1. Change the soil structure around the grounding body. Within a range of 2-3 meters of soil around the grounding body, adding substances that are not suitable for water and have good water absorption, such as charcoal, coke cinder, or slag, can reduce the soil resistivity to 1/5-1/10 of the original value.
2. Use salt and charcoal to reduce soil resistivity. Use salt and charcoal to compact in layers. Mix charcoal and fine mixture into a layer, about 10-15cm thick, and then lay 2-3 cm of table salt in a total of 5-8 layers. After laying, drive in the grounding body. This method can reduce the resistivity to 1/3 to 1/5 of the original value. But over time, salt will run off with running water, and it usually needs to be replenished once every two years.
3. Use long-term chemical drag reducing agents. The use of long-term chemical resistance reducing agents can reduce soil resistivity to 40% of its original value.
7、 DCS system grounding materials and requirements
1. Material requirements for grounding body and grounding grid main line
2. 2. Requirements for grounding connection
The protective and shielding grounding connections of the DCS system should be connected to the dedicated electrical grounding network or grounding body in the factory area using copper core insulated wires or cables. When the grounding connection distance is long, the DCS system requires high grounding resistance, or there are many branch lines to be connected to the grounding main line, it is advisable to choose wires and cables with larger cross-section in the table.
8、 Common precautions for on-site grounding
1. On-site control station
The grounding screw is insulated due to the presence of rubber between the cabinet body and the base, and the shielding grounding busbar is insulated from the base. The on-site control station must carry out grounding treatment according to regulations. Connect to the grounding busbar of the on-site control station separately. The power ground of the I/O cabinet and the power ground of the UPS must be connected to the same ground to ensure equal potential.
2. Various hardware devices
The operator station, engineer station, network switch, server host, system display, etc. shall be grounded by the casing or directly connected to the electrical grounding network.
3. I/O components
The 40 terminal of the analog module, which is the negative terminal of DC 24V, is connected to the logic grounding busbar, which is then connected to the shielding ground and connected to the main grounding busbar.
4. Shielded ground
The protective ground of the on-site control station should be connected from the grounding screw below the cabinet to the grounding branch line, and the shielding ground of the on-site control station should be connected from the grounding busbar to the public connection board.
5. Grounding resistance test
The resistance of the grounding system must be tested to ensure that the grounding meets the requirements of the control system manufacturer.