Conducted interference (CE)

3. Conducted interference (CE)
Conducted emission overview
Conducted emissions are also often referred to as disturbance voltage tests. As long as the products with power cords are involved in conducted emission testing, including many DC-powered products, in addition, signal/control lines also have conducted emission requirements in many standards, usually with harassment. The limit of the voltage or disturbance current (both have a mutual conversion relationship) indicates that the insertion loss test (in dB) is also in the conduction test category.
Conducted emission test standard
CISPR22 (ITE), EN55022, GB9254CISPR14-1 (Home Appliances and Tools), EN55014-1, GB4343
CISPR13 (AV), EN55013, GB13837
CISPR15 (lamp), EN55015 GB17743CISPR11 (ISM), EN55011
GB/T 18268
GB 4824
Conducted emission test method
1) Conducted emission test instruments and equipment: receiver, LISN (line impedance stabilization network, or AMN artificial power network), analog hand, passive voltage probe, current probe (CDN used with current probe, capacitive voltage probe) , DIA (intermittent interference analyzer, used to test intermittent interference in CISPR14-1), a complete set of equipment for measuring insertion loss, of course, PC is also essential, DIA needs to comply with CISPR16-1-1 requirements, other Auxiliary equipment needs to comply with the requirements of CISPR16-1-2.
2) Conducted emission test arrangement: sub-desktop and floor-standing, desktop equipment is separated from LISN 80cm, 40cm away from the ground plane (the grounding plate here can be a horizontal grounding plate, or a vertical grounding inner wall of the shielding room), the floor-standing equipment is away The grounding plate distance has different deviations with different standards. CISPR14-1, 15 is 10cm +/- 25% inside, 13 is up to 12mm, 22 is up to 15cm, 11 is not clear distance, only said the need It is separated from the grounding plate by an insulating material. The arrangement of the auxiliary equipment also differs according to the test standard. The auxiliary equipment in CISPR22 is 10cm away from the main equipment, and the interconnection line between them is at least 40cm away from the ground plane. Handheld Class II devices require a package simulator. Self-ballasted fluorescent lamps in CISPR15 need to be housed in an auxiliary tapered metal cover.
3) Conducted emission test frequency band: mostly 150kHz-30MHz, CISPR15 is the exception (disturbance voltage 9kHz-30MHz, insertion loss 150kHz-1, 605kHz).
4) Conducted emission test limits: different product categories (Group 1/2, Class A/B) with different standards depending on different standards.
5) Conducted emission test process:
a) AC/DC power supply disturbance voltage: This is the most common, the power plug is connected to the LISN, the receiver RF input is connected to the RF output of the LISN (possibly inserted into the RF attenuator or pulse limiter), switching the LISN The L/N switch selects the common mode disturbance voltage to the ground of the test power line.
b) Intermittent interference: CISPR14-1 and some standards that refer to CISPR14-1 are required. Intermittent interference analyzers are often used in conjunction with LISN measurements. The standard also allows the replacement of a combination of an oscilloscope and a receiver. The oscilloscope observes the duration of the disturbance and the receiver observes the magnitude of the disturbance level.
c) Load side disturbance voltage: Required in CISPR14-1, CISPR15 and CISPR11. Use a passive voltage probe to insulate the load line to be tested and directly measure the disturbance voltage of the load line wire terminal to the ground with the probe and the receiver. In addition, if the rated current of the device is too large and no suitable LISN is available, the voltage probe can be used directly to measure the disturbance voltage at the power supply.
d) Communication line disturbance voltage / disturbance current: mentioned in CISPR22. There are different test methods for different types of communication lines. Annex C is described in detail, and Annex F has advantages and disadvantages in various methods. It mainly relies on different combinations of current probes and CDN, 150 ohm grounding resistance and capacitive voltage probes to test different types of communication cables. The prerequisite for ensuring the impedance of the test cables is 150 ohms. The result can be directly expressed by the disturbance current dBuA, or converted to the disturbance voltage dBuV, and the converted impedance is 150 ohms, that is, the difference between the two values is 44 dB.
e) Insertion loss: mentioned in CISPR15. The value of the insertion loss is obtained by using an RF sine wave generator through a balun, an analog lamp, a LISN, and finally measuring the comparison voltage with a receiver.
Conducted emission test result determination
The measured value (QP/AV) of the receiver detector is compared with the limit line, which is lower than the limit line PASS and higher than FAIL.
Conducted emission test considerations
Conducted emission test is a common mode disturbance measurement to the ground, so the key is in the test arrangement, the conducted emission test arrangement is no problem, and the receiver can be measured, and the difference in the conduction emission test arrangement will lead to the result. Unresolved issues: the use of the receiver RF input pulse limiter: some test mechanisms use to protect the receiver; some resist, think that the limiter contains nonlinear components to limit the pulse, resulting in intermodulation distortion and harmonic generation The wave form of harassment affects the test results. Personal opinions should not be used as much as possible, although no actual comparisons have been made.
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