Simply put, logical ground means that logic circuits are connected to a common ground point and maintain the same reference potential. In practical application, under normal circumstances, the common negative pole of DCS signal circuit, the negative pole of DC power supply of signal circuit and the negative pole of logic circuit will be connected to the same grounding electrode, which should generally be set independently and keep a safe distance from the electrical grounding network.
Protective place is a protective measure to prevent electrostatic charge from accumulating in the equipment shell and avoid personal injury. All operator cabinets, field control station cabinets, printers, terminal cabinets, etc. Should be connected to the protective grounding. The protective grounding shall be connected to the electrical professional grounding network of the factory, and the grounding resistance shall be less than 4Ω.