RS-485 communication via two wires?
RS-485 communication via two wires?
(OP)
We have an analog input module (Adam 4017) that needs to be connected to our data constrictor; they communicate via RS-485. The analog module has two pins (RS485+, RS485-) dedicated for communication.
Instead of buying RS-485 cable/converter to connect these two modules, I was wondering if I can just use two wires (say 16 gauge) to connect the two devices? I know ground shielding is needed, but I am testing it in a lab and the distance between the module is short (Practically next to each other). In an actual application I'd have a RS-485 cable.
Does anybody see any issue with using two wires here?
Thanks
Instead of buying RS-485 cable/converter to connect these two modules, I was wondering if I can just use two wires (say 16 gauge) to connect the two devices? I know ground shielding is needed, but I am testing it in a lab and the distance between the module is short (Practically next to each other). In an actual application I'd have a RS-485 cable.
Does anybody see any issue with using two wires here?
Thanks





RE: RS-485 communication via two wires?
RE: RS-485 communication via two wires?
TTFN
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RE: RS-485 communication via two wires?
RE: RS-485 communication via two wires?
If the module only has 2 terminals then it should be using earth ground as the common wire.
RE: RS-485 communication via two wires?
Keith Cress
kcress - http://www.flaminsystems.com
RE: RS-485 communication via two wires?
The OP did ask about the type of wire. Almost any type of wire would work for very short runs. The devices are likely connected to a common power source (like a power bar) so the devices using earth for the ground connection really shouldn't be an issue.
RE: RS-485 communication via two wires?
TTFN
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RE: RS-485 communication via two wires?
Keith Cress
kcress - http://www.flaminsystems.com
RE: RS-485 communication via two wires?
The FT-10 transceivers are transformer-isolated and very rugged.
Best to you,
Goober Dave
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RE: RS-485 communication via two wires?
Dave - good example of the wiring that will work but not good to compare no requirement for a common wire in that network to the common requirement of the RS-485 network.
RE: RS-485 communication via two wires?
TTFN
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RE: RS-485 communication via two wires?
AN0005
The part under grounding and partially isolated RS-422/485 is what we are talking about when you install an isolator and then still run a 2-wire network. As I already posted, it doesn't eliminate any of the grounding problems and just protects the port on the device. The grounding issues are just moved to the isolated port on the isolator.
RE: RS-485 communication via two wires?
TTFN
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RE: RS-485 communication via two wires?
RE: RS-485 communication via two wires?
1. The port is not isolated so you must only run 2-wires. The port is already using earth ground for the common of the RS-485 port so no further wiring is necessary.
2. The port is isolated and you decide to only run 2-wires. You must then connect the common of the RS-485 port to earth ground yourself.
3. The port is isolated and you run 3-wires, using the 3rd wire to tie the common of the RS-485 port to the common of the other RS-485 ports in the system. You must not connect the common of the RS-485 port to earth ground.
Norway2 - you need to do some reading on how RS-485 works.