Since the 1980s, China has accelerated the pace of formulating national standards for electromagnetic compatibility . In June 1988, the national standard "GB9254 1988" equivalent to "CISPR22:1985" of the International Special Committee on Radio Interference was released. It will come into effect on January 1st. In 1993, the standard became a mandatory national standard. Later, considering the applicability and timeliness of the standard, GB9254 1988 was revised according to the third edition of "CISPR22:1997", and the implementation date was December 1, 1999. This standard will replace GB9254 1988 from the date of its implementation, but the implementation of the content related to the telecommunications port will be delayed by half a year. This standard is still implemented as a mandatory standard. At the same time, GB/T17618 1998 "Information Technology Equipment Immunity Limits and Measurement Methods" was released. This standard is equivalent to "CISPR24:1997" and is implemented as a recommended standard. The two national standards for electromagnetic compatibility products The release will provide a technical basis for the formulation of domestic information technology equipment product standards.
1. Definition of information technology equipment
Information technology equipment is one of the most important terms in GB9254, which defines the applicable scope of this standard. 3.1 of GB9254 gives a clear definition:
information technology equipment is any equipment that satisfies condition (a) and condition (b) at the same time;
(a). Capable of entering, storing, displaying, retrieving, transmitting, exchanging, or controlling (or a combination of) data and telecommunications messages; the equipment may be provided with one or more terminal ports normally used for information transmission ;
(b). The rated voltage does not exceed 600V.
According to the use environment of the product, information technology equipment is divided into Class A and Class B. They must meet Class A and Class B EMC standards respectively, and Class B standards are stricter than Class A standards. Generally speaking, information technology equipment used in the following places belongs to Class B;
- Residential areas, such as courtyard houses, apartments, etc.;
- Commercial areas, such as shops, supermarkets, etc.;
- Business areas, such as office buildings, banks, etc.;
- Public entertainment places, such as cinemas, restaurants, discos, etc.;
- Outdoor places, such as gas stations, parking lots and sports centers, etc.;
- Light industrial areas, such as workshops, laboratories, etc.
Products that meet Class A electromagnetic compatibility standards usually declare the following content on the instruction manual or product label:
"This product meets electromagnetic compatibility class A. In the living environment, this product may cause radio disturbance. In this case, users may be required to take practical measures against the disturbance."
2. Limits
2.1 Conducted disturbance limits of power terminals
Electromagnetic disturbance can be transmitted through the power terminal of the equipment, causing pollution to the power grid. Therefore, the electromagnetic compatibility standard restricts the conducted emission of the power terminal, which is the limit value of the conducted emission of the power terminal. Table 2 shows the conduction disturbance limits for Class A and Class B power terminals.
Table 2 Conducted disturbance limits of power terminals
| Grade A |
Grade B |
||||
| Frequency RangeMHz |
Limit dBμV |
Frequency Range MHz |
Limit dBμV |
||
| quasi-peak |
average value |
quasi-peak |
average value |
||
| 0.15 ～ 0.50 |
79 |
66 |
0.15 ～ 0.50 |
66 ～ 56 |
56 ～ 46 |
| 0.50 ～ 50 |
78 |
60 |
0.50 ～ 5 |
56 |
46 |
| 5 ～ 30 |
60 |
50 |
|||
2.2 Common mode conduction disturbance limits for telecommunication ports
The common mode current on the cable will produce strong electromagnetic radiation. Most of the equipment can pass the relevant standards without connecting to the telecommunication cable, but after connecting the cable, it will no longer meet the requirements of the standard. This is due to the common mode of the cable. The current produces common-mode radiation. Therefore, this item puts forward restrictions on the common-mode conducted emission of telecommunication ports, and Table 3 gives the common-mode conducted disturbance limits of A-level and B-level telecommunication ports.
