Security monitoring cable knowledge

Security monitoring Common cable types and models distinguish between video cable, RF cable, shielded and unshielded cable, signal cable, control cable, etc. Various models and newcomers are often confused. The following are the differences between several common models:

The difference between RVV and KVV RVVP and KVVP: The line used in RVV and RVVP is composed of a multi-strand thin copper wire consisting of RV wires. The line used in KVV and KVVP is a hard line composed of a single strand of thick copper wire, ie, a BV wire.

The difference between AVVR and RVVP is that it is the same, except that the internal section is less than 0.75 square millimeters and the name is AVVR, and the name greater than or equal to 0.75 square millimeter is RVVP.

The quality of the cable in the security monitoring project is used to identify the quality of the cable. The real test requires specialized equipment and instruments. These equipment and instruments are not available in design and engineering units. In engineering practice, how to identify the video line is good or bad:

First, visual appearance identification:

1. PVC jacket: The surface can see that there is a regular "unevenness" in the inside of the net. This shows that the process is good and does not produce relative sliding. 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: Is the number enough? Copper wire mesh, check the weldability, tinned copper wire scraping to see if it is copper wire, the hardness of aluminum-magnesium alloy wire is obviously larger than copper wire; the weaving wire is sparse, the distribution is uneven, and the insulation layer is not tightly wrapped. cable;

3. Check the core: Diameter - SYV cable is 0.78-0.8mm, SYWV cable is 1.0mm; Recently there is a SYV75-5 cable diameter is 1.0mm cable, the characteristic impedance of this cable, certainly not 75 ohms, Not applied to 75 ohm transmission systems;

4. Check the binding force between the core and the insulating layer: Cut the insulating layer obliquely, and pull the core wire in the peeling direction to see if the core wire and the insulating layer are in contact with the process material; good cable has a large sealing force, and the poor cable does not have Stick together

5. Longitudinal Tensile Test: Take one meter cable, peel the cores, insulation, shields, and outer covers in layers and leave them 10 centimeters 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 cables" all have this problem;

Second, transmission performance test: video line, as the name suggests, is used to transmit video signal transmission line. Since it is a transmission video signal, at least we must understand the transmission characteristics of the transmission line in the 0-6M band range, or that the transmission performance. Here mainly to talk about "oscilloscope measurement method", a total of reference, because the oscilloscope is the necessary "weapons" for the project business, one of the mandatory inspection equipment qualification; the following statement is based on the ability to use the oscilloscope on the basis of proficiency.

1. Color camera video signal can be used as "standard video signal source": video camera output for test engineering, the amplitude should be 1 Vp-p on a 75 ohm load, that is, the peak level from the bottom of the line sync header to the highest white level of the video signal. - Peak value; note that the amplitude of the horizontal synchronization head is "-0.3V", 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 same cable Axial and characteristic impedance continuity.

3. Measure the DC resistance data of the cable: if the SYV75-5 cable is 1000 meters, the DC resistance core wire is 35-40 ohms, and the outer shield resistance is 1000 meters, it is 24-36 ohms (the shielding layer is different in number, the resistance is very different); 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 for engineering wiring, The quality of the pipe is inspected. If the pipe is broken when the pipe is worn, the resistance value becomes large, the video signal becomes weaker, and the interference should not appear. This kind of “accident” has a very high probability, but often Be ignored

4. Measure the high and low frequency attenuation characteristics of the cable: At the end, measure the head of the line and the amplitude of the burst head. Calculate the attenuation by taking 0.3V as the 0db reference. The same head represents the low-frequency attenuation, and the color burst represents 4.43M high-frequency attenuation. — — Such as: measured 1000 meters line synchronization head is 0.15V, according to the 20log calculation attenuation multiple db number is "-6db/1000m", measured 4.43M color synchronization head 1000 meters after attenuation is 30mv, that is 1/10 The attenuation is -20db/1000m. With this method, you can accurately grasp the transmission quality of different cables, and have an intuitive concept of "frequency distortion (high-low-frequency attenuation difference)". You can accurately measure the same model. The differences and performances of the SYV and SYWV cables of the structure are good or bad, and the differences and performances of the products of different manufacturers are compared. It is also possible to compare the changes of different batches of products from the same manufacturer.

5. The above method can also detect the performance of the video transmission system and equipment, such as the transmission characteristics of each coaxial video cable in the project, the transmission characteristics of the optical transceiver (can be measured as good or bad, do not think it is ideal), radio frequency transmission, microwave transmission characteristics , Twisted-pair transmission characteristics, distribution characteristics of video distributors, switching characteristics of the matrix host, we must pay special attention to when the multi-output switch the same input signal at the same time, if you find that the greater the number of switch-way attenuation, the wrong , It should be unchanged. After testing, you will master a lot of unqualified products. 6. Observe the field signal to see if the field synchronization position is greatly distorted (flat) - it should be flat; at the same time, you can also use an oscilloscope to observe the low-frequency interference situation: if the field signal has slow fluctuations, it is a 50/100-period interference. Many "thatch" beating, most of which are harmonics of frequency conversion, disconnect the remote camera and short-circuit the inner and outer conductors of the far end of the cable. At the end, the oscilloscope can directly observe the interference waveform and intensity; this method can also check and test the anti-jamming equipment. Real performance.