (HDPE), for example shrinkage voids generally occurring adjacent to conductor 22. It is worth noting that. Although the method and apparatus of the present invention have been described for controlling ground capacitance imbalance in expanded cellular insulators, they are equivalent to conductor 22 insulated with solid plastic insulators, for example, to improve export voids to act as expanded cellular insulators. Is applied.

Insulator 21 protrudes around conductor 22 by means of the device indicated by the number 30 as shown in FIG. The following description of the methods and apparatus of the present invention leads to the inference that conductor 23 is surrounded by cellular plastic material 21 or double insulating layers 24 and 21. It should be noted that the term "plastic" is intended to include both thermoplastic and thermoset materials including rubber and rubbery materials.

Conductor 22 proceeds by capstan 32 through protrusion 31 through which insulator 21 or double insulation layers 21 and 24 are applied by a die (not shown) which may be disclosed and claimed in US Pat. Nos. 3,947,173 and 3,903,233. do. After that, the insulated conductors 23 are drawn out of the projections 31 and the predetermined amount of movement is moved into the cooling vessel 33 through the gap distance indicated by "X". As can be seen in FIG. 4, the cooling vessel 33 is mounted on the gear and rack arrangement 34 to reciprocate longitudinally in the movement path of the conductor 23 so that the voids can be adjusted to control the expansion rate of the cell layer 21.

Two in-line measurements of the double insulated conductor 26 are made near the downstream end of the cooling vessel 33. The capacity monitor 36 measures the coaxial capacitance of insulator 21 or insulation layers 21 and 24 covering conductor 22. The capacity monitor 36 may be of the type shown in US Pat. Nos. 2,765,441 or 2,908,861 or as shown in US Pat. No. 2,804,592. The full diameter do of insulated conductor 23, or the insulator diameter (FIGS. 1 and 2), hereinafter referred to as DOD, is manufactured by, for example, a beta instrument company, the underwater diameter indicated by the model number TG 1000 or TI 500. It is continuously monitored by the same gauge 37 as the gauge. Typical traces of full capacity Co and DOD are recorded on a strip chart art (not shown).

In order to meaningfully display the process change, a coordinate chart recorder 50 (see FIG. 4) of a type commercially available from Hewlett-Packard Company, indicated by model number 7004B, is used. The device 50 has a continuous recording printer (not shown) which is moved up and down by the current signal from the capacity monitor and is moved from side to side by the current signal from the DOD gauge 37. ChartArt 53 is insulated so that changes in coaxial capacity and DOD indicated by the location of a recording press (not shown) correspond directly to incremental changes in coaxial capacity and DOD supported by the respective monitoring devices 36 and 37. Into the device 50 for each reel (not shown) of the conductors 23. Encouraged above ChartArt 53 is the operating window or target area 54 which shows the coaxial capacitance and the appropriate DOD for the insulated conductors 23.

Although it is desirable to use cell insulators in filling cables, there are problems specific to cell insulators that must be overcome. The use of solid plastic insulators to wrap conductor 22 only covers traces of DOD or coaxial capacity and requires an actuator to adjust one parameter such as, for example, projection rotational speed or linear velocity, but with additional parameters. Variables should be taken into account in treating cellular plastic insulators. In order to maintain the coaxial dose-DOD trace for the cell-type plastic insulator within operating window 54, the trace should be matched for production parameters that can be changed by known process parameters. As previously shown in U.S. Pat. It was decided. It is to be understood that "expansion" or porosity means a percentage of the cross sectional area consisting of voids.

Dielectric constants for single cell type insulation layers and double insulated conductors, i.e., the weight and expansion ratio of the insulation per unit length of a double-wound plastic insulation are described in US Pat. Nos. 3,914,352, 3,973,187 and 4,017,228, above. Can be calculated with the equation described. From these equations, the coaxial capacitance values and the values of DOD can be calculated for the weight of the insulating material and for the parallel lines, the constant weight of the insulator extruded in grams per ether, for example, conductor 23, and the constant expansion coefficient. Lines 57-57 are shown on operating window 54. 4 shows the constant expansion rate and constant output seen in the mathematical relationship in the plot of coaxial capacity versus DOD for cell plastic insulation.

