Improving PROFIBUS signal levels with a repeater

Introduction 

In late 2024, JCOM Automation became a distributor for Indu-Sol products. Before taking on any product line, I like to understand the equipment personally. Our philosophy is simple: we only sell tools that we believe in and would use in the field ourselves. I purchased a few of their products and tested them. They were innovative, well designed and well made. 

Last summer I was speaking with Octavio Schmiel, Head of International Sales for Indu-Sol. During our conversation he mentioned that Indu-Sol had what he believed to be the best PROFIBUS repeater on the market.  

I trust Octavio, but engineers tend to be skeptical of claims like that. The only real way to evaluate a tool is to use it in a real network. 

So, I purchased one and put it in my field service bag. It did not take long before I had an opportunity to test it. 

 Indu-Sol Multirep family portrait           Indu-Sol MULTIrep PROFIBUS repeater family 

 

The situation 

I was called to a site that was experiencing significant network noise. The plant had recently upgraded several drives, and the newer models were generating considerably more electromagnetic interference than the older equipment. 

The PROFIBUS network was struggling. 

The PLC sat roughly in the middle of the network, with drives on one side and power meters on the other. The interference was strong enough that I could stabilize communication on one side of the network, but not both sides at the same time. 

This type of situation can often be solved by using a repeater. Fortunately, I had the Indu-Sol MULTIrep X2 two-port repeater in my service bag. I installed the repeater at the PLC and separated the network into two segments. 

I was shocked! I expected the signal to be improved, but it was perfect!

I have worked with many repeaters over the years, and my general assumption had always been that most reputable repeaters perform roughly the same. I expected the network to improve. Normally, I would get about one volt to one and a half volts of improvement in signal strength. 

This was the first time I looked at the effect the repeater had on a network and thought: “Wow — that made a significant difference.” Below are two screenshots. The first shows the signal level without the repeater. The second shows the signal levels afterwards.  

     PROFIBUS signal levels before using the Indu-Sol repeater

 

     PROFIBUS signal levels after using the Indu-Sol repeater

Comparing Repeater Signal Levels 

A few weeks later I was investigating a separate issue involving a Siemens PROFIBUS repeater operating at 12 Mb/s. During that work I had the opportunity to compare the signal levels produced by several different repeaters. 

The measurements below show the signal level of a device on segment 2, as measured from segment 1, while a partial short between A and B existed on segment 2. The signal level of the device on segment 2 was 1.5 Volts.  

All the repeaters improved the signal level. However, the Indu-Sol significantly improved it by over one volt higher than anyone else.

 

Why PROFIBUS Signal Levels Matter 

In a PROFIBUS network, receivers require a minimum signal level of approximately 2.5 volts to reliably interpret data. Communication may still function below this level, but the probability of bit errors increases significantly. 

  • 4 V or higher → strong signal 
  • ~3 V range → acceptable but less robust
  • below 2.5 V → errors become likely 

Low signal levels most often appear on long segments or networks affected by electrical noise. This is one reason many technicians, including myself, shorten the maximum distances recommended in the PROFIBUS guidelines — not because the standard is wrong, but because real-world signal levels often start lower than expected. 

     Guidelines vs. real world distances

  

In the case of the MULTIrep by Indu-Sol, since it starts off so high, the segment length will be able to be longer than if you had used another repeater. This repeater will be able to give the end users the full distances as promised by the PROFIBUS guidelines.

Conclusion 

Based on the real-world tests I have conducted, my first pick for a PROFIBUS repeater is now the Indu-Sol MULTIrep. It is a pretty impressive PROFIBUS repeater.  

 

Need a deeper understanding of PROFIBUS troubleshooting? 

We also offer PROFIBUS training that covers signal levels, noise, installation problems, and practical network diagnostics. See our PROFIBUS training courses. 

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