Do you know how to design the system ground?
Grounding is the most effective way to suppress sources of disturbance and solve 50% of EMC problems. The system ground is connected to the ground to suppress electromagnetic disturbances. The metal parts of the case are directly connected to the ground, and can also provide an electrostatic charge leakage path to prevent static electricity from accumulating.
1, the concept of ground wire
Safety grounding: including protective earthing and lightning protection grounding.
Protective grounding: Provides a low impedance path for the product's fault current to enter the earth;
Lightning protection grounding: providing a path for discharging amplified current;
Reference Grounding: Provides a reference level for stable and reliable operation of the product, providing a reference potential for the power supply and signal.
The safety grounding is to provide a bleed circuit for high current and high voltage when some electrical anomalies occur, mainly as a protection measure for the circuit. The reference ground is mainly the signal ground and the power ground, which is the basis for ensuring the function of the circuit.
2, grounding method
Suspension grounding: There is generally no problem with a separate system with no external interface, but if the system has interfaces such as communication ports and sampling lines with other systems, then the floating ground is susceptible to static electricity and lightning strikes. The impact, so most of the general electronic products do not use floating grounding.
Single point grounding: When f<1MHz, single point grounding can be selected, which can be divided into parallel single point grounding and multi-stage circuit series single point grounding.
Parallel single-point grounding: Each circuit module is connected to a single point ground, and each unit is connected to the reference point at the same point.
Series single-point grounding of multi-stage circuits: Ground the circuits of similar characteristics to form a common point, and then connect each common point to a single point.
Multi-point grounding: Multi-point grounding is used when f>10MHz. The circuits in the device are all close to the ground bus as a reference point.
Single-point grounding circuits are connected at the same point, providing a common potential reference point, without common impedance coupling and low frequency ground loops, but with large ground impedance for high frequency signals. Multi-point grounding is grounded nearby, and each ground wire can be short and provides a lower ground impedance. 1MHz~10MHz can choose which grounding method to use according to actual needs.
Hybrid grounding: It is the advantage of integrated single-point grounding and multi-point grounding. It uses single-point grounding for the low-frequency part of the system and multi-point grounding for the high-frequency part of the system.
Signal line shield grounding There are high frequency and low frequency points, high frequency adopts multi-point grounding, and low frequency cable adopts single point grounding. The low-frequency electric field shielding requires a single point grounding at the receiving end, and the low-frequency magnetic field shielding is required to be grounded at both ends. Multi-point grounding, except grounded at both ends, and grounded at 3/20 or 1/10 operating wavelength intervals.
The system can be well grounded to effectively suppress electromagnetic interference. A large system cabinet must first ensure good contact with each surface and compact contact. Secondly, the internal equipment of the cabinet should be grounded nearby to avoid secondary interference and discharge electromagnetic interference. The interface shielded cable should be looped and then connected to the rack. A grounding copper bar is arranged under the cabinet. The copper strip is better for the system ground wire, and the electromagnetic interference is well discharged to ensure the normal operation of the system.
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