1. Starting from firmware version V4.1, the S7-1200 CPU supports configuration control functions, making module configuration and installation more flexible.
2. Establish a dedicated and independent grounding network for the DCS system;
3. Set up a dedicated grounding network for DCS, which is connected to the electrical grounding network through a grounding wire.
Due to the many similarities between the third grounding method and the second grounding method, in the past, computer or DCS systems have often used dedicated grounding grids. However, the drawbacks of this grounding method are: large land area, high investment, high consumption of cables and grounding network steel, considerable distance from the factory building (as it is difficult to find a suitable location within the factory building), inconvenient management, maintenance, measurement, and searching for grounding electrodes and wires, and poor effectiveness. According to actual operation, setting up a dedicated DCS grounding network is both difficult and unsafe.
4、 Requirements for public grounding electrodes (grids)
1. When the distribution resistance of the electrical grounding network in the factory area to the ground is ≤ 4 Ω, the electrical grounding network in the factory area can be connected to the common grounding electrode (network) of the DCS system.
2. When the grounding resistance of the electrical grounding network in the factory area is large or disorderly, an independent grounding system should be set up, which is the common grounding electrode (network) of the DCS system.
3. The distribution resistance to ground of the public grounding electrode (network) without intrinsically safe connection is less than 4 Ω; Less than 1 Ω with intrinsic safety. The impedance of the grounding main line is less than 0.1 Ω.
4. There is no access point for lightning protection within 15 meters around the grounding electrode, and there is no access point for high and low voltage electrical equipment shells with a power output of over 30KW within 8 meters. When the site cannot meet this condition, the lightning protection ground is connected to the main line of the public grounding electrode through a lightning arrester/shock wave suppressor. The welding ground should not be overlapped with the public grounding electrode and its grounding grid, and the distance between the two should be more than 10 meters.
5、 Grounding principles of DCS system
1. Grounding device for DCS system settings
1.1 Operating desk, printing desk, server cabinet: equipped with protective screws.
1.2 Relay cabinet, UPS cabinet, and distribution cabinet: equipped with protective grounding screws.
1.3 DCS I/O cabinet: equipped with shielded grounding busbar, protective grounding screw, and system ground (+24V ground) suspension.
1.4 Instrument cabinet and manual control panel: equipped with shielded grounding busbar and protective grounding screw.
1.5 Safety barrier cabinet: equipped with shielded grounding busbar, intrinsically safe grounding busbar, and protective grounding screw.
2. Signal shielding and grounding
According to relevant technical regulations, the shielding layer of computer or DCS system signal cables must not be floating and must be grounded. The grounding method should comply with the following regulations:
2.1 When the signal source is floating, the shielding layer should be grounded on the computer side;
2.2 When the signal source is grounded, the shielding layer should be grounded on the signal source side;
When the amplifier is floating, one end of the shielding layer should be connected to the shielding cover, and the other end should be connected to common mode ground (when the signal source is grounded, it should be connected to signal ground. When the signal source is floating, it should be connected to the field);
When the shielded cable is disconnected or merged through the junction box, the shielding layers of the cables at both ends should be connected inside the junction box.