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Construction of EMC Semi-Radio Anechoic Chamber

Author:admin   AddTime:2021-03-19

Electromagnetic compatibility (EMC) refers to the ability of a device or system to operate in compliance with the requirements in its electromagnetic environment and not produce intolerable electromagnetic interference to any device in its environment. Therefore, EMC includes two requirements: on the one hand, the electromagnetic interference generated by the equipment in the environment during normal operation cannot exceed a certain limit; on the other hand, it means that the equipment has a certain degree of electromagnetic interference in the environment. The degree of immunity, that is, electromagnetic susceptibility. Electromagnetic compatibility (EMC) is divided into electromagnetic interference (EMI) and electromagnetic tolerance (EMS). All electronic products must comply with the general provisions of electromagnetic compatibility. Electromagnetic compatibility issues are constantly being used in various products such as electronics, electrical machinery, information, and communications to introduce new technologies. In addition to users' requirements for communication quality, electromagnetic compatibility is also under the active development of relevant regulations and control by governments of various countries. The importance and urgency of related issues. For example, Europe has strengthened the implementation of post-market testing of imported products, which has caused many barriers to occur.

The National Bus Quality Supervision and Inspection Center introduced an electromagnetic compatibility laboratory from Germany including 3/5 m semi-anechoic chamber, conduction test shielding room, shielding amplifier room, etc., which was completed in February 2005 and passed the Chinese laboratory successfully. Acceptance by the National Accreditation Service (CNAL). During the planning and construction of the 3/ 5 m semi-anechoic chamber in the center, we have accumulated and summed up a part of the experience for your reference and reference.

1 Selection and construction of the overall scheme of the semi-anechoic chamber
The electromagnetic compatible semi-anechoic chamber is mainly used to replace the open test field without electromagnetic interference for electromagnetic radiation disturbance measurement and electromagnetic radiation sensitivity measurement. Since the test environment of the semi-anechoic chamber needs to simulate the electromagnetic wave propagation conditions of the open test site (that is, there are only direct waves and ground reflected waves when electromagnetic waves propagate), the size of the anechoic chamber should be based on the structural requirements of the open test field, which is generally divided into standard 10 m method, 5 m method and 3 m method, etc. There are many types of semi-anechoic chambers, and there are big differences in function, structure, material selection, and installation form.

But which scheme is adopted depends mainly on the type of test required by the user, the space size of the object to be tested, and the test level. First of all, we must clarify the test frequency range, whether it is for military standard testing or civil standard testing, whether to conduct internal pre-compatibility and diagnostic testing by the manufacturer, or to conduct third-party certification testing; secondly, it is necessary to clarify the maximum space and test that the tested object may occupy. The laboratory's main application standards, its own financial status, and possible future expansion and upgrade requirements and other factors, select a suitable and feasible test site and equipment configuration plan.

There are two basic ways to construct a semi-anechoic chamber: assembled and welded. The assembled shell is composed of a formed steel plate (made by two bending plates on four sides) and a bolt-fixed module. There are conductive gaskets between any two adjacent shielding modules to ensure excellent radio frequency shielding and electrical continuity. This method has a light structure, is easy to assemble, is convenient for future maintenance and disassembly, and has a short construction period. The welding shielding system consists of large pieces of steel plates welded together, which form a tight radio frequency seal. The advantage of soldering package is that it is durable, and has higher shielding performance due to the elimination of joint leakage, but it is not easy to disassemble and is suitable for fixed places.

Due to the different types of shielding plates used by various darkroom manufacturers to build darkrooms, the connection methods and processes between the shielding plates are also different. In order to ensure good electrical contact and sealing, the shielding plates and their connection methods used by them should be understood and compared in detail. , And choose according to the actual construction period and other requirements.

2 Parent building and infrastructure
Building an EMC laboratory is a systematic project, which follows the scientific design interface relationship: test equipment → semi-anechoic chamber → parent building design. For the implementation of specific projects, the sequence is just the opposite, going through the process of parent building construction → semi-anechoic chamber installation → test equipment installation and commissioning. Therefore, the parent building must be built before the semi-anechoic chamber is constructed, including floor space, structural bearing capacity, space size, power supply, air supply, air conditioning, and waterproofing. The design of the parent building must first consider sufficient ceiling height to accommodate the semi-anechoic chamber, conduction test shielded room, shielded amplifier room, and other ancillary facilities.

Sufficient space must be reserved between the parent building and the dark room to facilitate the installation, maintenance and ventilation of the dark room. The floor of the parent building mainly bears the weight and load of all shields and installation parts, and special attention is also required. The ground for civil construction needs to be laid carefully, the waviness of the ground should not exceed a few millimeters within a few meters, and there is a high requirement for moisture resistance. In addition, the turntable in the dark room needs to be installed in a concrete pit of a certain depth, the terrain is low, and it must be waterproofed.

Before installing the darkroom, there is generally a relatively high residual humidity requirement for the bearing ground, and a grounding point with a very low grounding resistance must be provided for each test room. Since there are many interface problems between the darkroom and the parent building, and domestic construction companies basically have no experience to learn from some of these requirements, it is very important to let the civil design unit, construction unit and darkroom manufacturer communicate and communicate as much as possible. necessary.

3 Several aspects involved in semi-anechoic chamber construction
1. The size of the anechoic chamber. You should know whether the anechoic chamber you want to build is a standard 10-meter semi-anechoic chamber or a standard 3-meter semi-anechoic chamber, or an anechoic chamber with a customized size according to your site requirements; whether the anechoic chamber should be equipped with a shielded control room and amplifier room , What are their respective length, width, and height dimensions, and in which direction they are built in the darkroom.

