PROFINET Wireless Communication: S7-1200 to ET 200SP via Industrial Bridge

In modern industrial environments, extending reliable communication across large distances and through physical barriers is a common challenge. A typical scenario involves a central Siemens S7-1200 PLC located in a main control room, while distributed I/O stations like the ET 200SP are placed hundreds or even thousands of meters away in separate production halls. When wired connections are impractical due to cost, terrain, or obstacles, a robust wireless solution becomes essential. This article explores how an industrial wireless bridge can establish a transparent PROFINET link between an S7-1200 and multiple ET 200SP modules over 3000 meters, even with walls and a tunnel in between.

The Challenge: Long Range, Obstacles, and Non-Line-of-Sight

The project involved a Siemens S7-1200 PLC installed in a central control room and several ET 200SP distributed I/O modules located in a production workshop 3000 meters away. The ET 200SP stations were responsible for monitoring motor speeds, temperatures, pressures, and other field signals, while also executing control commands from the PLC. The distance alone exceeded the range of standard Wi-Fi or Bluetooth solutions. Additionally, the signal path was obstructed by multiple concrete walls and a large tunnel (10m x 15m x 15m), creating a non-line-of-sight (NLOS) condition. Wired options like fiber optic cables were considered but rejected due to the high installation cost and complexity of crossing the tunnel and existing infrastructure.

Key requirements for the wireless link included:

• Stable, real-time PROFINET communication with minimal latency and jitter.
• Support for multiple ET 200SP nodes concurrently.
• High immunity to electromagnetic interference common in industrial settings.
• Easy configuration and reliable operation without frequent maintenance.

The Solution: Industrial Wireless Bridge for PROFINET

The selected device was an industrial-grade wireless bridge specifically designed for long-range, harsh environment applications. These bridges typically operate in the 5 GHz or 2.4 GHz bands, use high-gain directional antennas, and support advanced features like MIMO and proprietary protocols to ensure reliable data transmission. In this case, a pair of bridges was deployed: one connected to the S7-1200 via Ethernet, and the other connected to the ET 200SP network through an industrial switch.

The bridge’s key specifications that made it suitable:

These bridges are often used in pairs to create a transparent Layer 2 connection, meaning the PROFINET frames are forwarded without any modification. This is critical for real-time industrial protocols that rely on precise timing.

Network Topology and Configuration

The implementation followed a simple yet effective topology:

• Control Room Side: The S7-1200 PLC (e.g., CPU 1214C) was connected via its PROFINET interface to the LAN port of the first wireless bridge. This bridge was mounted high on a wall, with its directional antenna aimed toward the remote workshop.
• Remote Workshop Side: The second wireless bridge was installed with a clear view toward the control room. Its LAN port was connected to an industrial Ethernet switch (e.g., SCALANCE XB008), which then distributed the connection to multiple ET 200SP interface modules (IM 155-6 PN ST).
• Wireless Link: The two bridges established a dedicated point-to-point wireless link. They were configured with the same SSID, WPA2-AES encryption, and a fixed channel to avoid interference.

Configuration steps included:

1. Setting both bridges to “Bridge” mode (transparent forwarding).
2. Assigning static IP addresses in the same subnet for management, but ensuring the bridges do not perform routing.
3. Adjusting transmit power to the maximum allowed by regulations (typically 30 dBm).
4. Enabling features like “Distance Optimization” to adjust ACK timeout for the 3 km span.
5. Using spectrum analysis tools to select the cleanest channel.

In the TIA Portal project, the ET 200SP stations were configured as standard PROFINET devices on the same subnet as the PLC. No special wireless settings were needed because the bridge handled the physical layer transparently.

Performance and Results

After installation and fine-tuning, the wireless link achieved a signal strength of -65 dBm, which provided a stable connection with a data rate of 300 Mbps. The PROFINET cycle time was set to 2 ms, and the system operated without any communication losses or errors over a continuous 7-day test period. Data accuracy exceeded 99.95%, meeting the stringent requirements of industrial control.

The multiple ET 200SP modules (up to 10 in this setup) communicated concurrently without interference, thanks to the bridge’s high throughput and low latency. The solution eliminated the need for expensive fiber optic cabling and significantly reduced installation time from weeks to just a few days.

Key Benefits of Wireless PROFINET with Industrial Bridges

• Cost Savings: Avoids trenching, conduit, and fiber optic cable costs, especially over long distances or difficult terrain.
• Flexibility: Easy to relocate I/O stations as production layouts change without rewiring.
• Reliability: Modern industrial bridges offer features like automatic channel selection, error correction, and redundant power inputs.
• Scalability: Can connect multiple remote sites by adding more bridge pairs or using point-to-multipoint configurations.
• Rapid Deployment: Setup can be completed in hours, minimizing production downtime.

Considerations for Implementing Wireless PROFINET

While wireless bridges offer a compelling solution, several factors must be addressed:

• Line of Sight: Although bridges can penetrate some obstacles, a clear line of sight or minimal obstructions yields the best performance. Use site survey tools to assess path loss.
• Interference: Industrial environments may have many RF sources. Conduct a spectrum analysis and choose channels wisely. DFS channels can avoid radar interference but may cause brief interruptions if radar is detected.
• Security: Always enable WPA2-AES encryption and consider MAC address filtering or VLAN segmentation to isolate control traffic.
• PROFINET Requirements: Ensure the wireless link supports the required update time and jitter. For high-speed motion control, wireless may not be suitable, but for most process automation and discrete I/O, it works well.
• Environmental Factors: Temperature extremes, moisture, and vibration require industrial-grade hardware with appropriate IP ratings.

Conclusion

Using an industrial wireless bridge to connect a Siemens S7-1200 PLC to remote ET 200SP I/O modules over 3000 meters proved to be a reliable, cost-effective alternative to wired solutions. The transparent bridging technology preserved the real-time characteristics of PROFINET, while the robust hardware overcame physical obstacles and electromagnetic interference. This approach is highly recommended for applications in water treatment plants, mining conveyors, large warehouses, and any scenario where cabling is impractical. As wireless technology continues to advance, such solutions will become even more prevalent in industrial automation, enabling more flexible and efficient production systems.