Comprehensive Analysis of Siemens PLC Communication Protocols: How to Choose Between PROFIBUS, PROFINET, and Ethernet?
Hello everyone, I am Lao Chen. When it comes to industrial automation, PLC communication is undoubtedly one of the core skills. Especially when using Siemens PLCs, choosing the right communication protocol can save half the effort during on-site debugging. Today, let’s discuss PROFIBUS, PROFINET, and standard industrial Ethernet: what they are, suitable scenarios, how to choose, and common pitfalls encountered on-site.
1. What are the three protocols? Explained through everyday scenarios
1. PROFIBUS – The classic “old telephone line”
PROFIBUS is a fieldbus protocol that became popular in the 1990s, which can be understood as the “old telephone line in industrial automation.” It connects various devices with a single purple shielded twisted pair cable, allowing them to communicate in turn.
Application scenarios: Upgrading old factories, devices with high real-time requirements (such as servo motor control), and having hundreds or thousands of field input/output points.
Advantages and disadvantages:– Advantages: Strong anti-interference, good real-time performance, mature and stable– Disadvantages: Complex wiring, inconvenient expansion, difficult debugging
2. PROFINET – The modern “local area network”
PROFINET is essentially an industrial protocol based on Ethernet, which can be seen as an “industrial local area network.” It uses standard network cables, similar to connecting a computer to a home router.
Application scenarios: New production lines, device networking, and high-speed large data transmission needs, such as visual inspection and data collection.
Advantages and disadvantages:– Advantages: Simple wiring like network cables, fast speed, easy expansion– Disadvantages: High requirements for network environment, slightly weaker anti-interference capability than PROFIBUS
3. Ethernet – The “universal connector”
The Ethernet mentioned here refers more to TCP/IP standard communication, similar to how we use the internet on computers. PLCs, upper computers, databases, and cloud platforms all rely on it for interconnectivity.
Application scenarios: Remote data collection, integration with IT systems, and cloud platform connectivity.
Advantages and disadvantages:– Advantages: Strong universality, easy to connect with various systems– Disadvantages: Average real-time performance, susceptible to network fluctuations
2. Comparison of hardware wiring and configuration
1. PROFIBUS wiring diagram
[PLC]---[ProfibusDP Interface]---Purple Twisted Pair---[Inverter/Remote IO]Notes:– The wire ends must be tightly crimped!– Terminal resistors must be added at both ends; otherwise, communication will be unstable
2. PROFINET wiring diagram
[PLC]---RJ45 Network Cable---[Switch]---[IO Module/Inverter/Touch Screen]Notes:– It is recommended to use industrial-grade switches– Keep the on-site network cable length within 100 meters
3. Ethernet wiring diagram
[PLC]---RJ45 Network Cable---[Enterprise LAN]---[Upper Computer/Database]Notes:– Make sure to configure the router correctly so that the PLC can “find its home”
3. Communication settings ladder diagram/code examples
1. PROFIBUS configuration (using S7-300 as an example)
In the Step7 hardware configuration, right-click to insert the PROFIBUS DP slave and set the address.
Common faults:– Address conflict (different device addresses cannot be duplicated)– Terminal resistor not added
2. PROFINET configuration (using TIA Portal as an example)
- In the hardware configuration, drag and drop the device into the PROFINET segment.
- Set the IP address and device name.
- Download to the PLC.
Notes:– Device names must be unique; otherwise, communication will fail
3. Ethernet communication (S7-1200 as an example, TCP client)
// Communication block example (calling TCON, TSEND, etc. function blocks to implement TCP communication)Experience sharing:– Ensure that the IP address and port number do not conflict with the company network segment– Firewall settings must allow the relevant ports
4. Practical application cases
1. Classic PROFIBUS application
A mechanical factory’s old production line uses S7-300 + PROFIBUS to connect dozens of distributed remote IOs, demonstrating strong anti-interference capability, running smoothly for ten years without issues.
2. PROFINET practical case
A food factory’s new production line uses S7-1500 + PROFINET to connect visual inspection and robots, handling large data volumes at high speeds, and making equipment replacement easy.
3. Ethernet application
A logistics system uses S7-1200 to connect with the upper computer database via Ethernet, allowing production data to be uploaded to the cloud in real-time for convenient remote monitoring.
5. Common problems and solutions
- Communication failure?Most likely related to IP address, device name configuration, cable quality, or terminal resistors; focus on checking these.
- Occasional disconnections?Check power ground, grounding, and anti-static measures, especially near inverters.
- Mixing old and new devices?A gateway can be used to connect PROFIBUS and PROFINET; do not force compatibility.
6. Protocol selection recommendations
| Protocol | Recommended Scenarios | Speed/Real-time Performance | Ease of Use | Compatibility | Cost | Remarks |
|---|---|---|---|---|---|---|
| PROFIBUS | Old production lines/High real-time requirements | High | Average | Good | Higher | Strong anti-interference, complex wiring |
| PROFINET | New production lines/Modular expansion | High | Very good | Very good | Higher | Easy to expand, user-friendly debugging |
| Ethernet | Upper computer/Cloud platform integration | Average | Very good | Excellent | Low | Inexpensive, but average real-time performance |
Notes:– Before making a plan, communicate with on-site electrical engineers to avoid making arbitrary protocol selections– Prepare spare communication cables and ensure redundancy at critical nodes
7. Practical exercise recommendations
- Use two PLCs and one remote IO module to set up PROFIBUS and PROFINET communications, experiencing the differences in configuration and debugging
- Use a PLC and a computer for Ethernet communication, attempting to analyze data flow using Wireshark
- Intentionally disconnect terminal resistors and set incorrect IP addresses to observe alarms and error prompts, learning troubleshooting approaches
Final reminder: Choosing the right communication protocol can reduce on-site debugging efforts. Don’t shy away from the hassle; conduct more experiments and pay attention to error prompts. In technology, hands-on experience is often more reliable than just reading!