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Tang Daibing:
Guangdong wisdom security expert library expert
Qualified Internal Auditor of Enterprise Intellectual Property Management System
Chief technical expert of joint research and development of Wuhan University of Engineering
Participated in the declaration of various science and technology projects in Guangdong Province and Guangzhou City
Hubei Province Enterprise Intellectual Property Management System Demonstration Enterprise Reporter
Participated in the declaration of “High-tech Enterprise Certification†in Guangdong Province and Hubei Province and was approved
Participated in the "White Paper on Application Technology of Indoor Intelligent Wiring System in Buildings" of the Ministry of Housing and Urban-Rural Development
Participated in the technical preparation of many standards such as the GA/T1297-2016 "Security Cable" standard of the Ministry of Public Security
Quality Management System and Environmental Management System Certificate
Wire and cable product testing advanced skills professional qualification certificate
20 authorized utility model patent inventors
7 invention patent applicants
Person in charge of qualified quality of wire and cable "production license"
Foreword
On January 6, 2015, the expert review meeting of the Ministry of Public Security's "Technical Requirements for Cables for Safety and Security Systems" undertaken by Guangzhou Yuhong Wire & Cable Industry Co., Ltd. was held in Conghua, Guangzhou. The meeting invited the leaders of the Ministry of Public Security and the industry. The association and the major system integrators technical experts attended the meeting. The experts at the review meeting reviewed the standard clauses one by one and raised the discussion points. The leaders and experts of the conference fully affirmed the preparation of the standards and finally passed the review. The standard has been submitted. The superior unit applies for approval. Since August 2012, Guangzhou Yuhong Company has participated in the formulation of the “Technical Requirements for Cables for Safety and Security Systemsâ€. As an outstanding representative of domestic security cable companies, the company participated in the standard project, preparation, verification and research work. The company acts as South China. The only representative of the region, in the standard preparation process, combined with the security engineering and the major system integrators to fully communicate and discuss, put forward specific technical requirements and repeatedly verify. Guangzhou Yuhong's comprehensive security cable technology draft was approved and praised by the relevant leaders of the Ministry of Public Security, the Standards Committee, and the China Security Association.
At present, high-definition video surveillance systems are widely used in the security field. This system has extremely high requirements for cable structure stability and electrical transmission performance for video signal transmission. This is for cable manufacturers in product design, raw materials, production equipment, and testing equipment. Make higher demands. As one of the standard writing units, Guangzhou Yuhong Company puts high-standard video requirements on the technical parameters of the products, and uses its own advantages in production equipment and testing instruments to adopt a systematic method to produce high-definition video coaxial. Line product quality reliability for comprehensive production process control.
The high-definition video coaxial cable is divided into four layers from the inside to the outside: the center conductor, the insulator, the mesh conductive layer and the insulating outer sheath. The products of Guangzhou Yuhong Company are based on the RF Cable Design Guide GB/ The T11322.1-2008 specification requires processing. The company has a three-layer co-extrusion high-pressure nitrogen injection physical foam production line. The equipment has the functions of automatic adjustment of nitrogen pressure and on-line data monitoring and self-regulation of foaming degree. The production core has uniform foaming degree, stable characteristic impedance and attenuation of video signal transmission. small.
Product structure description:
1) Coaxial cable inner conductor:
In the national standard, the outer diameter of the copper conductor of this structure cable is 1.02 +/- 0.01 mm. Copper is the main material of the inner conductor. The inner conductor has a great influence on the signal transmission, because the attenuation is mainly caused by the resistance loss of the inner conductor. Its conductivity, especially surface conductivity, should be as high as possible. The quality of the copper material used for the inner conductor is very high. It is required that the copper material should be free from impurities and the surface is clean, smooth and smooth. The inner conductor diameter should be stable. Larger fluctuations in diameter will reduce impedance uniformity and return loss, so the outer diameter of the inner conductor should be precisely controlled.
