853-064940-206 There will be some precautions in EMC experiments, and each EMC engineer has different operation methods, especially the position of the wiring harness and the position of the machine during the test, and it is often some small details that lead to EMC test problems, such as the wiring harness placement problem in EMI test we talked about today. For the machine wiring harness placement is also a more important part of the experiment, different placement and wiring harness placement will have different test results.

Two-radiation antenna

853-064940-206 Due to the problem of radiation emission, a large part of the problem is caused by the interference conduction or coupling of PCB to the wire harness, which is radiated through the wire harness and then received by the antenna, forming EMI interference, resulting in EMI experiments that cannot pass the test standards. During laboratory testing, engineers will debug and place EUT. Under certain working modes, different placement of wire harnesses will lead to different test data. The placement of wire harnesses will be vertical or horizontal. When the wiring harness is vertical and the antenna direction is also vertical, the energy received by the receiving antenna will be relatively large; The same is true for the horizontal direction.

853-064940-206 The influence of EUT body structure, cable, port, PCB, signal type, etc., leads to the generation of different types of polarized waves, including waves in the vertical and horizontal polarization directions, where the energy size is different, and the polarization loss generated on the receiving antenna is different. When the polarization direction of the incoming wave is inconsistent with the polarization direction of the receiving antenna, the received signal will become smaller, that is, the polarization loss occurs.

Three test data comparison

853-064940-206 Sometimes our measured machine equipment EUT power harness, and the wiring harness connected to the auxiliary equipment is relatively long, if the wiring harness is not tied or the wiring harness is still too long after tying, the noise interference of the machine will radiate out through these long wiring harnesses, so sometimes the length of the wiring harness can be determined, and the wiring harness connected with the EUT is preferred to be as short as possible.

When the wiring harness of the device under test is too long, it is necessary to fold and place the wiring harness according to the test standard. There is such a case that the test data will be different due to the different folding mode and length of the wiring harness, and too long wiring harness will directly lead to the failure of the experiment results. We made an experiment comparison, when the center of the wiring harness is bundled into 50cm length and 10cm length, under the same working mode and other test conditions, the comparison data can be seen that the data of 50cm bundled wiring harness is worse than that of 10cm bundled wiring harness.