Printing Press builder solves Profibus communication problem

May 30, 2010
Softing Inc.
Case Study

Summary

The signal quality on the PROFIBUS network was insufficient to sustain a robust communication link. Lowering the baud rate to 1.5 MBit/s immediately fixed the signal quality level on the affected machines.

May 30, 2010 - An unnamed manufacturer of printers is employing PROFIBUS technology in most of its high-tech printing machines. Typically, PROFIBUS is a very robust communications protocol. However, at times the engineering team was plagued with unidentified intermittent communication issues based on poor electrical signal quality levels. In the past, it was difficult and time-consuming for the engineering team to pin-point the exact location causing the problem. Consequently, the team was looking for a diagnostic tool that was able to

quickly pin-point the location of the problem with minimal effort

evaluate the overall signal quality of the PROFIBUS network and, most importantly,

provide information about the signal quality that an engineer could depend on

The printing machine manufacturer identified Softing's PROFIBUS Electrical Tester as the best-in-class tool that more than satisfied their requirements. Using this tool the engineering team immediately noticed that the overall signal quality on the PROFIBUS network was insufficient to sustain a robust communication link. However, what caused this poor signal level? Applications involving motion-control certainly have very strict timing requirements. Design engineers usually presume that the communication system is the bottleneck of their motion-control process. More often than not, the highest possible transmission speed (12 Mbit/s with PROFIBUS) is selected – just to be on the safe side. On the flip-side, a PROFIBUS network running at 12 MBit/s displays a dramatically increased vulnerability to electrical disturbances that can lead to erratic communication failures. In fact, running a PROFIBUS network at 12 MBit/s in a production environment is far from recommended. In other words "it is possible to have too much of a good thing." A better approach is to run a PROFIBUS network "as fast as necessary and as slow as possible" to maximize the robustness of the communication system.The main reason for the poor signal quality levels was that the design engineers initially configured their PROFIBUS network to run at 12 Mbit/s. The engineering team analyzed the bus-cycle-time at 12 Mbit/s and at 1.5 Mbit/s. The bus-cycle-time is the time it takes a PROFIBUS master to complete one data exchange cycle with all connected devices. The calculated bus-cycle-time was compared to the PLC's computing time (the time it takes a PLC to run once through its program) and it became obvious that it was more than sufficient to run the network at the significantly lower baud rate of 1.5 Mbit/s.Lowering the baud rate to 1.5 MBit/s immediately fixed the signal quality level on the affected machines.About SoftingIn industrial automation, Softing is a specialist for fieldbus technology and has established itself as a world-leading partner for networking automation systems and control solutions. Softing provides customers the key technology to connect devices, controls and systems with the leading communication technologies. In fieldbus technology, Softing is a world-class expert for Foundation fieldbus, PROFIBUS, and CAN/CANopen/DeviceNet. The company’s wide range of expertise includes solutions for OPC, FDT, and Real-Time-Ethernet protocols such as, PROFINET IO, EtherNet/IP, or Modbus/TCP. Many of the products and services developed by Softing since the company was founded in 1979 have become reference standards throughout the world. In addition, Softing has established itself as a provider of sophisticated diagnostic tools for fieldbus systems. Learn More

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