Questions about EMC, and EMC testing

Electromagnetic compatibility (EMC) is a discipline that studies how various electrical devices (generally including organisms) can coexist without degrading under limited conditions of space, time, and spectrum resources. It includes electromagnetic interference and electromagnetic sensitivity. The electromagnetic interference test measures the magnitude of the electromagnetic wave signal generated and emitted by the device under test under normal working conditions to reflect the strength of the surrounding electronic equipment. The electromagnetic sensitivity test measures the immunity of the device under test against electromagnetic disturbances. Electromagnetic interference mainly includes radiation emission and conduction emission. In other words, what we want to study is that the compatibility of electronic and electrical products is mutually exclusive, that is, they do not interfere with each other and will not cause any degradation of system performance due to interference from any of the other electronic appliances. When you use a hair dryer or start any electric device with a built-in motor, there is clutter on the monitor screen. When the image is disturbed and the sound is heard on the sound, the phone suddenly sounds a “beep” due to an incoming call from the mobile phone. These are all electronic products. Incompatibility resulted.

EMC certification of electrical products 

The EMC inspection project includes electromagnetic emission (EMI) and electromagnetic immunity (EMS).

Electromagnetic emission (EMI) inspection items include:

1. Continuous interference voltage (150kHz ~ 30MHz);

2. Intermittent interference voltage (clicks) (150kHz, 500kHz, 1.4MHz, and 30MHz);

3. Interference power (30MHz～300MHz)

4. Harmonic current (2-40th harmonics)

Electromagnetic immunity (EMS) test items include:

1. Electrostatic discharge immunity;

2. Radiation electromagnetic field (80MHz ~ 1000MHz) immunity;

3. Electrical fast transient/burst immunity;

4. Surge (lightning strike) immunity;

5. Injected current (150kHz ~ 230MHz) immunity;

EMC certification standards

1. GB 4343-1995 "Measuring methods and permissible values of radio disturbance characteristics of household and similar electric, electric appliances, electric tools and similar electrical appliances", which was issued on August 25, 1995 and implemented on December 1, 1996. .

2. GB4343.2-1999 “Electromagnetic Compatibility with Household Appliances, Power Tools, and Similar Appliances Requirement Part 2 Immunity” This standard was issued on March 23, 1999 and implemented on April 1, 2000.

3. GB 17625.1-1998 "Harmonic current limits issued by low-voltage electrical and electronic equipment (equipment with equipment current of £16A per phase)" This standard was issued on December 14, 1998 and implemented on December 1, 1999. . At present, the standard is encouraged to adopt. If it fails, it will not be the basis for the overall judgment of the certification.

EMC Certified Sampling and Decision Rules

1. Randomly select 4 samples from 30 to 50 sampling mothers, of which 3 samples are used for inspection and 1 sample is used for the company's reserve for future reference. If the number of mothers is greater than 50, 50 samples can be randomly selected as sampling parents. .

2. The company randomly selects one sample from the three samples used for inspection and sends it to the designated EMC laboratory for inspection. The inspection result is judged according to the limit specified in the implementation standard of the certification by 2 dB.

3. If the measurement result of a single sample satisfies the strict 2dB limit specified by the certification implementation standard, the sample is judged as qualified.

4. If the measurement result of a single sample does not meet the requirements of the limits specified in the certification implementation standards, the sample inspection shall be judged as unqualified.

5. If the measurement result of a single sample satisfies the requirements of the limits specified in the certification implementation standards, but does not meet the strict 2dB limit as specified in the certification implementation standards, the company shall send the other two samples taken for inspection to the testing organization for inspection. If the results of the 2 samples submitted for inspection meet the requirements of the limits specified in the certification implementation standards, the samples shall be judged to be qualified, otherwise, the samples shall be judged as unqualified.

First, it is best to choose powerful companies. At present, there are some domestic manufacturers in the society for two or three people. You should be cautious when purchasing such manufacturers.

Second, buy suitable for their own products, in fact, many domestic manufacturers EMS test equipment to do a good job. . Because too expensive instruments can bring financial burden on the company. So compare a lot when you purchase the instrument.

Third, after-sales service guarantee. Service is a key issue for EMC test instruments. Because many technicians are still unfamiliar with EMC, there are more or less minor problems.

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