True detection of video lines also requires specialized equipment and instruments. These equipment and instruments are not available in design and engineering units. The project distinguishes the quality of the video line and hopes that everyone will brainstorm. Let's talk about a few points here.
(a). Visually Appearance Appraisal:
1. PVC sheath: The cable is made of high-quality PVC that is resistant to high temperature 70°C and low temperature minus 20°. The surface is smooth, smooth, clean, black in color, and has good tensile strength. It should be able to see from the surface of the cable. There is a regular "unevenness" in the crimping of the inside of the net, which means that the extrusion process of Zhenya cable is good and does not produce relative slipping. It is a good cable. The ordinary cable, rough surface, uneven color, not only shows that the plastic material, processing technology and poor plasticization performance, at the same time, if the plastic surface of large air holes, it is easy to damp and affect product performance and service life. Pulling easily with a hand pull may be an inferior quality material. 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: The outer shield of the cable SYV75-5 is divided into 96 series, the SYV75-5 is encrypted 128 series, the outer shield of the Zhenya cable SYV75-3 is 96 series, and the material is oxygen-free copper, and the shielding net is uniformly knitted. , The welding performance is very good, and the tinned copper wire scrapes inside to see if it is a copper wire. And other manufacturers of cables you must first check the material, is not pure copper, is not a black rod copper, there are many manufacturers shielded mesh using copper clad aluminum, aluminum-magnesium alloy wire hardness is significantly greater than the copper wire; braided network is sparse, distribution is not Uniform, and the insulation layer is not tight, such as poor cable;
3. Check the core wire: The outside diameter of the SYV75-3 insulation is 3.00+0.13mm, and the outside diameter of the SYV75-5 is 4.80+0.20mm. Recently, a cable with an ODV75-5 insulation outside diameter of 4.0mm has appeared. The characteristic impedance of this type of cable is definitely not 75 ohms and it is not applied to a 75 ohm transmission system;
4. Check the binding force between the core and the insulating layer: diagonally cut the insulation layer of the video cable, 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; Joint force, poor cable does not bond;
5. Longitudinal tensile test: Take one meter screen cable, peel off the core layer, insulation layer, shield 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 cables" all have this problem;
(II). Transmission performance test:
Video cable, as the name implies, is a transmission line used to transmit video signals. Since it is a transmission video signal, it is at least necessary to understand the transmission characteristics of the transmission line in the 0-6M band, or 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, 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. The color camera video signal can be used as a “standard video sourceâ€: the video output of the camera used for the test project should have a magnitude of 1 Vp-p on a 75 ohm load, that is, the bottom of the horizontal synchronization head to the highest white level of the video signal. "Peak-Peak"; 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 state. 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 methods, because the welding method destroys the cable Continuity of coaxiality and characteristic impedance.
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 (different shield layers and different resistances) 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 materials, 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 the burst head at the end. Calculate the attenuation with 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 1000m line sync head is 0.15V, according to 20log attenuated multiple db number is "-6db/1000m", measured 4.43M color sync head 1000m attenuation amplitude is 30mv, that is 1 /10 times, 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 more accurately measure The difference and performance of SYV and SYWV cables of the same type and structure are good and bad, and the differences and performances of different manufacturers' products 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 so ideal), radio frequency transmission, microwave Transmission characteristics, transmission characteristics of twisted pair, distribution characteristics of video distributors, switching characteristics of the matrix master, special attention should be paid to the fact that when multiple outputs simultaneously switch the same input signal, the larger the number of switching paths, the greater the attenuation. It's not right. It should be unchanged. After testing, you will master a lot of unqualified products.
