DP to EtherNet/IP Gateway Design for Metallurgical Lines

Modern metallurgical plants demand seamless communication between legacy fieldbus systems and advanced Ethernet-based networks. When a mining and metallurgy group in Inner Mongolia upgraded its facilities with a new 320 t/h semi-autogenous grinding line, an 80 MVA smelting furnace, and a 1,250 mm hot rolling mill, the challenge was to integrate existing Siemens S7-300 PLCs (Profibus DP) with new Inovance AC800 PLCs (EtherNet/IP) without disrupting production. This article details the design and implementation of a protocol conversion gateway that achieved millisecond-level response, ensuring zero downtime and improved operational efficiency.

System Architecture and Device Inventory

The existing Profibus DP network was built around a Siemens CPU 315-2DP (firmware V3.3, station address 2) controlling distributed I/O modules: four ET200M stations (6ES7 153-1AA03-0XB0) with 16DI/16DO each, two SM334 analog modules (6ES7 334-0KE00-0AB0) for 8AI/4AO, and a BW500 belt scale integrator operating at 9.6 kbps. The bus employed shielded twisted-pair cable (6XV1 830-0EH10) with active termination resistors.

The new EtherNet/IP segment featured an Inovance AC800-EC11 controller programmed with TwinCAT 3.1, acting as a scanner. It managed six IS620N servo drives and three IS5600 remote I/O racks. Network infrastructure relied on Hirschmann OCTOPUS 8M-EEC managed switches with ring redundancy and QoS support.

At the heart of the integration was a dedicated protocol gateway configured as a Profibus DP slave (address 7) and an EtherNet/IP adapter (IP 192.168.1.20). The device, mounted on a 35 mm DIN rail with IP20 protection, consumed only 200 mA at 24 VDC and featured a separate RJ45 port for web-based configuration.

Data Mapping Strategy for Real-Time Control

To meet the demanding cycle times of a 50 Hz rolling mill, the gateway was configured to exchange 44 bytes of input data and 36 bytes of output data. The mapping covered three critical process areas:

The gateway utilized a dual-port RAM mechanism, allowing the Profibus and EtherNet/IP sides to exchange data every 2 ms. This resulted in an end-to-end network latency of less than 10 ms, well within the requirements for closed-loop control of the rolling mill.

Step-by-Step Implementation

Hardware Integration

After powering down the system, the gateway was added at the end of the Profibus segment with its station address set to 7 via DIP switches and termination enabled. The DP port was connected to the last ET200M using the same shielded cable type. On the Ethernet side, a CAT5e shielded cable linked the gateway’s P3 port to the Hirschmann switch, with IP parameters configured as 192.168.1.20/24. Power was supplied from a Siemens PS307 module, and the protective earth terminal was securely grounded to ensure noise immunity.

Software Configuration

For the Profibus side, the gateway’s GSD file (GSD_JM_DPEIP_V21.gsd) was imported into STEP 7 V5.6. A new slave with address 7 was inserted, and a universal module of 44 bytes input / 36 bytes output was placed in slot 1. After downloading the hardware configuration, the CPU showed no errors, and the SF/BF LEDs turned off.

On the EtherNet/IP side, the gateway’s web interface (default IP) was accessed. Under the “EIP Scanner” page, two Assembly instances were created: Input Assembly 101 (44 bytes) and Output Assembly 100 (36 bytes). The Request Packet Interval (RPI) was set to 4 ms with a timeout of 16 ms. The resulting EDS file (JM_DP_EIP.eds) was exported and imported into TwinCAT 3.1. A Generic EIP Device was added with the matching IP and assemblies. After scanning, the connection status showed “Run” with a steady green network LED.

Data Verification

Validation tests confirmed bidirectional transparency. Forcing output QB256 to 0x55 in STEP 7 immediately reflected in the corresponding TwinCAT input image. Writing a speed setpoint of 1.25 m/s from TwinCAT appeared as 1.25 (Real) in IW260 of the S7-300, with an error of only 0.01. A 24-hour burn-in test showed no station failures in the Profibus diagnostic buffer and zero packet loss on the EtherNet/IP connection.

Project Outcomes and Benefits

The integration was completed in just 28 days, achieving seamless data exchange between the Siemens Profibus and Inovance EtherNet/IP domains. Key results included:

• Interconnection of three major processes: 6 km underground belt conveyor, 80 MVA smelting furnace, and 1,250 mm rolling mill.
• Control response time consistently below 12 ms, meeting the 50 Hz dynamic closed-loop requirement.
• Production capacity increased by 6.7%, yield improved by 1.1%, generating an annual economic benefit of approximately 12 million yuan.
• No changes to existing PLC programs or field wiring, saving around 1.5 million yuan in retrofit costs.
• Provided a unified EtherNet/IP data interface for future integration with MES, energy management, and digital twin systems.

Key Considerations for Protocol Gateway Selection

When choosing a gateway for similar industrial automation projects, engineers should evaluate several factors:

This case demonstrates that with careful planning and the right protocol conversion technology, legacy fieldbus systems can be integrated into modern Ethernet-based control architectures without compromising performance or reliability. The approach not only preserves existing investments but also paves the way for Industry 4.0 initiatives.