What are the EMC test items and configurations

1、 Definition:

The concept of EMC (electromagnetic compatibility) includes two aspects: first, the equipment shall be able to work normally under certain electromagnetic environment, that is, the equipment shall have certain electromagnetic immunity (EMS); Second, the electromagnetic interference of the equipment itself will not cause too much damage to other electronic equipment, that is, electromagnetic interference (EMI).

In order to standardize the electromagnetic compatibility of electronic products, countries around the world have established relevant EMC specifications for products. For example, Europe issued a mandatory certification EMC order on CE. The United States issued Part15B/CPart22/24CPart22/24 in FCC regulations. China CC issued compulsory certification GB9254. GB4943.1. This is a strong guarantee for the policy of electronic products EMC verification. Therefore, the goods should meet the requirements. According to the laws and regulations, the sales of goods in violation of EMC laws and regulations will face huge penalties. Therefore, manufacturers pay more and more attention to the electromagnetic compatibility of products.

EMC test projects mainly include two categories:

First, EMC laboratory: EMC laboratory refers to EMC test environmental factors. EMC test is a high-precision professional test. Environmental factors cannot have interference signals. EMC laboratory can shield external interference signals, which is the key guarantee of EMC test. EMC should consider several parameters of the laboratory, the first is the shielding efficiency, that is, the main parameters to check the external space radiation of the EMC laboratory shielding, the second is the grounding resistance. The grounding resistance of the CNAS must be less than 4 Ω. Assuming that the grounding resistance is too large, it will affect the background noise of the EMC test and endanger the analysis of the test results. The third is the external power supply. The EMC laboratory filter has leakage current, and many EUTs have non-traditional power supply voltage, so the power supply is particularly important. If the EMC characteristics of the power supply itself are not qualified, the background noise of the EMC test will directly affect the analysis of the test results.

Second, EMC test equipment: EMC test equipment is the core standard for completing the test report. Although EMC has many test equipment on the market that should consider more factors, such as EMC test manufacturers, overseas Rhodes and Schwartz. EMTest, etc., and domestic Hangzhou Space, etc., from the perspective of cost, China's equipment is far lower than imported products. From the perspective of after-sales service, although the quality of imported products is higher than that of Chinese equipment, the after-sales maintenance cycle of imported products is far greater than that of Chinese equipment. Generally speaking, the selection of test equipment should be based on the enterprise's own situation to choose the most ideal solution.

2、 Basic EMC test report and configuration

The EMC key test reports - test equipment - test environment (laboratory) listed in the following table are related one-to-one:

3、 EMC test equipment selection and inspection precautions

1. CE (conducted disturbance)

CE is one of the most common items in current EMC testing. Conducted disturbance refers to electromagnetic disturbance signals transmitted by wires. As for the type of disturbance signal, CE can be divided into continuous and intermittent disturbance from the port of the disturbance signal. CE can also be divided into power port, communication port and load port.

CE detection type is complex, so should we select equipment? First of all, determine the EUT to establish the corresponding specifications of the EUT, and then define the equipment required for the CE test of the corresponding test port according to the EUT. For example, for lighting equipment, the corresponding standard is GB17743 (CISPR15), which specifies CE power supply terminal, communication terminal and operation terminal detection equipment requirements, so that CE takes power supply terminal as an example, we need to use detection receiver and human power network. What basic parameters should the receiver pay attention to? The first is the detection frequency band. The detection frequency band of lighting products is 9kHz - 30MHz. The receiver must be able to meet the requirements of this frequency band, and then the bandwidth and detector must be detected. The receiver must meet the requirements of 2000Hz. 9kHz, and must include three detectors with the bandwidth of Peak. Qpeak. CAvg. In the specific use, some customers choose the spectrometer to replace the receiver for testing, but the bandwidth and detector of the spectrometer cannot meet the specifications and standards, and the test results will certainly have some deviation. For the human power grid, we should establish the port type. We choose the V-type power port LISN, and the impedance requirement is (50) uH5 Ω) ‖ 50 Ω. It is also necessary to consider that EUT selects the corresponding power supply voltage LISN according to different voltages.

What areas of CE need your attention? First, EMC test environment. EMC standard CE test must be conducted in shielded room. When selecting the initial equipment, some manufacturers usually only purchase to reduce the cost. EMC does not consider the testing equipment EMC laboratory, and places the EMC testing equipment in the extreme electromagnetic environment. The testing results are often swallowed by the deviation of the background noise, thus affecting the analysis of the testing results. The second is the layout of the machine. The CE specification layout EMC specification has already mentioned that it is necessary to achieve "two 80's and one 40's". The two 80's refer to the EUT horizontal reference floor of 80cm (that is, the height of the test bench is 80cm). The EUT spacing LISN output port is 80cm (that is, LISN is placed below the test bench). One 40 refers to the EUT floor spacing of 40cm directly. The EUT distance between LISN ports is 80cm. In practical use, the length of the cable is often more than 80 cm. You can wrap it in a zigzag way with a length of less than 40cm. Because CE belongs to the electromagnetic disturbance transmitted by cables, whether the cable layout is standardized or not is directly related to the detection results.

2. RFP (disturbance power)

At present, RFP is widely used in the household appliance industry. In essence, RFP is to detect the radiation disturbance of products. RE antenna method (radiation disturbance) should measure the EUT electromagnetic disturbance emitted from the surface through the receiving antenna, while electromagnetic disturbance. RFP (scratch power) electromagnetic absorption clamp is used to measure the electromagnetic disturbance emitted along the power line.