In the actual production process, Guangzhou Yuhong's physical foam production line has the function of constant tension adjustment system. The system adjusts the tension of the pay-off and keeps the traction speed stable. The wire straightening device is used to solve the problem of non-uniformity and microbending of the copper wire, and the return loss value of the coaxial cable can be improved.
2) Coaxial cable insulation:
Coaxial cable media is much more than just insulation. The final transmission performance is determined primarily after insulation. Therefore, the choice of dielectric material and its structure are very important. All important properties, such as attenuation, impedance, and return loss, are strongly related to insulation. The most important requirements for insulation are low relative dielectric constant and small dielectric loss angle factor to ensure small attenuation, uniform characteristic impedance, large return loss and stable mechanical properties. The performance of the coaxial cable depends on the structure and quality of the single wire. The endothelial layer should be as thin and uniform as possible, and the concentricity is high. To reduce the attenuation, the thickness of the endothelial layer should be controlled at about 0.05 mm. The production equipment of Guangzhou Yuhong Company is a high-pressure nitrogen injection physical foaming method. Its control interface can automatically adjust the capacitance value in the water according to the set parameter value, characteristic impedance value, insulation outer diameter, same core degree, foaming degree, and its physics. The foaming degree can reach up to 80%, the physical foaming structure is consistent, the single-line characteristic impedance is uniform, and the return loss is large. The foam insulation layer is uniform and compact, each foam hole is sealed, the insulation is round and uniform, and the concentricity is over 95%. Insulation outer diameter tolerance ≤ ± 0.1mm; water capacitor online control tolerance ≤ ± 1.5pF / m. The characteristic impedance value is 75 +/- 3 Ω. The physical foaming insulation material is composed of HDPE, LDPE and nucleating agent in a certain proportion. It is produced by injecting nitrogen gas. The production line speed should be up to 120m/min, and the production line speed is fast, which can make up for the defects caused by uneven glue quantity and improve Return loss value.
The physical foaming production line can obtain a uniform and closed foam structure through the inner layer-foam layer-outer skin co-extrusion process, and has the characteristics of stable mechanical properties, high strength and good moisture resistance. A thin solid core PE is applied by injection on the outer surface of the foamed insulating layer. The outer skin layer can effectively prevent moisture intrusion, protect the performance of the coaxial cable from the beginning of production, and the insulating layer is tightly wrapped on the inner conductor through the inner layer, thereby further improving the mechanical stability of the cable. The stability of the traction of the equipment is one of the key factors for the production of physical foaming single wire. The front and rear double traction are used, and the front and rear traction are active two-wheel horizontal tractors. The wheel diameter is 1000mm, which is composed of frequency conversion speed regulation device and constant tension adjustment system to ensure stable traction and synchronization. 1000mm horizontal active traction, due to the large wheel diameter, the traction speed should be up to 120m/min. It can increase the traction stability, reduce the microbend of the copper wire and increase the return loss value.
3) Coaxial cable outer conductor:
The outer conductor has two basic functions: the first is the function of the return conductor, the second is the shielding effect, the shield woven mesh is combined with the aluminum foil longitudinally, which is effective against electromagnetic interference, and the aluminum foil is a 50 mm thick hot-melt structure. The braided layer is tinned copper with an outer diameter of 0.12mm-0.18mm. During the weaving process, the aluminum base thickness of the aluminum foil, the longitudinal lap width, the number of meshes, the number of ingots, the angle of the clip, and the shielding rate all affect the shielding. The attenuation performance parameters are verified by the cable specifications in actual production.
4) Coaxial cable outer sheath:
The outer sheath material of the coaxial cable is composed of polyvinyl chloride. The average thickness of the sheath is 0.88mm, and the outer diameter is 7.2mm. The weather resistance and mechanical properties are in accordance with: high temperature test 80±2°C, 168 hours, low temperature experiment. -25±3°C, 20 hours, no mechanical loss of outer sheath and insulation layer, damp heat test 40±2°C, 90%-95%, 96 hours, insulation resistance meets the specified value, attenuation value increment ≤5%, The sheath and outer conductor cannot be cracked.
