To prevent interference from electromagnetic fields in the environment from affecting the control signal lines between the PLC and the frequency converter, a shielded cable can be connected to the outer layer of these control signal lines to improve the system's anti-interference capability. It is crucial to ensure that only one grounding point is selected for the shield, regardless of whether it's on the PLC side or the frequency converter side. Generally, it should be selected at the signal receiving end, i.e., the frequency converter side. This improves the system's anti-interference capability. If the shielded cable is grounded at both ends, current will flow through the shielded cable, which will not only fail to improve the system's anti-interference capability but will also exacerbate external interference to the PLC.
The following principles should be followed when connecting shielded wires.
1. The shielding wire should be placed as close as possible to the end with the lowest potential. This can be understood as follows: we generally consider the ground potential to be "0", but in reality, if there are two grounding terminals, there will be a potential difference between the two grounding terminals at a certain moment, and current will flow between the two grounding wires, which is also a kind of interference.
2. In practical applications, if the control cable passes through complex locations and requires multiple grounding points, we generally cut the shielding layer and ground it at different locations. This method is also commonly used for grounding the shielding layer of communication cables in control equipment in large factories.
