RS485 network with remote nodes

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Alex Benim

Does anyone have experience in low cost solutions for connecting multiple PLCs in RS485 network with consecutive gaps between the nodes exceeding EIA485 specification's 4000 ft for both star and token ring-like networks. Fiber is not an option. Thanks in advance. Alexander Benim
 
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Kipton Moravec

> Does anyone have experience in low cost solutions for connecting multiple PLCs in RS485 network with consecutive gaps between the nodes exceeding > EIA485 specification's 4000 ft for both star and token ring-like networks. Fiber is not an option. Depends on what you are doing. There are many ways to skin this cat. What are the distances? Are you saying that you have some number of of PLC's and each one is > 4000 feet away from each other? More than likely, you mean the whole network is greater than 4000 feet. The easiest thing is to hook them up with a repeater. This simple device sits at the end of the 4000 feet, and passes data unchanged to the next 4000 foot link. http://www.bb-elec.com/serial_long_distance/rs422_repeater_chart.asp B an B Electric has a lot of neat stuff, look at otherthings on the web. There are other simple ways to impliment a star type of network with a very little software and a single board PC with multiple RS-485 interfaces. I have one working now with three ports, with less than $500 of off-the-shelf hardware. Another option is to look at modems. Not Telephone modems but short-haul modems. http://www.patton.com/products/short_range.shtml The RS-485 protocal can probably go more than 4000 feet if you are willing to go slower, and make sure the line is terminated correctly. If 2400 baud is an option then try it, see if you can make it work. The other problem you will have in any case with a long wire line is electrical interfearance. That wire is a BIG antenna. It can pick up lots of energy from an elecrical storm, even if the lightning is a few miles away. This is often enough justification to go to fiber optics. If you want to send me more information about the specifications, and exact situation, let me know at [email protected] Kip
 
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I meant that the PLCs may be > 4000 ft apart from each other. I agree that with as long as the nodes are within 4000 ft - repeater will work fine. Thanks. Alexa Benim
 
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