Grounding is a wire connection set to discharge charge or provide a reference potential. There are two purposes of grounding. One is to protect people and equipment from lightning, electric leakage, static electricity and other hazards. This kind of ground wire is called protective ground wire, which should be connected with the real earth. Second, to ensure the normal operation of the equipment, it is called the working ground wire.
1. Suspended ground
A. The ground wire of the equipment is electrically insulated from the reference ground and other conductors, that is, the equipment is suspended;
B. In order to prevent the disturbance current on the chassis from being directly coupled to the signal circuit, it is intentionally isolated from the chassis, that is, the suspended ground of the unit circuit.
2. Single point grounding
Single point grounding is to provide a common reference point for many circuits connected together. Parallel single point grounding is the simplest. It has no problems of common impedance coupling and low-frequency ground loop, so there is no disturbance.
3. Multipoint grounding
Multipoint grounding can avoid the problem of single point grounding at high frequency. Multipoint grounding must be used in digital circuits and high-frequency large signal circuits. Modules and circuits pass through many short wires (<0.1 λ) Connected to reduce the common mode voltage generated by the ground impedance.
4. Hybrid grounding
Hybrid grounding includes both single point grounding and multi-point grounding. For example, the power supply in the system needs single point grounding, while the RF part needs multi-point grounding. Hybrid grounding uses electrical resistance devices to make the grounding system show different characteristics at low frequency and high frequency, which is necessary in broadband sensitive circuits.
To sum up, mixed grounding shall be considered for the grounding of shielding machine room.