Visual Appearance Identification
1. PVC sheath: The surface can see that there is a regular "unevenness" in the inside of the crimping net, which means that the processing technology is good and no relative slipping 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 network: whether the number of copper mesh is enough to check the weldability, whether the copper wire is scraped inside the tinned copper wire, the hardness of the aluminum-magnesium alloy wire is obviously larger than that of the copper wire, and the mesh is sparse. Inhomogeneous, and the insulation is not tightly wrapped is a poor cable;
3. Check the core: Diameter - SYV cable is 0.78-0.8mm, SYWV cable is 1.0mm; Recently there is a SYV75-5 core cable diameter of 1.0mm, 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 insulation layer: Cut the insulation layer obliquely, and pull the core wire in the peeling direction to see if the core wire and the insulation layer are covered with the process material; good cable has a large sealing force and is poor The cable is not covered;
5. Longitudinal tensile test: take one meter cable, peel off the core layer, insulation layer, shielding layer, and outer cover, and leave 10cm long. The method is: two hands hold the adjacent two layers of the cable, pull in the opposite direction; good cable generally can not pull force, poor cable can be easily pulled out without much effort - elevator cable is very important, many so-called "Elevator special cable" has this problem.
Test with fire
General fake copper wire: copper clad aluminum, copper clad aluminum alloy, copper clad steel, copper clad iron.
High imitation of fake copper wire: copper strands in a certain proportion of copper strands are added to the aluminum-magnesium alloy. After other materials are processed by electroplating copper, the general price is more expensive than the previous one. After all, there is true copper in it.
Non-complying copper wire: The material is not drawn copper wire made of oxygen-free copper, transmission performance is not good, or the number of cores is not enough.
If at the time of purchase, you forget the classification of these three types of fake copper wire, you can also try the following method:
As the saying goes, gold is not afraid of fire. True or false SYV, RVV and other copper wires can also be used to identify the authenticity of the fire. First, we can open a line to reveal a piece of copper wire and sparsely distribute them (which is better). The windproof lighter is generally used to burn, it will appear. The real copper wire is very resistant to high temperatures. There is absolutely no problem in one minute or more. At most, the color will become a little bit more; if it is a copper-clad aluminum, copper-clad aluminum-magnesium alloy will soon bend down; if it is a copper clad steel, copper report After the iron was burned, it was shaped with a knife.
Transmission performance test
1. Color camera video signal can be used as "standard video signal source": The camera video output for test engineering should be 1Vp-p on a 75 ohm load, that is, from the bottom of the horizontal synchronization head to the highest white level of the video signal. “Peak-Peakâ€; Note that the amplitude of the horizontal synchronization head is “-0.3Vâ€, the amplitude of the color burst head (4.43M sine wave pulse) is 0.3Vp-p; select the oscilloscope sensitivity, and hit the amplitude calibration status. Select a camera with better indicators as a "video source";
2. Test the cable as long as possible to reduce the measurement error, such as 1000 meters, the cable middle connector must use "F-type connector" and coaxial double-pass (cable equipment), do not use welding method, because the welding method destroys the cable Continuity of coaxiality and characteristic impedance.
3. The DC resistance of the measuring cable data: SYV75-5 cable as 1000 meters, the DC resistance of 35-40 ohms core, the outer shielding layer to 24-36 ohm resistor 1000 m (eds several different shielding layer, a large resistance difference) SYWV75-5 cable 1000 meters, DC resistance core wire is 18-22 ohms, external shield resistance 1000 meters is 24-36 ohms; Accumulation of this information is very useful, not only can judge the quality of cable material, but also used to engineering The inspection of the quality of the wiring and the pipe is performed. When the pipe is worn by a person, the line is broken, the resistance value becomes large, the video signal becomes weaker, and the interference that should not occur also appears. This type of “accident†has a very high probability of occurrence. Often overlooked.
4. Measure the high and low frequency attenuation characteristics of the cable : Measure the amplitude of the line head and burst head at the end. Calculate the attenuation with 0.3V as the 0db reference. The line head represents the low frequency attenuation and the color burst represents 4.43M high frequency attenuation. .
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