Inductive stylus and digital multimeter are available;
Adapted to cables without metal armor and steel strip shielding;
Pay attention to prevent electric shock, the test station and the terminal connection when rewinding the equipment.
When there is a metal armor layer such as a copper strip or a steel strip outside the cable, the induction method cannot be detected. In this case, the capacitance method is used; it is suitable for all cables; when using the capacitance method, the principle of the capacitance test is first understood - when testing the capacitance, The AC/pulse signal is used in the test loop, that is, the AC voltage divider is measured or the capacitor body (two mutually insulated metal poles) is charged and discharged, and the accumulated power on the capacitor body is tested and converted into a capacitance reading.
Capacitance method, which may be caused by the winding of the cable, the inductance of the insulated cores, the resistance of the non-conductor (such as steel strip), the stray capacitance between the conductors, etc., affecting the accuracy; The inductance is small, can not be counted; the resistance has little effect on the measured capacitance, but the difference between the conductor and the steel strip connection and the unconnected capacitance is not large, but it can be ignored, but the stray capacitance has a great influence, and a test is done. : The capacitance between the intact core and the steel strip is 117nF. The other cores are connected to the steel strip. The result is still 117nF, and there is 72nF between the two cores.