At almost 150 years old, DS Smith's Aschaffenburg paper mill is one of the oldest in Europe. It mainly produces corrugated base paper with a low grammage - and has been doing so from 100% waste paper since 1990. The machine used here produces up to 1400 meters of paper per minute with a width of 7.53 meters. As a result, the Aschaffenburg paper mill can deliver 400,000 tons of paper per year.

This performance is made possible by a high and consistent level of automation in the regularly modernized mill, which, in addition to the paper machine itself, includes the waste paper processing areas, biological treatment plant, water treatment plant, waste incineration plant and the gas and steam turbine power plant. These areas are combined under a central process control system. One key to this is the continuous exchange of data, which is handled via Profibus.

Even if this fieldbus stands for robust digital data transmission, it must still be taken into account with regard to day-to-day operation that, regardless of a flawless installation, the operating reserves for fieldbus communication can progressively decrease over time, ultimately leading to serious communication faults. This can be caused, for example, by EMC influences, defective connectors or a faulty bus termination, such as those caused by severe oxidation. Sudden production downtimes and the associated financial losses are the result.

The Aschaffenburg paper mill was also affected by this problem. However, DS Smith did not want to accept such failures and decided back in 2009 to improve the situation in the long term by continuously monitoring the status of the Profibus networks. The first step was to define the requirements for this. The solution had to be able to be used without impacting on the paper mill's existing systems and not cause any additional work for employees.

With this in mind, DS Smith intensively tested various devices for continuous Profibus monitoring over several weeks and ultimately opted for the 'TH Link Profibus' solution from Softing. This is installed stationary in a control cabinet and offers controller-independent access to the corresponding fieldbus networks without the need for special configuration tools. Even during operation, the components can be integrated into a system without any feedback. In particular, there is no need to change the bus addresses or adapt the control program.

The fieldbus monitoring module can be integrated into existing systems without feedback and requires little additional space for installation in the control cabinet.

© Softing Industrial Automation

One of the main advantages is the permanent network diagnostics via passive monitoring of Profibus telegrams. The cycle time is measured and critical events are detected - including the number of telegram and message repetitions, restarts of fieldbus devices, device errors and diagnostic messages. This data allows early conclusions to be drawn about the current status of the bus communication and impending errors while the network itself is still working perfectly. Individually definable limit values - such as the upper limit for permitted telegram repetitions - can also be used to quickly derive a summarized 'good/bad' statement about the operating status of the system from this data. All individual data can be retrieved via an integrated web server connected to a central process control system - eliminating the need for on-site checks. Based on this data, the solution described also offers intelligent troubleshooting assistance and statistics for optimizing the network configuration. Finally, a particular advantage is the automatic sending of an e-mail message as soon as the observed overall communication status changes from 'good' to 'bad'. Wolfgang Groß, who as an employee in the electrical, instrumentation and automation technology department at the Aschaffenburg paper mill is responsible for the use of the solution described, comments: "For me, the e-mail notification of an impending fault is an important function. This means that I always have a precise overview of the current communication behavior in all systems, even in the office environment, and don't have to determine the current status of the individual Profibus networks on site."

A key criterion for DS Smith's decision to use TH Link Profibus was that this device is not an active participant in the network that changes the communication behavior, but that it only passively listens to the telegrams sent. The first devices were installed immediately after the test in September 2009. As early as November, 15 more devices were ordered, so that all Profibus networks of the paper machine and the waste paper processing and biological wastewater treatment plant areas could soon be continuously monitored. The result: "Thanks to the continuous monitoring of our fieldbus network, we were able to reduce the downtime of the paper machine by half because we were alerted to weak points at an early stage and were able to rectify them in good time before the system came to a standstill," recalls Joachim Gutjahr, the head of the electrical, I&C and automation technology department at the Aschaffenburg paper mill. "This enabled DS Smith to reduce losses by a high five-figure sum in euros."

The possible error patterns

Based on the possibilities of the current Profibus standard, 'TH Link Profibus' recognizes error patterns of a decreasing operating reserve. These can be