There is dissimilarity and it is very vital to how your equipment operates. The Modbus/TCP and Modbus RTU over Ethernet will not be interoperable. More than expected, the Modbus RTU over Ethernet is a version wrapper of the protocol of Modbus RTU. This can be realized any one of a number of methods. The easiest way is to utilize a session of TCP/IP Telnet as the transport mechanism of Ethernet and Modbus RTU across the connection. This would be same to use serial tunneling presented by Lantronix, Z-world and other devices or software that transmit the characters in a characteristic serial link between two tools on a network of Ethernet with a session of Telnet.
The Modbus RTU was most likely created before the specifications of Modbus/TCP were available and was built to operate with a specific manufacturer’s implementation. You can also put in messages of Modbus RTU into frames of UDP/IP and basically transmit them onto the network. This is a easy process and runs well for networks that are basically a single segment.
Modbus/TCP is a specification built by Schneider Modicon to identify how the protocol of Modbus works and is covered on top of the TCP. The specification identifies the types of connection and basic structure of messaging. The function codes of application layer, responses, requests, etc. in Modbus/TCP are equal to those utilized in other systems of Modbus making it element of the family. Modbus/TCP also contains classes of conformance and in common tightens up the specification to assist assure interoperability.
One option that you may wish to think would use smart equipment like a processor of communications to save data from some PML meters at a time and make it accessible through a single port via a direct Ethernet connection or a serial tunnel. This would create the simpler configuration at the master of PI and harshly lessen overall communications on the network of Ethernet.