RS 485 isolator


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  1. #1
    Prolific Poster shantanu@india's Avatar
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    Default RS 485 isolator

    Hi,
    I have a situation where 10 to 12 RS-485 enabled devices are communicating to a remote SCADA through a 2-wire network.
    I need to provide electrical isolation modules at every node-point to avoid ground loops.
    Are any such devices available at reasonable prices or do I need to design my own isolator using high speed opto's?
    Thanks.
    Shantanu

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    Senior Member Ken_K's Avatar
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    Default Re: RS 485 isolator

    Hi Shantanu I do not know what is available so I cannot help with your question. If you have to make your own isolator I would look at digital isolators as they now seem to outperform opto's in most respects, some isolators are made specifically for RS485. It might pay to try a Digi-key search for Digital Isolators selecting RS485 in the parametric search. I have a hunch if you want a lot of these isolators making your own may be the cheapest option.

    Keep well
    Ken K

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    Prolific Poster shantanu@india's Avatar
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    Default Re: RS 485 isolator

    Thanks Ken.
    Yeah , I have used 6N136/137 opto's for isolating 9600 baud communication before......but for that I need dual power supplies on both the sides.
    Also I need to have a microcontroller for changing the direction for communication.
    I shall have a look at the digital isolators.
    Norm posted some links a few months ago....
    Shantanu

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    Prolific Poster RGV250's Avatar
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    Default Re: RS 485 isolator

    Hi,
    https://buy.advantech-bb.com/Serial/...l-BB-485OP.htm
    Not cheap but all depends on your time, I am sure there are others.

    Regards,
    Bob

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    Prolific Poster rcurl's Avatar
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    Default Re: RS 485 isolator

    Hi Shantanu-
    Do you need something that can be connected to the RS485 buss outside the units, or do you want something that you can add to a PCB you are designing? If you want an isolated transceiver you can add to your design, look at an Analog Devices ADM2483. If you need a bolt-on solution look here: https://www.ebay.com/itm/Isolated-RS...AAAOSw-cVdXVfc

    -Rick

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    Prolific Poster shantanu@india's Avatar
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    Default Re: RS 485 isolator

    Yes....costly!!
    My slave devices talk to the SCADA with fixed packet width of 24 bytes @ 9600 baud.
    Therefore , ideally any PIC with hardware UART & two SN75176 RS485 transceivers should do the trick....
    Of course digital isolators & dual power supply would be required for galvanic isolation.
    Shantanu

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    Prolific Poster shantanu@india's Avatar
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    Default Re: RS 485 isolator

    Quote Originally Posted by rcurl View Post
    Hi Shantanu-
    Do you need something that can be connected to the RS485 buss outside the units, or do you want something that you can add to a PCB you are designing? If you want an isolated transceiver you can add to your design, look at an Analog Devices ADM2483. If you need a bolt-on solution look here: https://www.ebay.com/itm/Isolated-RS...AAAOSw-cVdXVfc

    -Rick
    Hi Rick,
    Actually I am using PLC's for industrial weighing system connected in daisy chain fashion to the system PC running the SCADA software.
    The PLC 485-interfaces are non-isolated & apart from the D+ & D- terminals, have a ground terminal that is connected to the PLC motherboard ground. The manufacturer suggests to connect all the ground terminals also to eliminate common mode voltages. But without electrical isolation , connecting the ground terminals together is asking for trouble since it effectively connects all the PLC grounds to each other.
    Shantanu

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    Junior Member Giuseppe's Avatar
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    Default Re: RS 485 isolator

    It could be a starting point.

    https://www.massarielectronics.it/elettronica/5-progetti/22-scheda-interfaccia-massabus.html



    Instead of the Max232 put another MAX 485. Also remove FC3

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    Senior Member GAMBOA's Avatar
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    Default Re: RS 485 isolator

    Hi Shantanu,
    The solution that I implemented for some of my devices.

    Regards,
    Gamboa
    Attached Files Attached Files

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