Issues with the instrumentation control grounding resistance
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I’m not from the process control field; yesterday, I saw the field instrument technicians at work and noticed that they had connected a grounding resistor to the main control cabinet, claiming it was to prevent electromagnetic interference. And it must be less than 1 ohm. Why must it be less than 1 ohm? Can’t it be 1.5? Another thing: can electromagnetic interference be conducted away through the ground? I’ve only heard that the leakage current from the motor is directed to ground!
This is the working area, as well as the protection area – which is what you refer to as \"the grounding of the leakage current from the motor.\"
There are specific design specifications for instrument grounding, which can be found on this forum
There are over 20 pages of content that is too complicated; I’m not from an electrical engineering background. I hope those who understand the subject can explain it in a concise manner, especially why the value is 1 ohm
Minimize the interference of static electricity and leakage current on the instrument signals. . . . However, it should be stated as follows: the grounding resistance of the instrumentation and control systems is the power-frequency grounding resistance, and it should not exceed 4 ohms. The grounding connection resistance of the instrumentation and control systems should not exceed 1 ohm
Who can explain in detail what work grounding and protective grounding are? Power frequency resistance, grounding resistance! I don’t understand! :Q :Q
The ground resistance must be less than 1 ohm. This is determined by the installation and operation requirements of the instrumentation equipment; for example, devices such as DCS systems, PLCs, and other communication systems require an impedance of less than 1 ohm.
Grounding mainly refers to the working ground (the shield grounding of cables) and the protective ground (the grounding of cabinets). Do you understand?
This seems to be the second time I’m correcting this: The new standard SH/T 3081-2003, Code for Design of Grounding in Petrochemical Instrumentation (with explanatory notes), at http://bbs.hcbbs.com/viewthread.php?tid=7780&highlight=3081, clearly specifies the difference between grounding resistance and connection resistance； Only the connection resistance is required to be less than 1 ohm. The requirements for the grounding electrodes/systems under the new standards have undergone significant changes; ultimately, the automation/instrumentation systems are connected to the electrical system through grounding electrodes, busbars, etc., sharing the same ground connection. Friends who are frequently involved in projects and construction should remember to check the new standards, as this can help reduce costs significantly.
Working ground is the ground used to prevent signal interference, while protective ground is the ground that safeguards the safety of people and equipment
Instrument grounding is mainly divided into working grounding and protective grounding. Working ground (or system ground) includes: instrument signal circuit grounding and shielding grounding. Its main function is to provide a common potential reference point for each circuit, thereby preventing interference. Additionally, the grounding of intrinsically safe systems can also be included. The working ground resistance should not exceed 4 ohms. In the past, some DCS manufacturers required that the system ground resistance be no more than 1 ohm, but this requirement is no longer enforced; a value of over 4 ohms is sufficient. Protective grounding is a type of grounding designed to ensure personal safety and equipment safety, with a grounding resistance not exceeding 10 ohms. There is also anti-static grounding, with the grounding resistance generally not exceeding 100 ohms.
Grounding mainly refers to the working ground (the shield grounding of cables) ~~~~~~~~~~~~~~~~ That’s far too incomplete; it should include, as mentioned above, the grounding of instrument signal circuits, shield grounding, and the grounding of Zener safety barriers
The required value for ground resistance varies depending on the different DCS manufacturers used in the control room； General specifications require less than 4 ohms. The main purpose of grounding is to prevent electrostatic interference ； This is due to the types of interference, such as electromagnetic interference, static electricity, and lightning strikes, and it is determined by the material of the shielding layer and the grounding method.
The specification for floor 5 comes from SH/T 3081-2003, that’s correct.