Performance requirements:
The high-definition video coaxial cable electrical transmission performance meets the following requirements:
HD video coaxial cable integrated data
Product performance control method:
1) Characteristic impedance
The main parameter to consider for HD video coaxial cable is the characteristic impedance. The transmission line matching condition is that the line terminal load impedance is exactly equal to the characteristic impedance of the transmission line. At this time, there is no energy reflection, and thus the highest transmission efficiency. The relevant performance parameter test method refers to the requirements of Section 5.2.5 of the GY/T135-1998 standard. It can be confirmed by test analysis by laboratory TDR instrument. The characteristic impedance depends on the structural size of the cable and the dielectric constant of the insulating material, and the physical foamed insulating material has a lower dielectric constant. The degree of foaming, the outer diameter of the insulation and the characteristic impedance are proportional, increasing the degree of foaming, increasing the outer diameter of the insulation, and increasing the characteristic impedance, and vice versa. The degree of foaming is inversely proportional to the capacitance value in the water. The characteristic impedance is inversely proportional to the capacitance value in the water. That is, the larger the characteristic impedance value, the smaller the capacitance value in the water. The capacitance value in water is proportional to the dielectric constant. The larger the capacitance value in water, the larger the dielectric constant, and vice versa. When the physical foaming line equipment interface shows that the characteristic impedance value is outside the standard range, the extruder screw speed or the traction wheel speed can be adjusted by adjusting the foaming degree or the outer diameter of the insulation, that is, within the allowable range of the insulation outer diameter tolerance. Make the capacitance value of the wire in the water meet the requirements; if the capacitance value in the wire water is too small, within the range allowed by the outer diameter tolerance, slow down the screw speed of the extruder main engine or adjust the rotation speed of the pulley to make the capacitance in the core water reach Claim. When the outer diameter of the wire cannot be adjusted to meet the target requirement, the insulation property of the insulating material may be problematic. The degree of foaming of the wire may be changed by adjusting the temperature of the cooling water or moving the cold water tank. Adjusting the temperature of the extruder head can change the degree of foaming and change the insulation performance of the material. However, because the temperature of the extruder head is very sensitive to the degree of foaming, try not to adjust the degree of foaming by adjusting the head, and change the machine. Head temperature also affects changes in other process parameters. When the above-mentioned outer diameter adjustment and foaming degree adjustment are not able to achieve the target capacitance requirement of the wire, the structure of the wire is likely to have problems. It is necessary to check whether the core wire is eccentric, the wire is released, and the tension of the wire is too large to cause copper. The wire is drawn down to adjust the extrusion process conditions to the optimum state
2) Attenuation constant
The attenuation constant reflects the amount of loss of electromagnetic wave energy as it travels along the cable, and typically requires the cable to have as low an attenuation constant as possible. The attenuation is composed of the sum of the loss of the inner and outer conductors and the dielectric loss of the insulating material supporting the conductor, wherein the conductor loss is dominant, especially the inner conductor has the largest attenuation, which accounts for about 80% of the attenuation of the entire conductor. The low frequency end is mainly the conductor attenuation, such as the outer diameter of the conductor is small, the conductor is scratched, oxidized, and the adhesion is poor. As the frequency increases, the dielectric attenuation increases. The attenuation of the coaxial cable is related to the conductor, medium, structural size, process level and operating frequency. The attenuation constant below 50MHz does not match the nominal value, while the high frequency has a margin, often the aluminum base in the aluminum foil is too thin. Therefore, when the frequency is relatively low, the thickness of the aluminum base is less than or equal to the transmission depth of the frequency, resulting in an excessive attenuation value. According to theoretical calculations, the transmission depth of the aluminum layer at a frequency of 50 MHz is 12.2 μm, and generally taking an aluminum base of 38 μm or more can solve this problem. The physical foaming PE has a good attenuation at low frequencies, while the high frequency (such as over 800 MHz) is out of tolerance, mostly related to the large dielectric constant, that is, the capacitance value in the water is too large. Or it is related to the excessively small braiding density of the outer conductor and the small outer diameter of the inner conductor. In addition, the attenuation constant also depends on the degree of foaming. Appropriately increase the degree of foaming in the range allowed by the impedance and echo (can increase the degree of foaming, increase the impedance, and reduce the attenuation.) It can help to improve the attenuation constant of the cable, and also reduce the cost. The relevant performance parameter method can be referred to. The requirements of Section 5.2.6 of the GY/T135-1998 standard are confirmed by the laboratory network analyzer.
