Case Studies

Redundant DNP3 Communication Using a Siemens S7 PLC

Posted in Energy and Utilities, Manufacturing Automation and Intelligence, PLC Programming, Siemens PLC


DMC provided software to be loaded onto a network of S7-300 PLCs to send and recieve data to and from train system substations. This data was transmitted using DNP3, a robust and redundant TCP/IP communication protocol.

DNP3 Visual Overview


The customer needed to communicate important substation information using DNP3. All of the substations that needed to communicate over TCP/IP with the central SCADA system were already equipped with Siemens S7-300 PLCs and attached Ethernet modules that were being used to gather the information from the power substation. DMC used hardware already in place to provide functionality for all of the layers of the robust DNP3 protocol, and went to a train substation to verify and debug the system. 

The software DMC created used two separate Ethernet connections to communicate with the central server, thus helping prevent loss of data. Additionally the implementation had a large data buffer, so that even if both connections were down data would be sent after a connection was reestablished. Using the DMC software the server is able to send trip/close commands to relays, control analog setpoints, read digital outputs, and read analog values from any of the power substations in the network. This provided a stable communication system for the railroad's SCADA system.

Learn more about DMC's Siemens S7 PLC programming services.

Customer Benefits

  • Prevented expensive hardware upgrades to communicate using DNP3
  • Provided multiple connections and message handshakes that guaranteed delivery of information
  • Able to install on both future stations and all existing stations


  • DNP3 Communication Protocol
  • Siemens S7-300 PLC
  • Siemens CP343 Ethernet Module
  • Simantic Manager and Step 7 (Ladder, SCL, STL)
  • SCADA Newtork