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I. Key Points in Selecting RS485 Communication Cables
Characteristic Impedance Matching
RS485 communication requires that the characteristic impedance of the cable matches the port impedance of the communication equipment. Generally, the standard characteristic impedance is 120Ω. Using a dedicated RS485 communication cable with a characteristic impedance of 120Ω can minimize signal reflection and ensure the integrity of the signal during transmission. It's like choosing the most suitable baton for a relay race. Only when the size and weight are appropriate can the relay process go smoothly and avoid accidents.
Good Shielding Performance
There is often a large amount of electromagnetic interference in the industrial environment, such as the electromagnetic noise generated by motors and frequency converters. Therefore, RS485 communication cables must have good shielding performance. Cables with a metal braided mesh or aluminum foil shielding layer can effectively resist external electromagnetic interference, just like putting a strong "protective suit" on the communication signal, allowing it to be transmitted "unscathed" in a complex electromagnetic environment.
Wire Diameter Adapted to Transmission Distance
The wire diameter of the cable should be reasonably selected according to the transmission distance. For longer transmission distances (exceeding several hundred meters), a thicker wire diameter should be used to reduce signal attenuation. For example, at a transmission distance of about a kilometer, a wire diameter of 1.0mm² or thicker may be required to ensure that the signal strength can still meet the communication requirements during long-distance transmission. This is like choosing a stronger and larger-capacity transportation vehicle for long-distance transportation to ensure the complete transportation of goods (signals).

II. Connection Specifications for RS485 Communication Cables
Wiring Rules
 Keep Away from Interference Sources as Much as Possible: When wiring, the RS485 communication cable should be kept as far away as possible from strong electrical lines, large motors, frequency converters, and other interference sources. If crossing cannot be avoided, a 90° right-angle cross should be maintained to reduce the coupling of electromagnetic interference. This is like vehicles in different directions (signals and interference sources) on the road each following their own path to avoid collisions (interference).
 Adopt Bus Topology: The RS485 network is recommended to adopt a bus topology, that is, all devices are connected in parallel to the two buses, connected one by one like stringing beads. Avoid other complex topologies such as branches, rings, or stars to ensure the stability and consistency of signal transmission on the bus.
Setting of Terminal Matching Resistors
Terminal matching resistors need to be connected at both ends of the RS485 bus, and their resistance value is generally 120Ω, matching the characteristic impedance of the cable. The function of the terminal matching resistor is to absorb signal reflections and enable the signal to be transmitted stably on the bus. If the terminal matching resistor is not connected or the resistance value does not match, it may lead to the superposition of signal reflections, causing signal distortion and even communication failure. It's like in an echo wall, if there is no suitable sound-absorbing material (terminal matching resistor), the sound (signal) will keep reflecting and become noisy and chaotic.
Precautions for Cable Connections
 Solid and Reliable Connections: The connection between the RS485 cable and the equipment must be solid to avoid looseness or poor contact. Ways such as tightening with screws or welding can be used to ensure the reliability of the connection. Otherwise, the signal quality may be affected due to excessive contact resistance.
Avoid Cable Damage: During installation and use, care should be taken to protect the cable and avoid it being scratched by sharp objects, squeezed, or excessively bent. Any damage to the cable may lead to signal short circuit or open circuit and disrupt the entire RS485 communication link.
Shield Grounding Requirements
 Single-point Grounding Principle: The shielding mesh of the RS485 communication cable should follow the single-point grounding principle. Usually, the shielding mesh is grounded at one end of the RS485 bus, which can effectively prevent the generation of ground loop currents. Ground loop currents may introduce additional noise interference and affect the stability of RS485 communication. It's like in a circuit, we need to avoid forming unnecessary current loops to prevent interference.
 Reliable Grounding: The grounding connection should be reliable. Generally, it should be connected to the dedicated grounding terminal of the equipment or a metal cabinet with good grounding. The grounding resistance should meet the relevant standard requirements, usually requiring the grounding resistance to be less than 4Ω. Reliable grounding is like building a stable "reference potential" for the entire RS485 communication system, providing a stable reference for the signal during transmission and thus improving the quality and stability of communication.
Correctly selecting and standardly connecting RS485 communication cables is the foundation for building a stable and reliable RS485 communication network. Only by strictly following these principles can RS485 communication play its powerful role in fields such as industrial control and ensure efficient communication between various devices.