The RFP must check the receiver, electromagnetic absorption clamp, decoupling clamp and slide rail. The RFP detection uses the slideway and the mobile car with the electromagnetic absorption clamp to pair the EUT power line with the receiver for multi-point measurement EUT to comprehensively judge the amount of electromagnetic interference. The most important part of the RFP test equipment is the receiver. The receiver must meet the following core requirements: 1. The frequency band covers 30MHz-300MHz2. It includes 120kHz bandwidth 3. It includes three detectors, Peak. Qpeak. CAvg. In addition, when the electric guide rail is configured, a set of software is also required to facilitate the connection of the receiver and the slide rail for automatic testing. The selection and disassembly of electromagnetic absorption clamp and decoupling clamp must comply with the frequency band coverage of 30MHz-300MHz. In addition, the EUT detection current and wire diameter should also be considered.

One thing we should pay attention to when testing the specific use of RFP. Many manufacturers and even third-party testing agencies will directly fix the mobile car at the same position for testing, because it is only for convenience of testing. This operation will actually damage the test results. RFP is an alternative to RE (radiation disturbance). If the fixed vehicle only detects one location point, it is difficult to accurately reflect the specific radiation state of the EUT. Most electrical products have various internal management procedures, and the specific operating state is time domain change. The test time at the enterprise point is usually very short, which cannot reflect the specific working state of the EUT. Therefore, the detection of RFP (scratch power) requires multi-point system detection. In addition, due to the change of standards, CISPR22 specification has been replaced by CISPR32, and the RFP project has been canceled in CISPR32, but not in GB4343.1. Therefore, before selecting the test report, the customer needs to determine the requirements that the product must meet.

3. RE (radiation disturbance)

RE is one of the most expensive projects in EMC testing because the RE laboratory environment must be a semi-anechoic chamber. On the premise of shielding chamber, the semi-anechoic chamber needs to be laid with ferrite and absorbing wedge. Therefore, in addition to the shielding efficiency index, the semi-anechoic chamber also needs to meet the FU/NSA/SVSWR technical parameters. Because radiation disturbance refers to the electromagnetic disturbance signal emitted by EUT according to the surface, which needs to be measured from all directions and angles. Therefore, the antenna tower and turntable are also used inside the anechoic chamber. The antenna tower is used to control the height (1) m-4m) and polarity change (H/V) of the receiving antenna. The turntable controls the EUT rotation angle (0) ° - 360 °). The RE detects the signal in the following way: EUT-receiving antenna-receiver. Therefore, RE receiver and receiving antenna also need to be detected. The frequency range of corresponding standards such as EUT lighting products that must cover the receiver frequency band is generally 30MHz-300MHz, and it also needs to include 120kHz bandwidth and three sensors, Peak. Qpeak. CAvg. In addition, due to the connection between the turntable and the antenna tower, EMC test software is also required to connect the turntable and automatically test the antenna tower and receiver. The selection of receiving antenna is relatively simple, and the brands on the market are relatively dry. As long as we meet the requirements of receiving antenna, RE can detect the frequency band.

In the specific use of RE, we found that the radiation disturbance signal of the receiving antenna at 1 m-2 m is usually higher than 3 m-4 m. If you find that the EUT can only be tested at 1 m-2 m when this rule is really reached in many tests, this can save a lot of test time.

4. RS (radiated immunity)

The laboratory environment of RS and RE semi-anechoic chamber also needs to be used, but because RS belongs to the immunity test report, RS must have a set of standard signal generation equipment: signal source:. power amplifier, power meter, directional coupler, transmitting antenna and field strength probe. Before RS test, it is necessary to calibrate the symmetrical location, test method and FU function test. In addition, in order to ensure that the power amplifier is not saturated: the minimum field strength used for correction is 1.8 times the EUT field strength. In the calibration process, we usually use the stable field strength method to measure 1.5m × 16 points in the 1.5 m symmetric domain are calibrated. If 75% of the calibration point difference is 6 dB, the field average symmetric domain meets the test requirements. In order to achieve the completion of the field symmetry domain, we often lay the absorbing tip on the ground to achieve the effect of weakening the ground reflection. In the calibration process, the signal source first sends standard signals at the corresponding frequency points, and then derives them separately according to the directional coupler. The two directions are exported to the forward and reverse power meters respectively, and the other direction is exported to the power amplifier respectively. The power amplifier amplifies the power of the equipment, and then transmits it from the outside through the transmission antenna. Finally, the field intensity probe measures the electromagnetic interference. If the standard field strength is not reached, adjust the size of the output signal of the signal source until the standard field strength is reached. The RS test procedure is similar to the calibration, and the operation procedure is also quite simple.

5. Conclusion

EMC harmonic current is also commonly used for testing. Voltage fluctuation and flicker. Electrostatic discharge immunity. These devices are highly integrated machines. The layout of software development and software development EUT requirements is also relatively simple, and users can easily grasp them in practical applications.

With the development of electronic technology, the electromagnetic compatibility (EMC) of household electrical products has become a key quality standard, which is not only related to the working stability and application safety of the product itself, but also may affect the normal operation and comprehensive operation of other equipment. In addition, research has found that extreme electromagnetic environment can affect the nervous system, sensory system and immune system of the body, causing major harm. Electromagnetic environment is related to human life and health, and EMC has become one of the indispensable test reports for commodities.