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Modbus RS485 chain question

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Dgocof123
Dgocof123 Member Posts: 3
in THE MAIN WALL

We are setting up a system that has temperature control software to control a modulating gas valve through a Fuji temperature control unit and it has two wire RS485. We are creating a chain with three Invertek e3 VFD's that are 3 wire RS485. We feel we will have control issues with two wire and three wire communication in the same chain.

Two part question.

What are your thoughts and experience with this?

Second question, is there a work around like a usb hub combining two RS485 chains with slave 1-5 communicating on the same settings? Our software only allows communication to one rs485 usb chain on one com port with one usb plug.

Comments

  • ratio
    ratio Member Posts: 4,064

    I don't think you'll have any trouble with it, but you never know. There are rs-485 to Ethernet converters, a pair of those should isolate the segments at the cost of more complexity and additional cabling.

  • 109A_5
    109A_5 Member Posts: 2,480

    RS-485 is a three wire network and it can go thousands of feet if done right. Using it as 2 wire assumes a common ground is present that has no voltage offset between the two (or more) pieces of equipment. There are various ways to provide isolation if the ground is an issue.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Kaos
    Kaos Member Posts: 674

    Important bit is to use shielded twisted pair. The shield should only be grounded in one spot right at the PLC.

    Generally mobus RTU is pretty forgiving. If you have long run don't forget the termination.

    PC7060

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