| Frequency RangeMHz |
Grade A |
Grade B |
|||||||||
| Voltage limit dBμV |
Current limit dBμA |
Voltage limit dBμV |
Current limit dBμA |
||||||||
| quasi-peak |
average value |
quasi-peak |
average value |
quasi-peak |
average value |
quasi-peak |
average value |
||||
| 0.15 ～ 0.5 |
97～87 |
84～74 |
53～43 |
40～30 |
84～74 |
74～64 |
40～30 |
30～20 |
|||
| 0.5 ～ 30 |
87 |
74 |
43 |
30 |
74 |
64 |
30 |
20 |
|||
2.3 Radiated Emission Disturbance Limits
Information equipment will radiate electromagnetic waves into the space when it is working, which constitutes a disturbance to other equipment, especially a great impact on wireless receiving equipment. Therefore, this item places limits on the intensity of electromagnetic waves radiated by the equipment. Table 4 shows the limits for Class A and Class B radiated disturbances.
Table 4: Radiated Disturbance Limits
| Frequency Range MHz |
Quasi-peak dBμV/m |
|
| Grade A |
Grade B |
|
| 30～230 |
40 |
30 |
| 230～1000 |
47 |
37 |
2.4 Immunity limits of the chassis
The chassis must have a certain resistance to various external disturbances. According to the disturbances in the actual environment, they are divided into three categories as shown in Table 5.
Table 5: Chassis immunity test limits
| Electromagnetic environment |
Immunity limit |
| Power frequency magnetic field |
50 or 60Hz 1A/m (rms) |
| radio frequency electromagnetic field |
≤80 ~ 1000MHz 3V/m (rms, unmodulated) 80% AM (1KHz) |
| electrostatic discharge |
4KV (contact discharge) 8KV (air discharge) |
2.5 Signal ports and immunity limits
The disturbance on the signal port comes from the current induced by space electromagnetic waves on the cable. According to the electromagnetic disturbance phenomenon in the actual environment, there are three types shown in Table 6.
TABLE 6: SIGNAL PORT AND TELECOM PORT IMMUNITY LIMITS
| Electromagnetic environment |
Immunity limit |
| RF continuous wave conduction |
0.15~80MHz 3V (rms, unmodulated) 80% AM (1KHz) |
| surge (shock) |
1.5KV (peak value) 4KV (peak value) 10/700μs |
| EFT |
0.5KV (peak value) 5/50ns 5KHz (repetition frequency) |
2.6 Immunity Limits for DC Power Ports
The immunity requirements of the DC power port are shown in Table 7.
TABLE 7: IMMUNITY LIMITS FOR POWER INPUT PORTS
| Electromagnetic environment |
Immunity limit |
| RF continuous wave conduction |
0.15~80MHz 3V (rms, unmodulated) 80% AM (1KHz) |
| surge (shock) |
1.2/50 (8/20) μs 0.5KV(peak value) |
| EFT |
0.5KV (peak value) 5/50ns 5KHz (repetition frequency) |
2.7 AC Power Port Immunity Limits
The immunity requirements of the AC power port are shown in Table 8.
Table 8: AC Power Port Immunity Requirements
| Electromagnetic environment |
Immunity limit |
| RF continuous wave conduction |
0.15~80MHz 3V (rms, unmodulated) 80% AM (1KHz) |
| voltage sag |
>95% reduced by 0.5 cycle 30% reduced by 25 cycles |
| short interruption of voltage |
>95% reduce 250 cycles |
| surge (shock) |
1.2/50(8/20) μs 1KV (peak), line 2KV (peak), line ground |
| EFT |
1.0KV 5/50ns 5KHz (repetition frequency) |
3. Measurement method
3.1 Measurement method of conducted disturbance at power terminals
3.1.1 Measuring equipment
Three pieces of equipment are required to perform conducted emissions measurements at power terminals:
- Disturbance measurement equipment: The equipment used to quantitatively measure the disturbance intensity can be an EMI measurement receiver or a spectrum analyzer. The frequency range should cover 150KHz~30MHz, with peak, quasi-peak and average detection functions, meeting GB/T6113 .1 Specified requirements.