3) Return loss
The return loss is due to signal reflection caused by the characteristic impedance non-uniformity of the coaxial cable. Return loss affects the amplitude of the signal received by the receiver, which reduces the effective transmission distance of the cable. The relevant performance parameter test can be carried out by referring to the requirements of the RF cable impedance uniformity measurement method (GB/T12792-1991), and the test analysis and confirmation by the laboratory TDR instrument. Good return loss performance is the key to ensuring high frequency and high rate transmission performance. In the inner conductor produced during the production of coaxial cable, the dimensional deviation of the insulator structure and the deformation of the material may cause local unevenness of the characteristic impedance of the cable. When the cable is added with a transmission signal, the reflection of the signal may be facilitated. The larger the return loss value is, the smaller the signal reflection coefficient is, the better the internal homogeneity of the cable is. In the actual production process, the fluctuation of the conductor and the outer diameter of the insulation can be strictly controlled to ensure that the insulation has the same core degree of 95% or more. Conductors and insulators are free of oxidative scratches.
4) Shield attenuation
A system with poor shielding performance will destroy the normal transmission of the affected signal and reduce the transmission quality of the system. The shielding performance of HD video coaxial cable can be reflected by the shielding factor, shielding attenuation and transfer impedance. The larger the shielding attenuation, the smaller the shielding coefficient, indicating that the cable shielding performance is better. In the actual weaving production process, the aluminum foil overlap width should be no less than 5mm, the thickness of the aluminum layer is increased to 38μm or more, and the relationship between attenuation, echo, and shielding can be reasonably arranged, and the degree of foaming can be reasonably reduced under the condition of acceptable attenuation, and the shielding can be improved. Both the effect and the echo are favorable. The quality of the aluminum foil is good, especially the flexibility, and it is bent without any cracks. The wire insulation shielding design should consider the following factors: the thickness of the aluminum base and the number of layers of the aluminum surface have a certain correlation with the shielding attenuation. The hot-melt aluminum foil of the same specification is basically 3-5dB better than the single-sided aluminum foil of the same specification. The same structure of the wire, the same weaving density, the conductor with a small outer diameter of the braided filament has better shielding effect than the large conductor. Within about 90 dB, the density of the braid is basically related to the damping capacity of the shield, that is, the greater the weaving density, The stronger the shielding attenuation, the shielding attenuation can reach 80 dB when the shielding rate is 65%. For the relevant performance parameter test, refer to the cable clamp system RF coaxial cable shielding performance technical requirements and test methods (GY/T186-2002). The 5.1 section of the standard requires the absorption clamp method. In addition, the HD video coaxial cable shielding attenuation test method can be divided. In order to describe it indirectly by measuring the surface transfer impedance of the coaxial cable, the triax method is a typical transfer impedance measurement method. In many cases, especially when the frequency is low (below 10 MHz), the transfer impedance can be used indirectly. Describe the shield attenuation of the shielded cable. The lower the transfer impedance, the better the shielding performance of the shielded cable.
Production quality assurance is due to the attention to the details of the production process, especially the reliability of the material and the effectiveness of the structural dimensions, the stability of the equipment, the effectiveness of the implementation of the process parameters are the focus of our process inspection, only these details Monitoring confirms that the process is effective and we can produce qualified products.