The choice of EMC test system will have a direct impact on test standards and automotive laboratory testing capabilities

With the increasingly complex electromagnetic environment in the living space and the widespread application of electronic technology in automobiles, all automobiles will be exposed to a large number of external electromagnetic interference and self interference environments. The issue of electromagnetic compatibility (EMC) of automobiles will become increasingly prominent, and the corresponding test methods must also be improved.

1. The necessity of building an automotive EMC laboratory

The rapid development of the automotive industry and the fierce competition in the automotive market have greatly promoted the widespread application of various electrical, electronic, information, and electronic equipment in the automotive industry. At present, electronic devices have been widely used Widely used in automotive engine control systems, automatic transmission systems, braking systems, and in regulating and driving systems, the safety, reliability, and comfort of vehicles play a crucial role. However, with the increase in the number and type of automotive electronic devices, and the increase in their operating frequency, the electromagnetic environment of automobiles becomes increasingly complex. At the same time, electronic devices and devices in automobiles, especially semiconductor logic devices, are very sensitive to electromagnetic interference, and electronic devices in automobiles often interfere with each other. Even so, the widespread application of automotive electrical equipment is still increasing, and its internal electromagnetic environment will become even worse, and mutual electromagnetic compatibility interference will become more serious.

Any foreign electronic product must undergo performance testing and performance testing EMC testing before being applied to automobiles; Before commercialization, it must undergo rigorous matching tests and the most critical matching test EMC certification. For electronic products that have not been strictly tested, no vehicle will be used, which is also the key to the difficulty of domestic enterprise products entering the foreign automotive parts supply chain. EMC involves the safety and reliability of complete vehicles, and foreign automotive companies will not easily use components and products that have not undergone reliability testing.

2. EMC Lab Construction Plan

The automotive EMC laboratory is divided into component level and vehicle level. In addition to adding vehicle hub systems to the vehicle level laboratory, there are only scale differences. These two laboratories include a test environment and a test system, namely a semi anechoic chamber, or anechoic chamber, required for automotive EMC testing. The test system is divided into a semi anechoic chamber. EMI test system and EMS test system, namely, electromagnetic interference test and electromagnetic immunity test.

2.1 EMC Test Environment Planning

The half of the test environment is generally composed of an anechoic chamber, while the control room and power amplifier are composed of power amplifiers. An anechoic chamber is a shielding chamber with an internal layer of absorbing material. The function of the shielding room is to prevent outdoor electromagnetic waves from entering the laboratory and prevent electromagnetic waves from transmitting outside the laboratory; The function of the absorbing material is to absorb the electromagnetic waves emitted by the tested components in the laboratory to avoid errors in the test results caused by reflection; The control room is used to place fully compatible receivers, signal generators, monitoring computers, and other equipment for monitoring the test process and results; The power amplifier is placed in the power amplifier room. The power amplifier itself has strong radiation and is harmful to people, so it is placed separately.

Figure 1 is a schematic diagram of a 3-meter method laboratory:

Figure Sketch map of the 3m method laboratory

The anechoic chamber itself is a simulated open space without electromagnetic interference, so the anechoic chamber itself is a simulated open space without electromagnetic interference. EMC laboratories are recommended to be built in a relatively quiet, vibration free, and strong electromagnetic environment. At the same time, EMC laboratories designed specifically for automotive components or vehicles must consider smoke exhaust. For automotive components. EMC Lab recommends leaving more waveguides on the wall of the darkroom to provide photoelectric transmission channels or facilitate the introduction of compressed air pipes, which will play an important role in future experiments.

It is recommended to install telephone filters and signal filters in the control room, as the control room is also a shielded room, which can solve the problem of communication with the outside world.

2.2 EMC test system planning

The selection of EMC testing systems will directly affect testing standards and laboratory testing capabilities, so targeted research and selection is particularly important. EMC standards include relevant standards formulated by international standards, regions, automotive industry associations, and other standardization organizations. Since the 1960s, EMC has experienced approximately 50 years of development in this standard. The standards of various standards organizations basically include vehicle and component testing standards, and each standard corresponds to and refers to each other, that is, in addition to the severity of the standards, test content and test methods converge.

CISPR and ISO standards cover all automotive categories, and EMC testing content also provides a model and foundation for other regional organizations and enterprise standards.

The automotive EMC standards developed by ISO and CISPR include the following Table 1:

In addition to differences in the rigor of standards, test content and methods have also converged, which also provides opportunities for companies or institutions that are relatively short of funds to gradually build. At this point, we need to consider in detail which equipment must be in place at once and which equipment can be gradually improved. For the test system we are discussing, if we plan to implement it gradually, we can consider making overall planning from the test project or test intensity. For example, we can list transient interference and anti-interference devices independent of the anechoic chamber, electrostatic discharge devices, and expensive power amplifiers.

3. Matters needing attention during the construction of EMC laboratory

Since the implementation of a project generally separates the environment from the system, issues that should be noted during the respective construction or selection process are also discussed separately.

3.1 During EMC construction, attention should be paid to the test environment (semi anechoic chamber)

The following requirements must be met before construction of a semi anechoic chamber:

(1) The 3m method darkroom L * W * H is about 9m * 6m * 6m, and the 10m method darkroom L * W * H is about 21m * 13m * 9m. The laboratory requires no beams or columns separated by buildings or structures;

(2) The flatness of any 3m ground shall not exceed 3mm, and no accumulated error is allowed. Within the installation range of the darkroom, there should be no accumulated error in the ground flatness, resulting in the ground tilting, as the splicing shield plate is the standard size of the factory finished product. If the ground is uneven, it is difficult to assemble, affecting the shielding effect;

(3) Before connecting to the filter, there is no leakage protection device or isolation transformer in the power supply system; The power system capacity supply meets the testing and darkroom power distribution requirements, taking into account the power consumption mode and capacity of the object under test;

(4) Whether it is a vehicle or component testing laboratory, it is necessary to consider the method of entering the laboratory for the entire vehicle or component, that is, planning the form of shielded doors;

(5) Provide an independent grounding system for the darkroom, with ground resistance less than 0.5 ohms;

(6) The bearing capacity of the foundation and laboratory ground should be considered to meet the bearing requirements of test equipment, vehicles, or components.

The following issues must be considered during darkroom construction:

(1) The surrounding and top of the laboratory are waterproof, as the shielding mat filled at the direct joint of the shielding material may rust, resulting in poor shielding effectiveness;

(2) The installation method of the wave absorbing wedge must be confirmed. Improper installation methods can cause unreliable installation or contaminate the test environment;

(3) The ferrite backing board needs to be environmentally friendly wood board, because the laboratory environment is closed, and non environmentally friendly materials can directly cause environmental pollution in the test;

(4) The doors of the darkroom and amplifier room should be associated with the test system to ensure the safety of the test personnel.

(5) The interface board of each shielded room should choose a conservative interface form as much as possible, because the shielding efficiency of the interface board is prone to problems;

3.22 Precautions for testing systems

If you choose the right vendor, EMC generally has no problems testing the system. The only thing to note is that the key instruments and equipment for the test system are imported from abroad. According to domestic regulations, imported equipment can only be used after being remeasured by domestic measurement institutions, so this part of the cost should be specified before procurement.

4. Conclusion

The construction of EMC laboratory is a relatively complex system engineering, and the aspects to be considered are not limited to the content described in this article. The content described in this article is for the use of the author's experience in the construction of EMC laboratories only. EMC laboratories are only discussing opinions and suggestions from the perspective of vehicle planning and construction.