Typically, the DODs of the conductors insulated from the coaxial capacitance Co (see FIGS. 1 and 2) are monitored by successive indications in a conventional manner so that diagnostic indications are made with the expansion rate as well as the continuous indication of coaxial capacitance and DOD. The insulator weight per foot of conductor 23 is continuously indicated. By utilizing the principles of the above-mentioned US patents, the operator can consider the lines on the synthetic recording device 50 and make adjustments necessary for calibration.

If protrusions 31 are used, it should be noted that the output of protrusions 31 for epidermal layer 24 does not form an inner cell layer 24 and the thickness of the outer layer 24 is substantially constant. In the case of using the present invention for double insulation, the solid plastic on the cell plastic is uniformly formed at the skin thickness (do-di) / 2 and can be used off-line by a separate in-line monitor. . In addition, the composite dielectric constant of the plastic insulating material can be determined and the total weight includes the weight of the solid insulating layer and the weight of the cell insulating layer. From the machine on the line, all coaxial capacities of DOD and double insulation, which are continuous portions of double insulated conductors 23, are measured.

5 shows the coordinate values of the coaxial capacitance and the DODs for the various examples of conductors 61-65 and when two conductors shown as line segments between the segments are twisted at the same time, as shown above, The difference value of the ground capacitances is shown. If the conductors 61 and 62 or 61 and 65 at the top left and bottom right corner or at the top left and center in the graph are twisted at the same time, the differences in ground capacitances are 0.174pf / m and 0.157pf / m. However, in the case of the conductors 63 and 64 in the upper right and lower left in the drawing, the difference in the grounding capacity is quite high. That is, 1.78 pf / m. Higher ground-capacity unbalance, usually due to proximity between conductors and adjacent power lines, such as a pair of crosstalk losses at current carrier frequencies, is acceptable for each of the conductors 63 and 64 shown in operating window 54, respectively. This occurs despite the DOD values and the allowable coaxial capacity.

In the prior art, in order for two pairs of insulated conductors to have a capacity close to their shields and surrounding pairs, the insulating cylinders on the two pairs of conductors had to have the same size and the same dielectric constant. In addition, it was known that the grounding capacity and coaxial capacity in the cable are not the same, but also related to the linear form, and controlling one is the same as controlling the other. As clearly shown in FIG. 5 and as can be seen above, controlling the coaxial capacitance of each conductor in a pair is the result of not being required for control of this pair of ground-unbalanced capacitance values.

Determination of the unbalanced ground capacitance value between insulated conductors 23-23 can be done graphically. The unbalanced ground capacitance between insulated standard conductor 65 having a nominal value of coaxial capacity and DOD and insulated conductor 23 prepared as described above is calculated by the following equation.

Cub = A (DOD-DODo) + B (Cc-Cco)

Where Cub is the unbalanced ground capacity

A and B are constants that can be determined by curve analysis from experimental data

DOD is the outer diameter including the dielectric of an insulated conductor

DODo is the outer diameter including the dielectric of the standard conductor insulated at nominal conditions, Co is the coaxial capacity of the insulated conductors and Cco is the coaxial capacity of the standard conductors insulated at nominal conditions.

The equation is for example a constant unbalanced ground capacitance value, such as between standard insulated conductor 65 and insulated conductor 23, on a representation of a linear coaxial capacitance versus DOD as shown by line segments 71-71 in FIG. It is used to create a group of curves.

The difference between the ground capacitances of two twisted conductors at the same time is found by algebraically subtracting the unbalanced ground capacitance values between lines 71-71 or interpolated values between the coaxial capacitances and the line segments representing the coordinate values of the DOD. Can be. For example, between the insulated conductor 65 having a nominal value and the twisted pair with the insulated conductor having the coaxial capacitance and the DOD values along the line 71 with the measured value of -1.64pf / m in FIG. The unbalanced ground capacity is -1.64pf / m. The twisted pair of conductors 23-23, each having a coordinate value of DOD and coaxial capacitance, located along the same line segment as one of the segments 71-71, has no difference or zero unbalanced ground capacitance.

