To identification the quality of monitoring cable is good or bad, the real test requires specialized equipment and instruments. But sometimes these equipment and instruments are not available in design and engineering units. So we can estimate by the straightforward appearance.
1. PVC jacket: The surface can see the regular "unevenness" of the inside of the net, which means that the processing technology is good, and no relative sliding will occur. It is a good cable. The appearance is smooth, can't see the "unevenness" of the compacted net, and the looseness of the sheath is caused by hand, which is a poor cable;
2, Check the shielding layer network: the number of braiding is enough? Copper wire mesh, check the weldability, tinned copper computer wire scraping to see if it is copper wire, the hardness of aluminium-magnesium alloy wire is obviously greater than copper wire; the braided wire mesh is sparse, the distribution is uneven, and the insulation layer is not wrapped tightly. Poor cable;
3, Check the core: diameter - SYV cable is 0.78-0.8mm, SYWV cable is 1.0mm; recently appeared a SYV75-5 core diameter is 1.0mm cable, the characteristic impedance of this cable is certainly not 75 Ohm, not applied to 75-ohm transmission systems;
4. Check the binding force between the core wire and the insulating layer: Cut the insulation layer obliquely, pull the core wire in the direction of peeling, and see if the core wire and the insulation layer are covered with the process material; good cable has a large binding force, poor The cable is not covered;
5. Longitudinal tensile test: Take one-meter cable, peel the core wire, insulation layer, shielding layer, and outer cover in layers, leaving 10 cm long. The method is: Two hands hold the adjacent two layers of the cable and pull in the opposite direction; the good cable is generally unable to pull the power, but the bad one can be easily pulled out without any effort.