#11 - Diagnosing a PROFIBUS network

One of the best devices on the market for diagnosing a PROFIBUS network is ProfiTrace. 

In this post we will show you how to make a simple and effective analysis in a few moments.

• Hardware: Connect the Proficore Ultra module on one side to the USB of the laptop and on the other to a "piggy back" point of the PROFIBUS network, for example on the connector of the master (PLC) or of a repeater. The connector also has a terminating resistor, which is normally left OFF, ON only for special cases and conditions.

• Software: 
• Open ProfiTrace
• Click on Init ProfCore Ultra. A network scan will be made, in the Live List tab, identifying the address (node) of each device and the status of each node (the node number in red is the PROFIBUS Master and the PROFIBUS Slaves in blue), the BaudRate speed of the 1.5Mbps network. 

The Overview tab shows the general status of the network, the number of devices (Master and Slave), Baud rate, communication time (data exchange in ms).

In the Bar graph tab, the voltage difference between pins B and A is shown. Note the color code, green, yellow and the red line at 2.5V. As we mentioned in a  previous post , the ideal range for this voltage is 4V to 7V. It is important to check both modes: AB differential voltage and AB differential stable.

Note: it is recommended to look at the bargraph physically connecting at different points in the network, as for example on the Master PLC, but also on the Repeaters.

• In the ScopeWare tab we have a high frequency oscilloscope, to visualize the signal shape (wave) of each node. This function is extremely important for diagnosing the signal and finding any reflections or flaws. The waveform is quadratic. It is important to check that the system voltage is 1V when the system is not communicating, which indicates a good network condition.

• ProfiTrace also has an option to create reports in automatic mode. Just click on Report> Generate Report. This report includes key information from the analyzed network, as well as several oscilloscope images from each node, which help in investigating problems. 

A common mistake is in identifying the location that is causing the network problem. For example, if a terminating resistor from the Master is OFF and should be ON, the master will be normal when looking at the oscilloscope, and the reflection problems will be amplified in the following devices, not in the Master. Therefore, it is important to be aware of this point.