For each pair of conductors, represented by the coaxial capacitance and the coordinate values of the DOD, the empirically released equation can be used to calculate the common capacitance. Appropriate curves of treatment may allow to form a group of curves of constant constant common capacity within the sixth figure shown as line segments 72-72. Two insulated conductors 23-23 having a coaxial capacitance and a DOD value appearing along one of the segments 72-72 have a common capacitance between the values indicated on the scale on the left in FIG.

In an embodiment for minimizing the difference in ground capacitance values in accordance with the principles of the present invention, the graph is later defined as shown in FIG. 7 by two voided lines 71-71 of unbalanced ground constant capacitance values. It is provided on the operating window 81. The former boundaries are chosen to allow the result of the unbalanced ground capacitance of the twisted pair if two insulated conductors 23-23 that are twisted simultaneously have falling coaxial capacitance-DOD coordinate values on the boundary lines. .

The upper and lower boundaries of the operating window 81 as shown in FIG. 7 are established to control the common capacitance between the two conductors. If all the conductors that have been heated have values of coaxial capacitance and DOD whose coordinate values fall within the operating window 81, if they are twisted at the same time, the difference in the unbalanced ground capacitance of the two conductors will be allowed. In addition, the operating window 82, which is determined in part by a constant weight of voids 56-56 and has a narrow tolerance, is as shown in FIG. 7 and the maximum unbalance is not exceeded as well as the average unbalance is allowed. It is properly designed as it is.

The second embodiment, which is somewhat limited in manufacturing, requires a conventional control system. Each insulated conductor 23 shall have insulating properties such that its coaxial capacity and DOD do not fall into the larger rectangular operating window 54 and do not fall within the predetermined operating window 81 or 82. Therefore, operating parameters are slightly less needed in a good system. Each conductor rail is associated with a reference conductor having an unbalanced ground capacitance value between them and a preselected process value of coaxial capacitance and outer diameter, and when twisted, the operator is conventional to ensure that the main conductors that are twisted together have a minimum difference to ground capacitance. Use the control system of. This measure is not necessary in a good system with two conductors that go through a window test that must have an unbalanced ground tolerance when twisted together.

It should be understood that the control implemented by practicing the principles of the present invention is a double control. Not only is the maximum unbalanced ground capacitance value controlled to be within tolerance, but also the average unbalanced ground capacitance lower than the maximum value. This is very important when using insulation such as HDPE, which has a small average when the maximum unbalance is not large and unchecked.

Referring now to FIG. 8, how the principles of the present invention can be extended to a feedback control system to automatically control processing. As noted above, coaxial capacity and DOD are measured by capacity monitor 36 and meter 37, respectively. The measurements are supplied as inputs to the X-Y recorder 50 and as inputs to the process control computer and are displayed numerically. The input of the computer 100 proportional to the deviation from the nominal value as determined by the processing content causes the logic of the computer 100 to be generated to represent the necessary calibration signals. For example, these calibration signals are used to change the extruder screw speed or to control the machine 34 to move the coolant 33 and adjust the air cap.

The process control computer 100 includes a design coordinate planner or other conventional coordinate system that can be in the harbor of the Cartesian. In this method, the coaxial capacitance and the sweep line of the DOD are reexamined in relation to the unbalanced ground molten iron programmed into the on-computer using the uniform percent expansion line, the uniform insulator weight line, and the previously referenced equation. When determining the area width for the unbalanced ground capacity value, the measurements to match the coaxial capacity value outside the area allow the computer to control the device 30 to approximate variability to vary the percent expansion and insulation weight per meter, thus changing the coaxial capacity and DOD. Let's do it. Using the X-Y chart-recording mechanism 50 associated with the process control computer 100 allows the operator to observe the process status visually and move accurately by the computer 100.

Claims (1)

In particular in a method of controlling the unbalanced ground capacitance between respective conductors covered with plastic insulation to form insulated conductors as shown in the figures and described herein, and the outer diameter and coaxial capacitance of each conductor measured. Means for generating electrical signals corresponding to the outer diameter and measured coaxial capacitance of the insulated conductor of and the unbalanced ground capacitance between each said conductor and the reference insulated conductor having preselected coaxial capacitance and outer diameter values. Means for associating, and means for controlling a process for covering each conductor to maintain an unbalanced ground capacitance between each conductor and a reference conductor within a predetermined area value.

Images