1. PVC sheath: The surface can see the regular 'unevenness 'of the woven net inside the compaction, indicating that the processing technology is good and will not produce relative sliding, which is a good cable;
The appearance is smooth, and the 'unevenness' of pressing the woven net cannot be seen. The sheath is loose and dynamic by hand, which is a bad cable.
2, check the shielding layer weaving: whether the number is enough, copper woven net, check the weldability, tinned copper wire scraping to see if it is copper wire, the hardness of aluminum magnesium alloy wire is significantly greater than copper wire;
The network is sparse, the distribution is uneven, and the insulation layer is not tight. 3, check the core wire: diameter---SYV cable is 0. 78 to 0. 8mm, SYWV cable is 1. 0mm; Recently, a SYV75-5 Core diameter is 1.
0mm Cable, the characteristic impedance of this cable, is definitely not 75 ohms and should not be used in 75 Ohm transmission system.
4. Check the adhesion force between the core wire and the insulation layer: cut the insulation layer obliquely, pull the core wire according to the peeling direction, and see if there is any bonding process material between the core wire and the insulation layer;
Good cables have large adhesion force, while poor cables do not. China wire and cable network www. Xianlan315.
Com longitudinal tensile test: take one meter of cable, strip the core wire in layers, and leave the insulation layer, shielding layer and outer sheath 10 cm long each.
The method is: hold the two adjacent layers of the cable with two hands respectively and pull in the opposite direction;
Good cables cannot be pulled with general strength, while poor cables can be pulled out easily without much effort.