Connecting Modbus sensors using "RS485 to USB adapter"

Physical description

"USB485 / Modbus RS485 to USB adapter" is used for connecting Modbus RTU devices/meters/sensors to Vutlan VT325, VT335, VT805, VT825, VT900, VT960 series monitoring units.

Connection

Please read article Connecting Modbus devices first.

Example 1: Using "RS485 to USB adapter" with internal termination.

  • Sensors are connected in a daisy chain connection.
  • 120Ω resistor is used at the end of the chain.
  • Twisted pair cable is used for A(+) and B(-).
  • "RS-485 to USB adapter" has an internal termination and it is switched ON.
  • The data is transferred to Vutlan monitoring unit using USB port.
  • Up to 31 devices can be used.
  • Overall cable length no more than 1000 meters.

Example 2: Using "RS485 to USB adapter" withiout internal termination.

  • The same as the first example with the exception that the "RS-485 to USB adapter" does not have a built in termination.
  • T ermination (120Ω resistor) is added at the start of the chain.