Hi experts,
I'm having some problems for choosing a right cable for a Modbus RTU (RS485) network. I know a should use a shielded twisted pair. But it can be any kind?
Kind Regards,
Mathew Lingdom
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Belden is usually the reference when it comes to cables. Check out this FAQ for cables. But the layout, grounding and termination are also critical. |
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You may find it depends heavily on the specific installation. I've seen the cheapest, non-shielded twisted pair wiring or even CAT5 cable (using one of the twisted pairs) in applications where there's not a bunch of interference flying around and things work flawlessly, even without a hint of the correct termination. I've also seen applications where the wiring is absolutely critical, including shielding and termination. Overall, RS-485 is a lot like CAN wiring... quite robust and tends to be difficult to get NOT to work despite some questionable wiring practices. |
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Actually you should use a shielded three way cable, like Belden 3106A. Why use this kind of cable? You don't want to get noise from ground loops on your network. Take a look on this article: http://www.chipkin.com/articles/rs485-cables-why-you-need-3-wires-for-2-two-wire-rs485 Kind regards. |
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