Casos de empresas sobre Instrument Grounding: Critical for Instrument Reliability – A Comprehensive Guide
Instrument Grounding: Critical for Instrument Reliability – A Comprehensive Guide
2025-10-13
Instrument grounding is used to address safety issues of the instrument equipment itself and the safety of operators, while also ensuring a reliable reference potential point for the instrument. Typically, the reference ground is pre-determined inside the instrument.
Functions of Grounding
Safety Grounding for Instruments: Without grounding, if the insulation performance of the power supply part deteriorates, safety hazards will arise. After the instrument is grounded, it maintains a zero potential at all times. Even in the event of internal leakage, the leakage current will be discharged to the ground wire, causing no harm to instrument operators and ensuring personnel safety.
Static Charge Discharge: Grounding can discharge the charges accumulated due to electrostatic induction, thereby preventing internal discharge caused by elevated circuit potential in the instrument due to charge accumulation.
Enhanced Operational Stability: It improves the operational stability of the instrument and prevents circuit instability caused by changes in the instrument's potential relative to the ground potential under external electric, magnetic, or electromagnetic fields. Grounding the instrument housing can effectively prevent interference.
Grounding Resistance Value
For general instrument grounding, the resistance value should not exceed 4 ohms.
For shield grounding, the resistance is generally 30 ohms.
For anti-static grounding, since the static current is very small (microampere level), the grounding resistance is approximately 100 ohms.
Therefore, the required grounding resistance value varies depending on the on-site environment, and the difficulty of grounding construction also differs accordingly.
Grounding Capacitance Value
When using capacitance for grounding, a method of DC floating ground and AC grounding is adopted. When the capacitance is fixed, the higher the frequency of the interference signal, the lower the impedance of the capacitor circuit. Capacitance grounding is effective in filtering out high-frequency interference signals. The capacitance value is generally 102/2KV.
The choice of grounding method needs to be determined based on the on-site environment. Instrument grounding is essential to ensure instrument safety, personnel safety, and the reliable operation of instruments.
Grounding Methods
There are two basic grounding methods: independent grounding systems and shared grounding systems.
1. Independent Grounding System
Grounding is achieved through dedicated grounding stakes or grounding objects (such as metal pipes). Independent grounding can meet the requirements of safety grounding, electromagnetic compatibility grounding, and lightning grounding. When using metal pipes for grounding, it is necessary to ensure the pipes are not floating and have a large contact area with the "earth" soil; otherwise, it cannot be considered reliable grounding.
2. Shared Grounding System
The grounding system of a building (reinforced concrete structure) is a shared grounding system, in which lightning protection, power supply, safety, and instrumentation share a single ground grid. It uses the building's steel structure, rooftop lightning protection devices, ground floor ground grid, floor-wise equipotential grids, and annular grounding busbars, etc., welded together to form an electrically connected cage-like grounding system, also known as a Faraday cage.
The grounding point of the instrument must maintain a sufficient safe distance from the lightning protection grounding point and should not be connected to the same grounding point to prevent lightning current from flowing into the instrument. Engineers can determine the grounding method based on on-site conditions.
