Measurement of conducted interference voltage/current at the power supply terminals
When measuring conducted interference, the German VDE (verbenadetacherelectrotechniquer) and CISPR standards use LISN circuits that are different from the U.S. Federal Communications Commission (FCC) standard, which has an input impedance of 150, while the FCC standard uses LISN circuits with an input impedance of 50. FCC standard LISN circuit, its input impedance is 50. conducted interference test lower limit frequency, VDE and CISPR standards for 10kHz, while the FCC standard for 450kHz; these three standards provide for the upper limit frequency is 30MHz.
When measuring on a radiation test site, the EUT should be in the same state as the radiation measurement, and the EUT should be on a metal grounded flat plate that extends at least O.5m or *smaller size of 2m x 2m than its boundary.
In the case of measurement in a shielded room, the ground shield or the shield of any wall can be used as the grounding plate. During the test, the non-grounded EUT should be placed on an insulated support or table 0.4m above the grounding plate. The grounded EUT shall be placed on the grounding plate, and its contacts shall be insulated from each other or consistent with normal use. All EUTs shall be located at a distance greater than 0.8m from other metal objects.
The *proximity* between the outer surface of the LISN and the boundary of the EUT should be less than 0.8 m. The reference earth terminal of the network should be connected to the earthing flat plate with the thickest and shortest conductor possible. The correlation between the power and signal cables and the signal cable alignment and the grounding plate should be equivalent to the actual use case, and the cables should be laid out with great care to avoid false response effects. Figure 3 shows a typical arrangement for conducted interference measurements when measured inside a shielded room.
When the EUT is fitted with a special earth terminal, the earth should be connected with the shortest possible conductor. EUTs not fitted with a special earth terminal should be tested under their normal connection, i.e. obtaining an earth from the supply grid. Units supplied with flexible power cords by the manufacturer shall have power cords with a length of 1 m. If the actual length exceeds 1 m, the excess shall be folded back and forth into a bundle of O.3 to O.4 m. If the EUT consists of several units, it shall be connected to the power supply grid with as short a length of wire as possible.
If the EUT consists of several units and each unit has a power cord, the connection to the LISN depends on the following provisions:
① Each power cable connected to a standard power plug shall be measured separately; and
(ii) Power supply cables or terminals that are not specified by the manufacturer to be supplied from another unit in the system shall be measured separately.
(iii) The power supply cable or terminal specified by the manufacturer to be supplied from a unit in the system shall be connected to that unit, and the cable or terminal of that unit shall be connected to LISN for measurement; (iv) When the EUT is used for the purpose of ***, the power supply cable shall be measured separately.
(iv) When the EUT needs to be grounded for ** purposes, the grounding wire shall be connected to the reference ground point of the LISN. Except for the grounding wire supplied by the manufacturer or otherwise specified for grounding, in the absence of other special requirements, the length of the grounding wire shall be lm and shall be laid in parallel with the EUT power supply line at intervals of not more than O.1m.
