In wire and cable, the resistance of DC resistance and insulation resistance is usually tested. This method is used to judge whether the wire and cable products are qualified. How to make correct measurement of DC resistance and insulation resistance? The measurement methods of these two kinds of resistors are analyzed as follows: 


First, the insulation resistance detection in wire and cable.
The insulation resistance detection of wire and cable generally adopts the voltage and current method, also known as the high resistance meter method. Some wire and cable have a metal protective cover and have a certain shielding function. For the insulation resistance measurement of such a wire and cable, the insulation resistance between the conductor and the metal sleeve or the shielding layer or the armor layer is mostly measured; and for the metal-free sheath Wire and cable, when measuring the insulation resistance value, the wire cable to be tested must be immersed in water, and then the insulation resistance between the conductor and the water should be measured, and the test sample should be kept in line with the water temperature.
 
The insulation resistance measurement value of the wire and cable must be converted into the insulation resistance value per kilometer. Unlike the DC resistance, the insulation resistance value is inversely proportional to the length of the wire and cable; the measurement voltage of the low-voltage wire and cable insulation resistance detection is 100V. , 250V, 500V and 1000V, of which 100V and 500V detection voltage is widely used in the quality inspection department.
 
Second, the DC resistance detection in wire and cable.
At present, the relevant domestic departments usually use the bridge method and the current method to determine the DC resistance of the wire and cable. The measurement method of the bridge method is relatively narrow, and can be divided into a one-arm bridge method and a double-arm bridge method. When the resistance value of the wire and cable is about 1 or more, the one-arm bridge method is adopted. The current method, also known as the micro-ohmmeter method, is based on the resistance value of the wire and cable, using a constant current source to output different constant currents, and then accurately measuring the voltage across the cable under test, the measured data according to Ohm's law, the calculation can be used to obtain the DC resistance of the tested wire and cable. The current method can output different currents, so the measurement range is relatively wide.

The DC resistance and the insulation resistance can be measured well by the above two methods. However, with the advancement of technology, these two methods are slowly being replaced by other precision measuring instruments. These precision instruments provide data with higher accuracy and stability. These data can be used to judge whether the wire and cable products are qualified.