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  • Mb-gateway

    I'd like to extend a ethernet connection over long distance (wired) 1200 ft. Would it work if I installed a converter like this on each end? Basically what I want to do is convert ethernet to rs-485 and then back to ethernet. Speed is not a factor.

  • #2
    Maybe, maybe not. Depends what type of traffic you are trying to send over the Ethernet. You will probably only be able to send PLC type data (modbus), not normal computer traffic. It will also be VERY slow. The best you could hope for is around 0.1mb/s, and that may need to be lowered to around 0.02 or 0.01mb/s. I know you said speed isnt a concern, but Im not sure if you realized just how slow of serial modbus communication would be compared to what Ethernet normally runs so I figured I would mention it.

    The best way to do it would be to use a fiber optic Ethernet cable. That will be more reliable over a long run than copper, and is rated to run miles and miles without issue. AD sells converters that take an Ethernet packet running over copper with electrical signals, and convert that to the exact same Ethernet packet but just running through a fiber optic cable with light pulses, and vise versa. This maintains full Ethernet compatibility as the data isnt being changed in any way, the medium over which it is being sent is the only thing that changes. Both computer data and industrial Ethernet data will travel properly over these cables.
    Get whichever you need for the type of connector on the fiber optic cable you use:

    There are other types of connectors, but Automation Direct doesnt sell them.

    Note that I have never actually bought anything from that website I linked for the fiber optic cable. You can try buying from there, but I was just showing an example of the cable you would need.
    Last edited by MikeN; 11-14-2018, 02:03 PM.


    • #3
      Thanks for your response MikeN, that is a good idea, but the cable is already in place underground (Cat5).


      • #4
        So, you have cat5 (not even cat5e?) already run the whole distance of 1200ft? And you want to simply run an RS-485 modbus signal on that wire and convert it to Ethernet packets at both ends?

        I doubt that will work. Serial Modbus needs to have impedance set properly or reflections cause all sorts of communication problems. The issue gets worse the longer the distance is, and Ethernet cable does not have the proper impedance for modbus. If the distance was shorter, say 100-200ft, then it would probably work ok. But 1200ft? Thats asking for problems IMO.

        What was this cable used for in the past? Seems weird for an Ethernet cable to be run for that distance when copper Ethernet spec cannot even come close to supporting that.


        • #5
          Its intended purpose was for a phone system which is in place, but there are a couple of unused pairs available.........I guess a wireless bridge would be the most logical solution.


          • #6
            Originally posted by pbw View Post
            Its intended purpose was for a phone system which is in place, but there are a couple of unused pairs available.........I guess a wireless bridge would be the most logical solution.
            If you have line of sight that would be a great solution. You can use something like this to do what you need:

            Having half of the 4 pairs of wires available used for phones complicates this even more. That will further be a limiting factor for trying to use the wire as analog phone systems running through these wires have voltage ranging anywhere from 48 to 105 volts DC (usually closer to 48v). When a phone is ringing, 90 volts AC is also on the same lines. Cat 5 is not shielded and not optimized well for preventing crosstalk, so you will have some voltage bleed over from the wires running 1200ft parallel to each other. This will cause even more signal issues. Honestly any time a phone rings I would expect all your modbus communication through this cable to drop out from interference. I really dont think you should think about using this cable for anything else other than the phone system it currently runs. You either need to use the wireless option like you are thinking now, or run a new cable alongside this existing one. Preferably in fiber optic so the length isnt an issue and interference from the wire running next to it wont be an issue.
            Last edited by MikeN; 11-14-2018, 02:04 PM.


            • #7
              +1 for the NanoStations. We have several of them in the field for inter-PLC communications and have had no trouble out of them with the exception of one that moved out of place in a storm. I would not use them for I/O control, but for messaging between processors and even remote HMI they have been fine.


              • #8
                Thanks for your help, I will look into into it.


                • #9
                  There are also Ethernet range extenders that will work on copper for over a mile. Google "ethernet range extender" there are a lot of them out there. But we have used a lot of the Ubiquiti radios (NanoStations, Rockets, etc) and they work great if you have line of sight.

                  Last edited by jwbaker3; 11-13-2018, 10:22 AM.


                  • #10
                    I have an Ethernet to serial interface ( rs232/485), connected to a switch which exits to wifi via a range extender. Also the click Ethernet plc is tied to the switch. I connect from laptop to plc via wifi and the rs485 modbus devices I can access from plc over the interface.
                    i believe rs485 would work at 1000ft, you need to check the hardware specs.