Why do we need to make electronic devices? EMC electromagnetic compatibility testing, how to conduct EMC testing, from start to finish is hardware. PCB electronic design is an important aspect for engineers. According to statistics, in the vast majority of countries around the world, before becoming qualified electronic products and circulating in the market, radio and telecommunications products should undergo electromagnetic compatibility (EMC) testing. The purpose of the EMC testing process is to ensure that the interference signals transmitted by the product are within an acceptable range and to ensure that your product and functionality are not adversely affected by the interference signals.

Electromagnetic compatibility (EMC) is so important, what do we need to do in project testing for EMC products?

A complete product project EMC testing includes the following process:

EMC Radiation Emission Test: Interference Signal Measurement (EMI) Testing Based on Electrical Equipment

EMC anti-interference test: measures the sensitivity of a product to electromagnetic interference from other sources.

Electrostatic discharge (ESD) test: When two objects come into contact, static electricity is released. ESD examples include feeling static electricity after drying clothes in a clothes dryer or lightning.

Conducted immunity test: Introduce current into the input and output cables of the tested system.

Conducted emission test: RF energy transmitted from electrical equipment to the electrical system through power lines.

Frequency compatibility test: Frequency is the effective number of times electromagnetic radiation energy affects communication. The testing we provide focuses on ensuring that the normal operation of the antenna connected RF receiver/transmitter subsystem running in the system does not result in a decrease in the level from antenna to antenna.

Today we will explain in detail the EMC radiation emission test Conducted emission test.

EMC Testing - Radiated Emission

Definition: The radiation interference intensity of key radiation emission test equipment to the outside world during normal operation should be arranged according to the typical installation requirements of the client, and the cables should follow the length and model specified in the specifications; Except for the equipment specified in 36.201.1a, other equipment and systems should be based on GB4824 (Industrial) Scientific and Medical (ISM) Classification Equipment Disturbance Characteristics Limits and Measurement Methods Classification and testing.

Category: Radiated emissions with frequencies ranging from 9kHz to 18GHz

Measure the magnetic field H in this frequency band, and when the EUT is small, place it on a large magnetic ring antenna (LLA) to measure the induced current disturbance magnetic field; When the EUT is large, choose the far antenna method and measure the magnetic field strength of the disturbance at a specified distance using a single small loop.

To measure the electric field E below 1 GHz in this frequency band, which is between 30 MHz and 1 GHz, the equipment required is roughly as follows: choose a wide area or a semi anechoic chamber, simulate a semi free space, a wooden table with a height of 00.8m, a 360 degree rotating turntable, measure a distance of 360.10m, and conduct antenna vertical and horizontal polarization tests, broadband antennacoaxial cable50 disturbance detectors Ω paired transmission system, antenna impedance The coaxial impedance and the input impedance affecting the detector should be the same. Impedance mismatch can cause reflection, generate standing waves, and jeopardize the accuracy of readings. Distinguish the characteristics of the disturbance detector and select quasi peak or peak measurement.

Above 1GHz, i.e. 1GHz to 18GHz, the areas where equipment is required are roughly as follows:RS TestIn the simulation of free space, the receiving antenna is set at the same height as the EUT, and the turntable still needs to rotate 360 degrees. The test spacing is 360 degrees. A small aperture fixed antenna is selected to measure both horizontal and vertical situations. The minimum distance between the antennas should exceed 25cm. To avoid affecting antenna performance, a spectrum analyzer with large maintenance mode and most dB dynamic displays are selected for strong peak or average value identification of measurement results (no quasi peak value is required). When measuring the peak value, 1MHz is selected. In the mean measurement, the resolution bandwidth and video bandwidth are still 1MHz, but the video bandwidth should be greatly reduced to 10Hz, which is equivalent to adding a low-pass filter.

Process the antenna and receiver at a distance of 3m from the EUT (test equipment) wall, and adjust the antenna core to a height of 2m above the ground; Firstly, turn off the testing equipment and test the ambient noise level; Open the testing equipment and adjust the wiring method (including antenna height) Select a larger radiation point based on the polarization direction of the antenna and the viewing angle of its turntable; Test the different functions of equipment and search for larger radiation modes; Rotate the antenna and test the horizontal and vertical radiation disturbances separately; Using testing equipment as the core mobile antenna, select as many testing points as possible for measurement; Select radiation level as the measurement result; The experiment can be conducted in a wide field and a semi anechoic chamber; Turn off the device.

EMC Testing - Conducted Emissions

Conducted emission testing, commonly known as CE or conducted disturbance, refers to a system that measures the internal voltage or current of a signal cable The electromagnetic phenomenon where power lines or grounding wires become sources of interference for other software or devices. Conduction and emission testing is commonly referred to as disturbance voltage testing. As long as there is a power cord, it will involve products, including many DC power products. In addition, in many specifications, signal/control lines also need to be transmitted and emitted, which is usually represented by limitations on disturbance voltage or disturbance current (which are interrelated).

EUT should be placed on a strong test bench with a distance of 80 degrees to 90cm from the road surface. The surface of the test bench should be a conductive or non-conductive plane, and a metal grounding plate should be laid. This is generally the environment in which EUT is actually used Choose a conductive or non-conductive test bench for the address. For example, portable devices can be placed on non-conductive test benches, while equipment installed in ship warehouses should be tested on metal conductive test benches. Receive the power line under test based on the stable network of power impedance. The cables to be tested can be placed according to standards and laid in different lengths.

The experimental configuration for the conduction emission experiment standard of Taiwan type equipment is as follows.

① Extra long cable, folded into 30~40cm bundles;

③ EUT andLISNThe projection distance of ground spacing is 80cm;

④ The distance between each cable and GND should be at least 10cm;

⑤ The distance between the hanging cable end and GND should be 40cm or more to ensure that there is not too much coupling space.

The experimental configuration of the vertical equipment experimental standard is as follows.

③ EUT and GND should be insulated;

④ The spacing between each cable and GND should be at least 10cm (this has a significant impact as the common mode current in the cable can vary greatly).

The purpose of conducting and emitting experiments is to comply with unified standards (limits) and electronic devices power cord. Evaluate and standardize the level of conducted electromagnetic interference emitted outward by control lines or ground wires.

When the noise frequency of electronic devices is below 30MHz, it significantly affects the audio frequency range. For this low-frequency electromagnetic wave, the cable of electronic devices has a wavelength of 10m instead of 30 MHz, and its radiation efficiency to the air is very low. In this way, if the induced noise voltage on the cable can be measured, the level of electromagnetic noise impact in that frequency band can be considered. This kind of noise isConducted noiseLike interrupt noise Iron. Washing machine. The clicking sound of the rice cooker. The measured impact noise here only applies to the continuous disturbance voltage within the 30 MHz frequency test. As shown in Figure 1.1, the experimental equipment is used for conducting interference tests on the input port. The LISN linear impedance stabilization network, EUT as the experimental equipment, and LOAD as the load on the output port are used. Figure 1.2 shows the experimental equipment used for conducting interference tests on the output port.