DeviceNet to Profibus DP Gateway for Siemens PLC Servo Control
In modern manufacturing, integrating legacy automation systems with new high-performance equipment often presents a significant challenge. A common scenario involves a Siemens PLC using Profibus DP needing to control a servo drive that only supports DeviceNet. Rather than replacing the entire control system—a costly and time-consuming endeavor—engineers can deploy a protocol conversion gateway. This article explores a real-world case where a DeviceNet to Profibus DP gateway enabled a brewery to increase production speed by 30% with zero downtime.
The Integration Challenge: Profibus DP Meets DeviceNet
A high-speed filling line at a brewery needed to upgrade its capping machine to meet increased demand. The existing setup used a Siemens S7-315-2DP PLC (6ES7 315-2AG10-0AB0) communicating via Profibus DP to control SEW inverters. While reliable, the system could not achieve the required speed. The engineering team selected an AB Ultra 3000i servo drive (2098-DSD-030-SE) with a built-in DeviceNet interface for its precise torque control and faster cycle time. However, the PLC and servo spoke different industrial protocols.
Replacing the PLC would have caused at least seven days of production stoppage, resulting in losses exceeding $800,000. The solution was to insert a DeviceNet to Profibus DP gateway, acting as a bridge between the two networks. This approach allowed the existing PLC to command the new servo without any hardware changes to the controller.
Key Takeaway: Protocol gateways enable phased modernization, preserving legacy investments while adopting advanced drives and devices.
Network Topology and Hardware Setup
The physical layout consisted of two distinct network segments:
- Profibus DP side: Standard 6XV1 830-0EH10 bus cable with active termination resistors (6ES7 972-0DA00-0AA0). The gateway was set as DP slave address 15.
- DeviceNet side: BELDEN 3082A armored shielded cable, 120 Ω termination resistors at both ends. The cable was routed at least 1.5 meters away from VFD lines to minimize noise. The gateway chassis was independently grounded to less than 4 Ω.
The gateway was mounted on a 35 mm DIN rail inside the control cabinet. Its built-in web server (default IP 192.168.1.6) provided real-time diagnostics, including DeviceNet scan list status and error counters.
Gateway Configuration Step by Step
Configuring the gateway involved three main stages: hardware initialization, PLC software setup, and data mapping.
1. Hardware Initialization
The gateway’s DIP switches set the Profibus DP slave address to 15 and the DeviceNet baud rate to 500 kbps. Using RSNetWorx for DeviceNet, the Ultra 3000i EDS file was imported, allowing automatic recognition of the servo’s I/O Assembly 20 (8 bytes input, 8 bytes output).
2. STEP 7 Hardware Configuration
In Siemens STEP 7 HW Config, the gateway’s GSD file (YC_DNTM_DP.GSD) was installed. The gateway was added as a DP slave, and 8 bytes of consistent input/output data were mapped to PIW256 and PQW256. Setting the data consistency to “Total Length” prevented byte-level splitting that could corrupt torque commands.
3. Data Mapping
The gateway transparently mapped the 8-byte output from the PLC to the DeviceNet assembly, controlling speed, torque, and enable signals. Input bytes reported actual position, torque feedback, and status. This mapping was pre-configured in the gateway firmware, requiring no custom scripting.
| PLC Output Byte | Function | PLC Input Byte | Function |
|---|---|---|---|
| Byte 0 | Control Word (Enable, Fault Reset) | Byte 0 | Status Word (Ready, Alarm) |
| Byte 1-2 | Torque Reference (16-bit) | Byte 1-2 | Torque Feedback (16-bit) |
| Byte 3-4 | Speed Reference (16-bit) | Byte 3-4 | Actual Speed (16-bit) |
| Byte 5-7 | Reserved / Configuration | Byte 5-7 | Fault Code / Diagnostics |
Commissioning and Performance Tuning
The commissioning process followed a segmented verification approach:
- First, the DeviceNet network was tested independently using RSNetWorx online scan, confirming node 12 communication quality above 98%.
- Then, the Profibus DP connection was activated. STEP 7 online monitoring showed zero errors in the DP diagnostic buffer.
To achieve the target throughput, the torque ramp rate was reduced from 200 ms to 80 ms, and the gateway’s internal scan cycle was shortened from 8 ms to 4 ms. These adjustments increased the capping speed from 1,200 bottles per hour to 1,560 bottles per hour—a 30% improvement.
A 72-hour continuous production test followed, processing over 21,000 bottles. There were zero communication interruptions, torque control accuracy remained within ±0.05 N·m, and the cap rejection rate dropped from 0.8‰ to 0.2‰, saving approximately $50,000 annually in material waste.
Reliability and Diagnostics
The gateway incorporated several features to ensure robust operation:
- Dual 24 VDC redundant power inputs prevented scanning interruptions from a single power supply failure.
- OB82 diagnostic interrupt in the PLC program monitored the gateway status. In case of a “Bus-Off” event, the PLC immediately stopped the machine and activated a warning beacon. The gateway could auto-recover within 3 seconds.
- Built-in SD card slot allowed logging of DeviceNet messages for up to 30 days, aiding in troubleshooting intermittent issues.
Scalability and Future Expansion
One of the gateway’s key advantages is its “zero-code” expansion capability. Adding a new DeviceNet device, such as a flow meter, only requires checking a box in the gateway’s web interface. No changes to the PLC hardware configuration or program are needed. This flexibility simplifies future line upgrades.
Cost Analysis: The total investment for the gateway and cables was approximately $800, compared to an estimated $200,000 for a full PLC replacement. The payback period was less than one week of production.
Best Practices for DeviceNet to Profibus DP Integration
Based on this successful implementation, consider the following guidelines:
- Always use consistent data mapping (“Total Length”) to avoid byte fragmentation.
- Physically separate network cables from power lines, especially VFD motor cables.
- Implement diagnostic interrupts in the PLC to detect gateway faults quickly.
- Test each network segment independently before full integration.
- Leverage the gateway’s web server for real-time monitoring and historical data logging.
Conclusion
A DeviceNet to Profibus DP gateway provides a cost-effective, low-risk method to integrate modern servo drives into existing Siemens PLC systems. In the brewery application, it enabled a 30% throughput increase, improved quality, and paid for itself almost immediately. This approach is replicable across many industries where brownfield upgrades require bridging different industrial Ethernet and fieldbus protocols.
