3500/93 135785-01 of the radiated electromagnetic field (EMI) is mainly generated by the power network, electrical equipment transient processes, lightning, radio broadcasting, television, radar, high-frequency induction heating equipment, etc., usually referred to as radiated interference, its distribution is extremely complex. If the PLC system is placed in the radio frequency field, it is recycled to the radiation interference, the impact of which is mainly through two paths: one is directly to the PLC internal radiation, by the circuit inductance of the interference; but rather to the PLC communication within the network of radiation, by the inductance of the communication line of the introduction of interference. Radiation interference with the field equipment layout and equipment generated by the size of the electromagnetic field, especially frequency-related, generally through the setting of shielded cables and PLC local shielding and high-voltage relief elements for protection.

3500/93 135785-01 is mainly introduced through the power supply and signal lines, usually called conduction interference. This type of interference is more serious in our industrial sites. Practice has shown that the power supply interference caused by the introduction of PLC control system failure in many cases, I encountered in a project debugging, and then replace the isolation performance of the higher PLC power supply, the problem is solved.

3500/93 135785-01 normal power supply are powered by the grid. As the grid covers a wide range, it will be subject to all space electromagnetic interference and inductance voltage and circuit on the line. In particular, the changes within the grid, into the switching operation surge, large-scale power equipment start and stop, AC and DC drives caused by harmonics, grid short circuit transient shock, etc., are transmitted through the transmission lines to the original side of the power supply. PLC power supply is usually used to isolate the power supply, but the mechanism and manufacturing process factors that make the isolation is not ideal. In fact, due to the presence of distributed parameters, especially distributed capacitance, absolute isolation is impossible.