SU737843A1 - Device for measuring electric capacitance of cable cores and wires - Google Patents

Description

The invention relates to chimetering technology and can be used in the cable industry to control the quality of plastic insulation applied to cable Zh.LSY and wires during their production,.

Devices are known for controlling the electrical capacitance of a cable product cores, containing an empty conductive fluid filled dielectric tube with a metallized outer surface. Inside the tube there passes a measurable core, the current-carrying conductor of which forms together with the metallized surface of the tube a cylindrical capacitor {.

These devices increase the sensitivity of the measurements. However, they have errors caused by the presence of their own conductivity, which reduces their value in practical application.

The prototype of the proposed device is a device for controlling electrical capacitance per unit length of plastic-insulated wires, in which 5 baths water is used to ensure electrical contact between the measuring electrode and the surface of the wire, where the wire cools down after applying the insulation.

The device consists of a converter, the measuring and protection electrodes placed in the insulation, and an AC bridge measuring the deviations of the capacitive component of the converter's impedance from a predetermined nominal value 2.,

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The disadvantage of this device is that it is due to the intrinsic conductivity of the converter, which is complex and depends mainly on

20 values of specific electric conductivity of water.

The purpose of the invention is the elimination of errors from its own conductor G1 converter.

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The goal is achieved by the fact that a device for measuring the electrical capacitance of cable cores and wires, containing an ac measuring bridge, is out of 737843

The measuring diagonal of which includes a phase-sensitive indicator and converter containing a measuring electrode that covers the measuring core and is connected to one of the arms of the measuring AC bridge, guard electrodes that cover the measuring core are galvanically connected to the screen and connected to the measuring diagresha AC bridge, equipped with a compensation electrode, which covers the measuring core and is connected to the shoulder of the AC measuring bridge, opposite to echu, in which the measuring electrode.

The compensation electrode is cylindrical with an internal diameter of-. rum, equal to the internal diameter of the measuring and guard-electrodes.

The compensation electrode is located between the measuring electrode and any of the guard electrodes with measuring and guard electrodes.

 FIG. 1 shows a converter of the electrical capacitance of cable cores and apertures; in fig. Figure 2 shows a circuit for connecting a converter to an AC measuring bridge. . 1 measuring 1, compensating 2 and guard 3 electrodes of the converter are tubular in shape and enclosed in internal insulation 4 enclosed by an electrostatic shield 5. External insulation, b, prevents the screen 5 being electrically connected to the electrically operated electrodes 3 and has a potential

similar in magnitude to the potential of the measuring 1 and compensating 2 electrodes. The compensation electrode 2 is located between the measuring 1 and any of the guard 3 electrodes.

The converter is placed in the bath 7. With water, the measured core 8 with the conductor grounded through the process equipment is located along the axis of the converter.

The converter connects to the measuring bridge circuit as follows. Measuring electrode 1 pod:; transforms into One of the shoulders of Jost ,. A compensating electrode 2 is connected to the opposite arm. A reference capacitor 9 of variable capacitance balancing the bridge circuit can be connected either to the shoulder of the AC measuring bridge connected to the compensation electrode 2 with the length of the compensation electrode smaller than the measuring electrode, or to the shoulder, connected to the measuring electrode with a length of a compensating electrode electrode that is longer than the measuring electrode. The guard electrodes 3 are connected between the sample resistances U and 11 of the measuring bridge AC and; 1, the potentials are the same. A working frequency generator 12 is connected to the supply diagonal of the bridge, between model resistances 10 and 11. The phase-sensitive indicator 13 is included in the measuring diagonal of the bridge.

The device works as follows.

When a measured core 8 is placed in the converter, the capacitors formed by measuring 1 and compensating, 2 electrodes and current-carrying conductor of core 8 and distributed over lengths corresponding to lengths of measuring and compensating electrodes are converted into concentrated values, the smaller of which is subtracted from the larger by means of measuring lust alternating current and fixed phase-sensitive indicator 13, configured so that it responds only to changes in the capacitive component of the difference t Cove bridge arms. At the same time, the subtraction of the own conductivities of the measuring 1 and compensating 2 electrodes occurs. Since the values of these conductivities are equal, the difference between the currents caused by their own conductivities is always zero.

