PROFINET to DeviceNet Gateway for Rockwell Drives in Desalination
Industrial Insight: Retrofitting legacy drives with modern PLCs using protocol gateways is a practical strategy for water treatment plants facing mixed-vendor control systems.
In a recent seawater desalination project at an industrial park in Shandong, engineers faced a classic integration challenge. The existing reverse osmosis membrane filtration line relied on four Rockwell PowerFlex 525 variable frequency drives to control high-pressure pumps. These drives communicated over a DeviceNet network. However, the new centralized control system was built around a Siemens S7-1200 PLC using PROFINET. The two protocols are incompatible, creating a communication barrier that threatened to delay the project and inflate costs.
Replacing all four drives with PROFINET-compatible models would have cost nearly six figures and extended the commissioning timeline beyond the plant’s startup deadline. Instead, the team deployed a protocol conversion gateway (model JH-PN-DVNM) to bridge the networks. This device acts as an intelligent translator between DeviceNet and PROFINET, enabling seamless data exchange without modifying the existing drives or PLC program structure.
How the Gateway Works
The gateway connects on one side to the Siemens PLC via standard Ethernet (PROFINET RT), and on the other side to the DeviceNet trunk line where the four drives are daisy-chained. Configuration involves mapping DeviceNet objects—such as speed reference, start/stop commands, and status feedback—to PROFINET I/O slots. These slots are then linked to data blocks in the TIA Portal project.
A critical step during commissioning was verifying the data mapping table. For instance, the “Run/Stop” control bit in the DeviceNet output assembly might be located at byte 2, bit 3. The gateway must ensure this bit is correctly placed in the PROFINET output data area so the PLC can control the drive reliably. Similarly, drive status bits, actual frequency, and fault codes are mapped to PROFINET input slots for monitoring.
The gateway handles protocol differences transparently. DeviceNet uses a polled I/O mechanism, while PROFINET relies on cyclic real-time communication. The gateway buffers drive data and synchronizes it with the PLC at a configurable update rate—in this case, 100 ms. This ensures consistent pressure control without overloading either network.
| Parameter | DeviceNet Object | PROFINET Slot | PLC Data Block |
|---|---|---|---|
| Speed Setpoint | Output Assembly, Byte 0-1 | Output Slot 1, Byte 0-1 | DB10.DBW0 |
| Run/Stop Command | Output Assembly, Byte 2, Bit 3 | Output Slot 1, Byte 2, Bit 3 | DB10.DBX2.3 |
| Actual Frequency | Input Assembly, Byte 0-1 | Input Slot 1, Byte 0-1 | DB10.DBW4 |
| Fault Code | Input Assembly, Byte 2 | Input Slot 1, Byte 2 | DB10.DBB6 |
After three months of continuous operation, the results were impressive. The gateway maintained zero communication interruptions, and the pressure control accuracy for the membrane feed pumps stayed within ±0.5% of the setpoint. The measured latency from the PLC issuing a speed command to the drive responding was under 15 ms, well within the real-time requirements for pressure regulation in reverse osmosis systems.
Key Benefits of the Gateway Approach
- Cost Savings: Retaining the existing drives and adding a single gateway saved approximately 70% compared to replacing all four drives with PROFINET-native models.
- Fast Response: The 15 ms control latency ensures tight pressure regulation, critical for membrane longevity and energy efficiency.
- Simplified Maintenance: PLC programmers work exclusively with PROFINET data blocks, while drive specialists continue using Rockwell software (e.g., Connected Components Workbench) for drive configuration and diagnostics—no cross-training needed.
- Scalability: The gateway can handle up to 63 DeviceNet nodes, allowing future expansion without additional hardware.
This project highlights a broader trend in industrial automation: protocol gateways are becoming essential tools for integrating legacy equipment into modern control systems. In water and wastewater facilities, where equipment lifecycles often span decades, such gateways enable step-by-step digitalization without massive capital expenditure. They also reduce risk by preserving proven field devices while upgrading the supervisory control layer.
When selecting a gateway for similar applications, engineers should consider several factors: the number of nodes supported, the maximum I/O data size per node, configuration software ease of use, and diagnostic capabilities. The gateway used in this project provided a web-based interface for real-time monitoring of both network sides, which proved invaluable during commissioning and troubleshooting.
Practical Tip: Always verify the endianness (byte order) when mapping multi-byte parameters like frequency or current. A mismatch can cause erratic drive behavior. Most gateways allow swapping byte order in the mapping configuration.
For system integrators and plant engineers facing similar multi-vendor challenges, the message is clear: protocol conversion gateways are not just “wiring boxes” but intelligent adaptation layers that resolve equipment lifecycle mismatches. They allow older but reliable devices to continue delivering value in modern, interconnected automation architectures. In an era where sustainability and cost-efficiency are paramount, such retrofit solutions are often more pragmatic than rip-and-replace strategies.
As industrial IoT and Industry 4.0 initiatives advance, the ability to integrate diverse fieldbuses and industrial Ethernet protocols will only grow in importance. Gateways that support multiple protocols—such as PROFINET, DeviceNet, EtherNet/IP, Modbus TCP, and PROFIBUS—are becoming standard components in the automation engineer’s toolkit, ensuring that no device gets left behind in the digital transformation journey.
