Y-Link Profibus Diagnosis in the Paper Industry


Our client, a leader in the paper production sector, is recognized for utilizing advanced technology and eco-friendly practices. Their plant uses 100% wastepaper in production, saving 10 million trees annually. Equipped with a $35 million treatment system, they are committed to environmental sustainability. The plant’s machinery consists of valves and sensors connected to modules such as IO racks, interface modules, and HMIs. PROFIBUS serves as the digital fieldbus data communication network that links these components.


The primary issue faced was an unstable Y-link network that caused frequent production line stoppages due to sudden network load increases. This instability forced frequent switches from auto mode to manual mode, significantly impacting production efficiency. The exact cause of these failures was unclear, making a comprehensive network diagnostic health check necessary.

After a thorough analysis, several problems were identified:

  • Improper installation and connection
  • Incorrect termination
  • Deviation from the standard Profibus installation practice of maintaining a one-meter distance from high voltage power lines

The main challenges included:

  • Reducing downtime caused by Y-link node failures
  • Stabilizing the Y-link network and balancing its load
  • Addressing low voltage issues and ensuring network redundancy
  • Facilitating network scaling for future expansions


We employed Profibus diagnostic tool kits, repeaters, terminators, connectors, cables, and a multimeter, along with a Simo code device configurator.

Proposed Solution

We connected the PROFIBUS diagnostic tool to each Y-link in the network to identify problems instantly:

  1. Y-link Errors
    • Using a Siemens S7-400 PLC with 24 master redundant Y-link branches, we tested each branch and found improper connections and termination issues causing System Faults (SF) and Bus Faults (BF1 & BF2). These were rectified by correcting connections and reprogramming the respective devices.
  2. Network Error Messages
    • The diagnostic tool detected illegal responses and repeated messages. We resolved these by updating the programs of the affected devices.
  3. Low Voltage Issues
    • To address low voltage levels, we added repeaters to ensure adequate voltage throughout the network.
  4. Network Load Imbalance
    • We discovered an unbalanced load on the PLC-S7400 due to uneven Y-link node distribution. By redistributing the nodes, we balanced the network load.
  5. Simo Code Program Errors
    • Persistent network problems were tackled by uploading new programs and replacing faulty Simo code cards.


After implementing these solutions, the Y-link network was observed for two days. No issues were found, confirming the network’s stabilization.


Our intervention restored the machine to 100% capacity, crucial for meeting tight delivery schedules. We provided a comprehensive comparison report of the network’s status before and after troubleshooting. Additionally, we offered Profibus training and guidelines for future troubleshooting.

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