Same batchPCI-E to 4-port RS485/422 serial port card, some sites have been used for ten years without being disconnected, and some have reported verification errors every three days. The difference is often not in the card, but in the bus construction. If the following three points are implemented one by one, the link quality will be significantly improved.

Terminal resistor: 120 ohms only at both ends

The characteristic impedance of the RS485 cable is about 120 ohms. A terminal resistor should be connected to each physical end of the bus to suppress signal reflection. Parallel connection of the intermediate nodes will cause excessive bias and inability to drive the bus. It can be omitted in short distance and low speed, but as long as the speed reaches a higher level or the link spans more than 100 meters, the bit error rate of the bus lacking the terminal resistor will increase significantly.

Topology: hand in hand, rejecting stars and long branches

• The main trunk connects each node in sequence, and the branch drag lines are generally controlled within half a meter;
• Use twisted-pair shielded wires throughout the entire process, with A connected to A and B connected to B, with uniform polarity throughout the chain;
• The number of single bus nodes is left with a margin according to the driving capacity, typically 32, if more than that, add relays or segments.

Grounding and lightning protection: single-ended shielding

It is recommended that the shielding layer be grounded at one end. Grounding at both ends will form a ground loop, which is most likely to cause accidents during thunderstorms. In areas prone to lightning strikes and substations, in addition to installing surge protection, optical fibers can be used to electrically isolate the bus before entering the computer room. The idea of separating strong and weak currents isOptical isolation transformation of communication network in a 220kV substationIt has been verified in, similar requirements can be referred toCommunication transformation plan for electric power and new energy stations.

After the construction is completed, use a bus analyzer to spot-check the waveform and bit error rate, and archive the wiring routes to keep a base map for future capacity expansion. If you have any problems, please contact EB-LINK engineers for assistance in making judgments.