Where is the optimal installation location for the magnetic ring of the power measurement switch (PMS)?

Adding a ferrite bead (or common-mode choke) to a PMS system is an economical and effective method to suppress cable radiation and conducted noise, but its effectiveness is heavily dependent on the installation location. The optimal location follows the principles of "close to the interference source or sensitive point" and "encircling all interference current." For power lines, the ferrite bead should be installed inside the PMS chassis outlet, as close as possible to the wall penetration terminal. This suppresses noise radiation from inside the chassis and attenuates external interference. For communication lines (such as RS485), the ferrite bead should be installed behind the port connector, ensuring that the signal line and return line (ground line) pass through the center of the ferrite bead simultaneously to form a common-mode choke. If the cable already has a shielding layer, the ferrite bead should be installed outside the shielding grounding point. For multi-core cables, all cores can be wound together around the ferrite bead 2-3 times to increase inductance, but attention should be paid to the distributed capacitance caused by the winding. Typical ferrite bead selections include PBZ1608E600Z0T (surface mount) or CMZ1211-501T (internal mount). By installing a suitable ferrite core at the optimal point, 10-20 dB of common-mode insertion loss can be obtained on the cable, effectively solving the problems of excessive radiated emissions or radio frequency field immunity.