PROFIBUS: 3 Sins and 10 Tips

The PROFIBUS industrial bus is highly tolerant and will forgive many faults. But if a critical fault occurs—or several small ones accumulate—you will definitely notice. That’s why this aging industrial network deserves attention. Even if faults on your network are still rare, they will gradually accumulate. What do our technicians recommend? What are their 10 tips for maintaining PROFIBUS?

FOXON technicians have performed hundreds of network diagnostics not only in manufacturing but also on bridge cranes, mining equipment, and in quarries. Often, they can immediately spot the root cause just by looking inside a control cabinet. However, they don't rely solely on their eyes—they use a diagnostic tool: the PROFITRACE analysis software. Before taking measurements and analyzing oscilloscope waveforms, they always start with a visual inspection. What do they look for?

PROFIBUS at First Glance

• Termination Resistors
  Termination resistors must be activated at both ends of a PROFIBUS network to prevent signal reflections. If not, communication failures will occur. Whether a termination resistor is on or off is usually obvious, so checking their status is the first thing technicians do during a visual inspection.

• PROFIBUS Proximity to Power Cables
  In industrial environments, it pays to follow standards and keep a safe distance between communication and power cables. Signal interference can distort communication, and shielding alone cannot prevent noise from induction. In practice, moving a PROFIBUS cable just 10 cm away from power cables can improve the signal margin by up to 15%!

Example from Practice: PROFIBUS Cable Running Close to Power Cables

• Cable and Connector Condition
  Damaged connectors, broken cables, or oxidized contacts can significantly deteriorate signal quality. If your equipment vibrates and is connected with stranded wire, avoid using IDC (insulation displacement) connectors. The vibrations will gradually cut through the wire strands, leading to poor contact and increased resistance.
  
  Technicians often encounter cable lengths that violate standards or long unshielded segments of red and green wires. Shielding quality should also be monitored—it degrades over time, especially in corrosive environments.

• Grounding and Bonding
  Proper grounding bonding in machines and control cabinets is crucial for network stability. Inadequate grounding bonding can lead to parasitic equalizing currents that disrupt the signal even with shielding in place.

TIP: If there is an unshielded segment of cable, maintain the twist between the red and green wires. You can protect the cable using a shielding sleeve.

What the Analyzer Reveals – 1 + 3 Oscilloscope Waveforms

Analyzer curves quickly reveal that something is wrong. However, diagnosing the cause requires know-how and experience. Let’s examine 3 common PROFIBUS sins and how they manifest in waveform distortion.

 

Good Signal Example

A clean, regular waveform with no noise, reflections, or distortion. The square shape matches binary data transfer (1s and 0s), and the voltage levels are correct.

  Long Rise Times

Sin: The PROFIBUS segment is too long.

Solution: Split the segment using a B1 repeater to create two isolated segments. Interference from the first half will not affect the second.

  Noisy Waveform

Sin: Cable runs too close to power cables or there is poor bonding.

Solution: Ensure cable spacing follows standards or use shielded barriers. Check bonding.

  Heavy Signal Distortion

Sin: Termination resistor is off at the segment’s end (the last station). The signal is not absorbed but reflects back, causing distortion.

Solution: Activate the termination resistor at the segment's end and remeasure the signal.

The Termination Trap

You may know the scenario: A station stops responding or disappears from the network. Maintenance naturally checks the station or its surroundings. But with PROFIBUS, the cause might be a disabled termination resistor at the opposite end (the last station) of the network. At FOXON, we call this the “Hiroshima Effect”—and we will be happy to explain it at our training sessions.

Extend PROFIBUS Life with Proper Care

There are, of course, many more potential PROFIBUS issues. The topic is broad enough for a two-day training course on diagnostics, repairs, and upgrades at the FOXON Academy. You will learn about other pitfalls like T-taps, leakage currents, or cable induction. You will also find out which cable lengths match your communication speed—and discover how to apply the Rule of Three Sisters.

Start caring for your PROFIBUS today by downloading and reading the The 10 Commandments of PROFIBUS on our blog at foxon.cz.

Download 10 Commandments of PROFIBUS

👁️ Install permanent monitoring on key production lines and devices using PROFIBUS—you can even monitor the network from your phone

🔍 Get a diagnostic analyzer for periodic checks and catch issues before they lead to downtime

⏳ Don’t have time to monitor your network? Leave it to us. We offer both permanent monitoring and one-off diagnostics. Our strength lies in prevention. Don’t wait until your PROFIBUS counts all your sins and fails completely. Contact us: enquiry@foxon.cz.

TIP: Get a handy cable stripping tool to simplify connector and repeater installation ▶️