When there are metal armor layers such as copper or steel tape outside the cable, the induction method cannot be detected, and the capacitance method is used at this time. Suitable for all cables; Understand the principle of capacitance testing when using the capacitor method - when testing capacitors, the AC/pulse signal is used in the test loop, that is, the AC partial voltage is measured or by charging and discharging the capacitor (two mutually insulated metal poles), the accumulated electricity on the capacitor is tested and converted into a reading of the capacitance.

The capacitance method may affect the accuracy due to the inductance formed by the cable wound in a loop, the insulation core wound together, the resistance of the non-good conductor (such as steel strip), and the stray capacitance between the conductors. The inductance in this is small and can be negligible; The resistance has little effect on the measured capacitance, but the difference between connecting the conductor and the steel strip and not connecting the capacitance is not significant, and can be ignored. However, the stray capacitance has a greater impact, and a test is done: the capacitance between the intact core and the steel strip is 117nF, and the other core is connected to the steel strip, and the test result is 117nF, and there is 72nF between the two cores.

For convenience, the cable is assumed to be a 2-core steel tape armored cable, in which 1 core has 1 break point.

Specific practices are as follows:

1. Suspend all insulated core conductors and armor layers at both ends of the cable;

2. Measure the capacitance value of the intact insulated core and the broken insulated core to the steel strip (or the third intact insulated core) at both ends, and record the value; At this time, the capacitance values measured at both ends of the corresponding intact insulation core should be very close to each other; The sum of the capacitance values at both ends of the same broken core should be slightly greater than the capacitance value of the intact insulated core at the same position, indicating that there is only one break point or multiple break points but the distance is very close; If the sum of the capacitance values at both ends of the same broken core is less than the capacitance value of the intact insulated core in the same position, it indicates that there are at least two breakpoints; Note: Theoretically, if there is only one break point or several break points but very close, the sum of the capacitance values at both ends should be greater than the capacitance value of the intact insulated core in the same position, and the amount varies according to the cable, see the theoretical analysis below.

3, according to the capacitance value of the broken core insulation core and intact insulation core is compared and calculated, respectively to get the length of both ends, at this time the length and the actual length may be different, the next step is re-corrected; But with two unarmoured cables, you can't calibrate them.

4, if the sum of the calculated length is greater than the actual length, the extra length value is negative, if less than the actual length is positive; Then value the capacitance value of the insulation core with the broken core, distribute the difference, the divided long section to correct the long section, and the short section to correct the short section, then the actual position of the break point is obtained.

Qingdao Tianxing Cable Co., Ltd. focuses on the production of customized wire and cable manufacturers, main: fire wire and cable, power cable, control cable and other products, exported to more than 40 countries and regions around the world, the annual production capacity of 1 billion yuan. 6000 square meters of storage, standing hundreds of millions of inventory, order demand for rapid distribution and delivery, large prices more favorable. Hotline: 16678668098