单点接地和 多点接地详解Single point grounding and multipoint grounding.docx

1、单点接地和 多点接地详解Single point grounding and multipoint grounding单点接地和 多点接地详解（Single point grounding and multipoint grounding）Single point earthing multi point earthingThe problem to be solved in a single point is the public ground impedance coupling and the low-frequency loop,More often than not, it is a

2、imed at common mode interference caused by long running linesIn low frequency circuits, the operating frequency of the signal is less than 1MHz, and its wiring and inductance between the devices are less affected, and the circulation caused by the grounding circuit has a greater impact on interferen

3、ce, so it should adopt one point grounding.When the signal operating frequency is greater than 10MHz, the ground impedance becomes very large. At this point, the ground impedance should be reduced as far as possible, and the ground multipoint grounding should be adopted.When the working frequency is

4、 between 1 and 10MHz, if one point grounding is adopted, the ground wire length shall not exceed 1/20 of the wavelength, or multipoint grounding method shall be adopted.Single point earthing between digital and analog ground, multipoint connection within digital ground.Ground wire interference and g

5、round wire designGround design is a problem that people pay attention to in EMC design, but they dont know how to do it. After understanding the mechanism of the interference caused by ground wire, there is a definite idea in the design and implementation of ground wire. This issue begins with the i

6、ntroduction of the principle of interference caused by ground wire, enabling readers to understand the key and principles of designing ground wire. 1 what is the earth wire?There are two kinds of ground wire: safety and signal. The former is to ensure personal safety and equipment safety and set the

7、 ground wire, the latter is to ensure that the circuit works correctly set the ground wire. The main reason for the circuit interference is the signal ground, so the problem of signal ground is only discussed here.The general definition of the signal field is the potential reference point of the cir

8、cuit.More appropriately, this definition is a hypothesis in our design of circuits. From this definition it is impossible to analyze and understand some ground interference problems. From now on, we will use the following definition when we analyze electromagnetic compatibility problems.The ground l

9、ine is the ground impedance path of the signal current flowing back to the signal source.Since the ground wire is a path of the current, then there is a voltage on the ground line according to Ohms law; since the earth is on a voltage, the earth line is not a equipotential body. In this way, when we

10、 design the circuit, the hypothesis about the potential of the ground wire is no longer established, so there are various errors in the circuit. This is the essence of ground interference.How big is the impedance of the 2 wire?An incomprehensible problem is that when we design the ground wire, the r

11、esistance of the ground wire is very small, then the potential difference on the ground will be large enough to cause the level of circuit errors. To understand the problem, understand the composition of ground impedance.The ground impedance of Z by the resistance and inductance part is composed of

12、two parts, namely: Z = RAC + L J.Resistance component: the resistance of the conductor is divided into DC resistance RDC and AC resistance RAC. For AC current, because of the skin effect, the current is concentrated on the surface of the conductor, resulting in the decrease of the actual current cro

13、ss section, the increase of resistance, and the relationship between the DC resistance and the AC resistance:RAC= 0.076rf1/2RDCType 1: the radius of the r= wire, the unit cm, the current frequency of the f= flowing through the wire, the unit Hz, the direct resistance of the RDC= wire, the unit omega

14、.Inductance: any conductor has an internal inductance (which is distinguished from the usual external inductance,The outer inductance is a function of the area enclosed by the conductor, and the inductance is independent of the area enclosed by the conductor. For round sections, conductors are as fo

15、llows:L=0.2Sln (4.5/d) -1 (H)Type S= conductor length (m), d= conductor diameter (m)Table 1 illustrates the great difference between the DC and AC impedances. The impedance of very low frequencies can be considered to be the resistance of a conductor, can be seen from the table, with the increase of

16、 frequency, the impedance increases quickly when the frequency is above 100MHz, there are dozens of diameter 6.5mm ohm impedance of the wire length is only 10cm.Interference of 3 loop road and CountermeasuresLoop interference is a common interference that occurs between devices that are longer apart by longer cables. The intrinsic reason is the ground potential difference between the equipment. Ground voltage leads to the earth l