Questions about 485 communication cables
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1. For the motor protectors in my distribution room, I use 485 communication; however, I employ network cables for the communication lines, and I have connected 12 motor protectors in series. I’ve used it for a few months, and sometimes there’s no connection. . . Sometimes it’s normal again. . I was mainly checking the current, so I didn’t pay too much attention to it. . . Now I need to run a 485 communication cable about 500 meters long, but my company only has 1.5-mm diameter computer cables with 2 conductors. . . There is no twisted pair. . . I’m not sure if there’s a problem. .
A dedicated twisted pair is not necessary, but a shielded cable should be used, keeping it away from power lines; 500 meters is no problem.
Shielded twisted pair can be used. But if the distance is long and there are many packet losses, the communication frequency needs to be reduced. See if you care about slow speed. My experience: 485 RTUs, loop length of 500 meters, 14 devices, standard 120/485 communication cables. Maximum speed of 19.2K, 2 packet losses, data refresh rate of about 2S. For 500 meters, it is recommended to use 485 cables, which are not too expensive.
Isn’t 485 just a twisted pair cable? Are there any dedicated cables as well?
This post was last edited by HEJIYUER on 2020-7-14 00:14. In digital communications, it is necessary for the characteristic impedance of the cable (not its resistance) to be matched with the terminal impedance. For example: in 485 RTU systems, the characteristic impedance of the cable signal lines is 120 ohms (for your application); in PROFIBUS-485 systems, it is 150 ohms. PROFIBUS -PA, cable signal line, characteristic impedance 120 ohms. The cable of FF-H1 is the same. In addition to impedance matching, the distributed capacitance of communication cables is also important, as it causes distortion in the communication square wave signals, leading to an increased error rate, packet loss, and even communication disruption. Twisted pair; I haven’t tested its characteristic impedance. However, the capacitance of 1.5mm2 cables is relatively high, and their performance does not meet the required standards; the distance they can be used over and the data transfer rate depend on the specific conditions at the site.