6. Observe the field signal to see if the position of the field synchronization distortion is not large (flat) - it should be very flat;
7. At the same time, you can also use the oscilloscope to view the low-frequency interference situation: If the field signal has slow fluctuations, it is 50/100-week interference, there are many "thatch" beats, mostly frequency harmonics interference, the remote camera disconnected, cable The distal inner and outer conductors are short-circuited. At the end, the oscilloscope can directly observe the interference waveform and intensity; this method can also check and test the real performance of the anti-jamming device;
(a). Visually Appearance Appraisal:
1. PVC sheath: The cable is made of high-quality PVC that is resistant to high temperature 70°C and low temperature minus 20°. The surface is smooth, smooth, clean, black in color, and has good tensile strength. It should be able to see from the surface of the cable. There is a regular "unevenness" in the crimping of the inside of the net, which means that the extrusion process of Zhenya cable is good and does not produce relative slipping. It is a good cable. The ordinary cable, rough surface, uneven color, not only shows that the plastic material, processing technology and poor plasticization performance, at the same time, if the plastic surface of large air holes, it is easy to damp and affect product performance and service life. Pulling easily with a hand pull may be an inferior quality material. 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: The outer shield of the cable SYV75-5 is divided into 96 series, the SYV75-5 is encrypted 128 series, the outer shield of the Zhenya cable SYV75-3 is 96 series, and the material is oxygen-free copper, and the shielding net is uniformly knitted. , The welding performance is very good, and the tinned copper wire scrapes inside to see if it is a copper wire. And other manufacturers of cables you must first check the material, is not pure copper, is not a black rod copper, there are many manufacturers shielded mesh using copper clad aluminum, aluminum-magnesium alloy wire hardness is significantly greater than the copper wire; braided network is sparse, distribution is not Uniform, and the insulation layer is not tight, such as poor cable;
3. Check the core wire: The outside diameter of the SYV75-3 insulation is 3.00+0.13mm, and the outside diameter of the SYV75-5 is 4.80+0.20mm. Recently, a cable with an ODV75-5 insulation outside diameter of 4.0mm has appeared. The characteristic impedance of this type of cable is definitely not 75 ohms and it is not applied to a 75 ohm transmission system;
4. Check the binding force between the core and the insulating layer: diagonally cut the insulation layer of the video cable, 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; Joint force, poor cable does not bond;
5. Longitudinal tensile test: Take one meter screen cable, peel off the core layer, insulation layer, shield 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 cables" all have this problem;
(II). Transmission performance test:
Video cable, as the name implies, is a transmission line used to transmit video signals. Since it is a transmission video signal, it is at least necessary to understand the transmission characteristics of the transmission line in the 0-6M band, or 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, 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. The color camera video signal can be used as a “standard video sourceâ€: the video output of the camera used for the test project should have a magnitude of 1 Vp-p on a 75 ohm load, that is, the bottom of the horizontal synchronization head to the highest white level of the video signal. "Peak-Peak"; 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 state. 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 methods, because the welding method destroys the cable Continuity of coaxiality and characteristic impedance.
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 (different shield layers and different resistances) 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 materials, 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 the burst head at the end. Calculate the attenuation with 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 1000m line sync head is 0.15V, according to 20log attenuated multiple db number is "-6db/1000m", measured 4.43M color sync head 1000m attenuation amplitude is 30mv, that is 1 /10 times, 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 more accurately measure The difference and performance of SYV and SYWV cables of the same type and structure are good and bad, and the differences and performances of different manufacturers' products 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 so ideal), radio frequency transmission, microwave Transmission characteristics, transmission characteristics of twisted pair, distribution characteristics of video distributors, switching characteristics of the matrix master, special attention should be paid to the fact that when multiple outputs simultaneously switch the same input signal, the larger the number of switching paths, the greater the attenuation. It's not right. It should be unchanged. After testing, you will master a lot of unqualified products.
6. Observe the field signal to see if the position of the field synchronization distortion is not large (flat) - it should be very flat;
7. At the same time, you can also use the oscilloscope to view the low-frequency interference situation: If the field signal has slow fluctuations, it is 50/100-week interference, there are many "thatch" beats, mostly frequency harmonics interference, the remote camera disconnected, cable The distal inner and outer conductors are short-circuited. At the end, the oscilloscope can directly observe the interference waveform and intensity; this method can also check and test the real performance of the anti-jamming device;
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