- 线路阻抗稳定网络（LISN）：由于电源端子传导发射的强度与电网的阻抗有关，因此为了使测量具有唯一性，必须在特定的阻抗条件下测量，LISN就提供了这样一个环境，GB9254标准中使用的LISN为50Ω/50μH，要满足GB/T6113.1第8章规定的要求。
- 接地平板：受试设备要放置在接地金属板上进行试验，该金属板比被测设备边框大0.5米，最小尺寸为2m×2m;
3.1.2测量方法
电源端子传导骚扰测量主要测量被测设备沿着电源线向电网发射的骚扰电压，做这项试验时要注意的是：调整受试设备工作状态，找出最大骚扰所对应的工作状态为试验结果。
3.2电信端口共模骚扰测量方法
3.2.1测量设备
进行电源端子传导发射测量需要4种设备：
- 骚扰测量设备：用来定量计量骚扰强度的设备，同电源端口传导发射测量的要求相同。
- 阻抗网络：共模终端阻抗为150Ω±20Ω，相角0°±20°；隔离度在150KHz 1.5MHz为35 55dB，随频率线性上升，在15 30MHz时大于55dB；纵向转换损耗对3类电缆150KHz 1.5MHz为80 55dB±3dB，1.5 30MHz时大于50 25dB±3dB，并随频率线性下降；
- 容性电压探头：阻抗 ＞ 1MΩ，并联电容 ＜ 5pF；
- 电流探头：插入阻抗≤1Ω；
- 接地平板比被测设备边框大0.5m，最小尺寸为2m×2m。
3.2.1测量方法
电信端口配置为两组以上平衡对线或非屏蔽电缆时，采用电压法和电流法；
电信端口配置为平衡电缆或同轴（屏蔽）电缆时，采用电流法。
详见GB9254附录C。
3.3辐射骚扰测量方法
3.3.1测量设备与场地
- 椭圆形开阔场或半电波暗室，水平和垂直场地衰减测量值与理想场地的理论值之差不得大于±4dB；
- 测量接收机：30 1000MHz，满足GB/T6113.1；
- Antenna : logarithmic dipole antenna or biconical antenna, meeting GB/T6113.1;
- Ground plane: comply with GB/T6113.1;
3.3.2 Measurement method
Take the horizontal polarization direction of the antenna and place it at an appropriate height, place the turntable at an appropriate angle, and use peak detection in the range of 30 to 1000MHz for initial measurement;
Rotate the turntable between 0° and 360°, and find the maximum disturbance level (quasi-peak value) of the device under test at the frequency point where the disturbance is relatively large during the initial measurement;
Lift and lower the antenna within the height range of 14m to find the electrical disturbance level at this frequency point;
Change the antenna polarization direction to vertical polarization, and repeat the above measurement.
3.4 Electrostatic discharge immunity test
Number of discharges and location: 200 discharges are performed on the equipment under test, 150 of which are directly contacted at 3 test points, and the other test point is selected at the center of the front edge of the horizontal coupling plate for 50 indirect discharges . At least 10 single air discharges shall be performed at each test point in the gap;
Discharge polarity: carry out positive and negative electrostatic discharge.
3.5 Radio Frequency Electromagnetic Field Radiation Immunity Test
Frequency range: 80 1000MHz;
Test signal: 80% amplitude modulation of the test signal with 1KHz sine wave;
3.6 Electrical fast transient burst immunity test
When the equipment has multiple identical ports, only one of them is tested; multi-core cables are tested as a single cable; data cable ports not exceeding 3m in length are not subject to this test.
3.7 Voltage sag, short interruption and voltage change immunity test
The test voltage sag is stipulated as two levels of cycle > 95% and 30%, corresponding to two different test cycles: 0.5 and 25.
3.8 Conducted disturbance immunity test induced by radio frequency field
Apply only 3Vrms (unmodulated) test voltage to the EUT.
3.9 Surge (shock) immunity test
0.5KV (line ground) disturbance voltage is applied to the DC power port (only suitable for the port directly connected to the outdoor cable);
1KV (line) and 2KV (line ground) disturbance voltages are applied to the AC power port; 1.5KV and 4KV disturbance voltages are applied to the signal and telecommunication ports directly connected to the outdoor.
For the above immunity test methods, please refer to GB/T17618 1998 and GB/T17626.