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Sunday, May 27, 2018
The OPC Community Forum.
RS485 to IP Converter
The difference between RS485 to IP converter and MODBUS RS485 to MODBUS TCP/IP gatway

What is the difference between RS485 to IP converter and MODBUS RS485 to MODBUS TCP/IP gateway? And how to know which converter support MODBUS not just regular converter? Because I want to send data from remote site with my WAN network and read it with OPC server software which support MODBUS TCP in SCADA site.

An I/P (eye to P) is a current(I)-to-pressure(P) transducer.

If the input side of the transducer is Modbus/RTU over RS-485, then don't you need a Modbus/P transducer; a Modbus pneumatic transducer? (in the absence of I, typically a 4-20mA current loop signal)

There are tens of thousands of devices that use proprietary protocols over RS-485, which is merely an electrical bus for communications. For example, Profibus DP.

If the device's spec does not say Modbus, then it doesn't use the Modbus protocol. Modbus/RTU is the serial version of Modbus, which could run over either RS-232 or RS-485 or both.

Good luck finding a commercial Modbus/RTU/485/pressure transducer. Valtek has Modbus/RTU (RS-485) valve positioner, or at least one is listed on the site.

Take a look at the Anybus Communicator - Modbus TCP (AB7072). This Communicator is capable of converting almost any type of serial protocol such as Modbus RTU, ASCII, DF1 or any other type of proprietary Query/Response or Produce/Consume protocol.

By Fred Loveless on 1 May, 2018 - 9:54 am

Greetings, it is actually very straight forward. An RS485 to IP/Ethernet converter Encapsulates the Serial packet in an Ethernet packet. The data Payload is still the Modbus RTU packet. Sometimes this is referred to as Modbus over TCP.

A Modbus RTU to Modbus TCP gateway is different. It takes the RTU packet, strips of the Checksum at the end and adds an MBAP header (Modbus TCP) at the beginning.

With converters you can only have one master device polling the RTU(s) but with a Gateway you can have more than one master polling the RTU devices through it. For Gateways, the number of masters depends on what it allows for simultaneous connections.