The good and bad identification of the video line, the real detection is the need for special equipment and instruments. And these equipment and equipment are not available in the design and engineering units. In engineering practice, how to identify the quality of the video line:
First, visual appearance identification:
1. PVC sheath: the surface can be seen to compress the regular “unevenness” inside the network, indicating that the processing technology is good, and it will not produce relative sliding. It is a good cable. The appearance is smooth and can not see the “unevenness” of compressing and compressing the net. It is loose with the hand kneading and the cable is bad.
2. check the screen layer network: does the number are enough? Copper wire netting, checking weldability, tin plating copper wire scraping to see whether copper wire is inside or not. The hardness of Al Mg alloy wire is obviously larger than that of copper wire, and the mesh is sparse, uneven distribution, and the insulation layer is not tightly wrapped.
3., check the core wire: diameter SYV cable is 0.78-0.8mm and SYWV cable is 1.0mm. Recently, a cable with diameter of SYV75-5 is 1.0mm, and the characteristic impedance of the cable is definitely not 75 ohms, which is not applied to 75 ohm transmission system.
4. check the adhesion between the core wire and the insulating layer: slit the insulation layer, pull the core line according to the direction of stripping, see whether the core wire and insulation layer are coated with process materials; the good cable has greater adhesion force, and the poor cable is not touched.
5. longitudinal tensile test: take one meter cable, strip off the core line, insulation layer, shield layer, outer household sleeve, each stay 10 centimeters long. The method is: two hands grip the cable two adjacent layers, pulling in the opposite direction; cable general strength pull cable difference without much effort you can easily pull out the elevator cable this one is very important, many of the so-called “elevator cable” has this problem;
Two. Transmission performance test:
The video line, as its name implies, is a transmission line used to transmit video signals. Since the transmission of video signals, at the very least, we should understand the transmission characteristics of the transmission line in the 0-6M band, or, in other words, the transmission performance. Here, we mainly talk about “oscilloscope measurement method”, for reference, because oscilloscope is one of the necessary weapons for engineering contractors, and is one of the necessary inspection equipment for qualification review. The following narration is based on the ability to use oscilloscopes skillfully.
1. color camera video signal can be used as a standard video signal source: camera output test project, in a 75 Ohm load amplitude is 1Vp-p, namely the synchronization head bottom to the white level video signal the highest peak – peak “; that the synchronous head range” -0.3V “color synchronization head (4.43M sine pulse) amplitude is 0.3Vp-p; select oscilloscope sensitivity to amplitude calibration. A better camera is selected as the “video source”.
2. test cable to take a little longer to reduce measurement errors, such as 1000 meters, some cable joints with “F connector and coaxial double pass (CATV), welding methods do not use, because the continuous welding damages of the coaxial and characteristic impedance of the cable.
DC resistance data of 3. measuring cable: SYV75-5 Cable 1000 meters, the DC resistance core wire is 35-40 ohms, outer shield resistance 1000 meters is 24-36 ohms (shielding layer number of series resistance, big difference); SYWV75-5 Cable 1000 meters, the DC resistance core wire is 18-22 ohms, outer shield resistance 1000 meters 24-36 ohm; accumulation of this information is very useful, can not only determine the quality of timber and used for cable, wiring, pipe engineering quality inspection, such as Gu people wear tube, the wires, the resistance becomes large, the video signal is weak, the interference also appeared, this kind of accident occurred the probability is very high, but often overlooked;
4. measuring cable of high frequency and low frequency attenuation characteristics: at the end of measuring head head and color synchronization range, with 0.3V as 0dB benchmark, the calculation of attenuation, the line with the department head on behalf of low-frequency attenuation, color synchronization 4.43M high frequency attenuation, such as: the measured 1000 0.15V synchronization lines, calculated in accordance with the 20log number dB attenuation multiple “-6db/1000m”, the amplitude measured 4.43M color synchronization 1000 meters after attenuation is 30mV, which is 1/10 times the attenuation of -20db/1000m; this method can accurately grasp the transmission quality of different cables, and the “frequency distortion (low and high frequency attenuation difference) with the intuitive notion of difference you can be the same type and structure of the SYV and SYWV cable measured accurately and the performance, compare the difference of products from different manufacturers and the performance, also can compare the changes of different batches of products in the same factory To;
The above 5. methods can also test equipment performance and video transmission system: transmission characteristics such as engineering in every way coaxial video cable, transmission characteristics of optical transceiver (can be measured is good or bad, do not think so, ideal) transmission characteristics of RF transmission, microwave, twisted pair transmission characteristics, distribution characteristics of video distributor, switch the characteristics of the host matrix, we must pay special attention to when the multi output switch at the same time the same input signal, if the switch number more attenuation is large, is wrong, should be the same, you will have a lot of test unqualified products;
6. observation field signal, see the field synchronization position distortion is not big (flat) – should be very flat;
At the same time also can be used for low frequency interference oscilloscope: such as the field signal has slow fluctuation, 50/100 week interference, there are a lot of “grass” beats, mostly frequency harmonic interference, the remote camera is disconnected, the far end of the cable outer conductor short circuit, in the end can directly observe the interference waveform and intensity with the oscilloscope; the method can also check the performance test and real anti jamming equipment.
The main products of Shenzhen Haiwei Video Technology Co., Ltd. in the field of image coding and transmission are HD video encoder, HD video decoder, 4G wireless video encoder, etc., supporting HDMI/SDI/.
VGA/CVBS/DVI/YPBPR HD encoder supports Android APP/ three stream / real-time preview, support /4 4G/1 Road, /8 Road, /16 multi support structure, portable /1U/2U/3U server, the protocol of /HLS/SDK, the industry’s most complete product model, as a broadcast platform, hotel, hospital, school, education and other related broadcast live video codec program provides the perfect solution plan
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