EtherCAT to DeviceNet Gateway for Plastic Thermoforming Control
In plastic thermoforming production, precise coordination between material feeding and heating stages is critical for product quality. A recent project involved a Beckhoff PLC as the master controller, communicating via EtherCAT, while the heating oven used multiple temperature controllers with a DeviceNet interface. The challenge was to bridge these two incompatible industrial networks without replacing existing hardware or adding costly master modules.
The Protocol Gap: EtherCAT vs. DeviceNet
EtherCAT is a high-performance real-time Ethernet protocol with cycle times down to microseconds, ideal for motion control and fast I/O. DeviceNet, based on CAN bus, operates at a maximum of 500 kbps and is common in simple devices like temperature controllers, valves, and sensors. These two protocols differ at every level—physical, data link, and application—making direct communication impossible.
Replacing each temperature controller with an EtherCAT-compatible model would cost over $300 per unit. Adding a DeviceNet master module to the PLC rack would require managing two separate network stacks in the program, increasing complexity. A protocol conversion gateway offered a more elegant and cost-effective solution.
How the EtherCAT to DeviceNet Gateway Works
The gateway acts as a bridge with three core functions:
1. Protocol Conversion
The gateway appears as an EtherCAT slave to the PLC and as a DeviceNet master to the temperature controllers. It receives EtherCAT frames, extracts process data, and repackages it into DeviceNet messages (explicit or I/O). The PLC programmer only needs to read/write predefined memory addresses; the gateway handles all DeviceNet communication details transparently.
2. Data Mapping and Buffering
In this application, the heating oven had 8 temperature zones. For each zone, the PLC needed to read actual temperature, write setpoint, and monitor alarm status. The gateway maintains a mapping table that links EtherCAT cyclic process data objects to DeviceNet parameters. It also buffers the latest values, so if the DeviceNet network experiences a brief interruption, the PLC still gets valid data, preventing control disruption.
3. Electrical Isolation and Protection
EtherCAT uses standard Ethernet physical layer (100BASE-TX), while DeviceNet uses CAN transceivers with different voltage levels and common-mode ranges. The gateway provides galvanic isolation between the two networks, protecting the PLC from field noise and faults. If a temperature controller fails and shorts the DeviceNet bus, the gateway can isolate that port, keeping the rest of the system operational.
Performance and Results
After commissioning, the system achieved temperature control accuracy of ±1°C, significantly improving sheet heating uniformity. The gateway’s processing latency was approximately 2 ms, well within the thermal process response requirements.
| Parameter | Value |
|---|---|
| Temperature control accuracy | ±1°C |
| Gateway latency | ~2 ms |
| Cost savings vs. replacing controllers | ~60% |
| PLC program simplification | 40% reduction |
| Commissioning time reduction | 3 days |
Why Choose a Protocol Gateway for Retrofits?
In many industrial automation upgrades, equipment from different vendors and eras must coexist. Replacing all devices to match a single network standard is often prohibitively expensive. A protocol gateway offers a middle path:
- Preserve existing investment: Keep proven field devices and wiring.
- Simplify integration: The PLC sees a unified data interface.
- Enhance reliability: Isolation and buffering protect the control system.
- Reduce engineering time: No need to learn multiple network protocols in depth.
Key Considerations for EtherCAT to DeviceNet Gateway Selection
When selecting a gateway for similar applications, consider the following:
| Feature | Importance |
|---|---|
| EtherCAT slave stack conformance | Ensures compatibility with TwinCAT and other masters |
| DeviceNet master capability | Supports UCMM, explicit messaging, and I/O connections |
| Data mapping flexibility | Configurable mapping between cyclic data and DeviceNet objects |
| Isolation voltage | Typically 1500 VDC or higher for industrial environments |
| Configuration tool | User-friendly software for setting up mappings and DeviceNet scan lists |
Conclusion
The EtherCAT to DeviceNet gateway proved to be a reliable and cost-effective solution for integrating legacy temperature controllers into a modern EtherCAT-based control system. By handling protocol conversion, data mapping, and electrical isolation, it enabled precise temperature control without the need for hardware replacement or complex PLC programming. For any retrofit project involving mixed industrial networks, a well-chosen protocol gateway can deliver significant savings and performance improvements.