The proposed device eliminates inaccuracies from the intrinsic conductor of the transducer inherent to known devices of this type, and excludes both systematic and random components of the error.

The value of the intrinsic conductor of the converter does not depend on the length of the measuring electrode, but is determined by the internal diameter of the electrodes, the length of the guard electrodes and the distance between the guard electrodes and the ends of the converter adjacent to them. A significant increase in the length of the guard electrodes and the distance from the guard electrodes to the ends of the converter, although it reduces its own conductivity, but makes the converter bulky and inconvenient in operation. The introduction of a compensation electrode, the intrinsic conductivity of which also does not depend on its length, allows for insignificant. by increasing the total length of the equipment, it is fully compensated for its own conductivity.

The diameter of the compensation electrode is chosen equal to the diameter of the measuring electrode. Compensation of the intrinsic conductivity of the transducer is also possible with different diameters of the measuring and compensation electrodes; only a corresponding difference in the length of the guard electrode and the distance to the end of the transducer adjacent to the measuring and compensation electrodes is necessary. However, in this case, the converter becomes inconvenient for operation: refueling of the core is made difficult, dirt accumulates at the junction of the electrodes;

The insulating gaps between the electrodes are made smaller than the diameter of the electrodes. This is necessary to obtain a uniform field near the measuring and compensating electrodes.

The measuring electrode can have a length both longer and shorter than the length of the compensation electrode, and the internal diameter of these electrodes, the length of the guard electrodes and the distance from the guard electrodes to the adjacent ends of the converter should be the same. In this case, the mutual compensation of the intrinsic conductivities, equal to each other for both the measuring and compensating electrodes, occurs, and the capacity of the conductor for the wire is measured at a length equal to the difference between the effective lengths of the measuring and compensating electrodes.

In the manufacture of the converter, there may be violations of the equality of the internal measuring and compensation electrodes, the equality of the distances between the measuring electrode and the adjacent end of the converter on the one hand, and also between the compensation electrode and the adjacent end of the converter on the other hand. This causes some systematic component (Inherent errors of the converter. If the specific electric conductivity of the water fluctuates within the length of the converter and the diameter of the measured core changes, then a random component of the error occurs. To eliminate these errors, the guard electrodes are stored in the converter.

The introduction of a tensation electrode and the preservation of the guard electrodes in the design of the converter allows one to eliminate both systematic and random components

the errors due to intrinsic conductivity of the Grouter caused by changes in the specific electric conductivity of water, its level and temperature, changes in the diameter of the measured core and dielectric constant-insulation of the converter, as well as inaccuracies in the manufacture of the converter.

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Claims (3)

1. A device for measuring the electrical capacitance of cable cores and wires, containing the measuring 5 AC bridge, in the measuring diagonal of which a phase-sensitive indicator is included, and a transducer containing a measuring electrode, which covers the measuring core and is included in one of the Lelec measuring AC bridge, guard electrodes, which. covers the measuring core, is galvanically connected to the screen and connected to the diagonal supply 5 variable-current bridge, current., Characterized in that, In order to determine the measurement error from the converter's own capacitance, it is equipped with a compensation electrode that covers the measuring core and is connected to the arm of the AC measuring bridge opposite to the arm into which the measuring elec- tron is connected. 2. The device according to claim 1, which is based on the fact that the compensation electrode is made cylindrical with an internal diameter equal to the internal diameter of the measuring and guard electrodes. 3. The device according to PP, 1 and 2, more so that the compensating electrode is located between the measuring electrode and any of the guard electrodes coaxially with measuring and security electro, dami. Sources of information taken into account in the examination 0 1. Author's certificate of the USSR 313176, cl. G 01 R 27/02, 1971. 2. Сап ±) г1еЕ R.D. ControEting Extrusion of Foam PC. Eeectronices, 18, 1955, No. 4, p. 144