2. Type, size and quantity of screen doors. There are different types of screen doors, such as single pole, double pole, and three pole, and there are three kinds of electric, pneumatic and manual. You should choose them based on your future equipment under test and the ease of access for personnel, as well as the shielding performance, durability, reliability, and ease of maintenance of the screen door.

3. The type and connection method of the shielding plate. Due to the different types of shielding plates used by various darkroom manufacturers to build the darkrooms, the connection methods and processes between the shielding plates are also different. In order to ensure good contact tightness and electrical continuity, attention should be paid to their selection of shielding plates and the connection methods between the shielding plates to understand and compare.

4. Shielding performance of shielded room. Darkroom manufacturers should be asked to provide specific shielding performance indicators (given specific values) that their electromagnetic shielding rooms can achieve, which should include the shielding performance of different frequency ranges (from low frequency to high frequency) against magnetic fields, electric fields, plane waves, and microwaves index.

5. Absorbing materials. Pay attention to the manufacturers and models of the absorbing materials used by the darkroom manufacturers (including ferrite absorbing materials and wedge absorbing materials); pay attention to the composition and structure of the absorbing material and its resistance to high temperature, high humidity and flame retardancy Performance; understand whether it is easy to deform in long-term use and the absorbing performance of various absorbing materials in different frequency bands, and understand their laying methods, laying positions and functions in the darkroom.

6. Power line and signal line filter. Consider the types of power supplies to be used in the darkroom and their maximum power in the future, such as whether the test equipment, test equipment, auxiliary equipment, and lighting system should use 380V, 220V, 110V AC voltage, and whether there is a need for DC power supply for testing and testing Equipment, their quantity, whether there are special test equipment and auxiliary equipment that require special filters, etc. All these need to be considered so that the supplier can prepare these power line and signal line filters in advance.

7. Signal guide plate and waveguide ventilation window. In the dark room, it is necessary to install waveguide ventilation windows to connect with exhaust fans or air conditioning systems. Pay attention to the frequency band design of the waveguide ventilation window, and its shielding performance must meet the shielding performance of the shielded room. The signal guide board is used to install terminals or signal interfaces that cannot be installed directly through the shielding wall; the number and location of the signal guide board and the number and type of terminals on it should be determined through consultation with the test equipment supplier.

8. Fire alarm devices and lighting facilities. Pay attention to the selection of lighting facilities that will not produce any radio interference; the installation of the fire alarm device should not affect the performance of the dark room.

9. The automation device in the dark room. The automation equipment in the darkroom includes the antenna tower, the turntable, the monitoring system and the controller that can control them. The choice of antenna tower should consider the manufacturer, model and whether there is an adapter to install the antenna, whether it is supported by the test equipment (that is, whether the test software of the test equipment connected to it has a driver that supports it); the turntable should also be affected The test equipment is supported and the size and carrying capacity of the turntable are determined according to the size of the equipment under test. At the same time, the rotation angle and positioning accuracy of the turntable should be considered; the monitoring system includes a camera installed in the dark room and a monitor placed in the control room. Choose the number of cameras and monitors according to the actual use. The camera should be selected that can work normally in a wide frequency range and high field strength and will not produce radio frequency interference signals, and install it in a non-rural Shot area.

10. Performance testing and warranty training in the darkroom. Because the darkroom is not only suitable for EMI testing in EMC, but also for radiated immunity testing in EMS. Therefore, the performance test of the darkroom should include the shielding performance test after the darkroom shield is built, and the field attenuation test and field uniformity test after the darkroom is fully constructed. These tests should be carried out in accordance with the contract requirements and the relevant international standards for the acceptance of darkroom construction. It is necessary to choose a well-known and authorized testing organization. The warranty of the darkroom and the warranty of the supporting equipment, parts and training shall be written into the contract.

4 Features and functions of this electromagnetic compatibility laboratory
The electromagnetic compatibility laboratory of the National Passenger Car Quality Supervision and Inspection Center is mainly composed of four parts: a semi-anechoic chamber, a conduction test shielding room, a shielding amplifier room and a shielding control room. The size of the shielding body of the darkroom is 17.6 m in length, 13.5 m in width and 9.5 m in height. The darkroom is equipped with a turntable with a load-bearing 8,000 kg and a diameter of 5 m and an automatic lift of 0.8 to 4 m. Antenna system and exhaust exhaust system. The working frequency of the darkroom is 9 kHz~40 GHz, and the quiet area of the test area above the turntable in the darkroom is a cylinder with a height of <4 m and a height of 2 m. The inside of the dark room is also equipped with a pneumatic fixing device and a cooling fan. It can complete the radiation and conduction emission test, radiation and conduction immunity test of the entire automobile and its electronic parts, motorcycle and its electronic parts, as well as the electrostatic discharge test of the entire vehicle.

The size of the conduction test shielding room is 8.0 m in length, 4.0 m in width, and 3.0 m in height. In addition to completing the tests of the conduction transient emission, conduction immunity, electrostatic discharge and other items of automotive parts, it also It can complete the test of conducted disturbance voltage, absorbed power, disturbance magnetic field and other items of household appliances, power tools, electrical lighting equipment, etc.

All the items in the laboratory have passed the third-party test from abroad, and all the indicators are much better than the requirements of relevant international standards. The configuration and performance of the laboratory have reached the international advanced level, providing an ideal test environment for the EMC performance of a variety of electromechanical products, mainly automobiles, motorcycles and their parts.

Absorbing Material:https://www.goodsmaterial.com/

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