Efficiently Cabled − Berlin Schultheiss Brewery Automated with PROFIBUS PA
This article provides a general presentation of the commercial and technical benefits that are leading to increasing use of PROFIBUS PA fieldbus technology in the food industry, plus an in-depth account of a specific project at the Schultheiss Brewery, Berlin, Germany (expansion of tank storage facility).

The history of the Schultheiss Brewery is closely linked to the traditions and historical development of Berlin. Back in the 1950s reconstruction was pursued continuously, based on state-of-the-art brewery technology. Nowadays the company operates according to an exemplary quality and environmental management system and with a beer output of approximately 1.5 million hectoliters it ranks among the large breweries in Germany. In line with corporate philosophy the company also opted for innovative and successful concepts when expanding its tank storage facility in 2002. Consequently, when integrating measurement engineering into the system level the company decided to use PROFIBUS PA fieldbus technology.

Project

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PROFIBUS is the vendor-independent industrial communication standard in automation technology, established throughout the world and defined in IEC 61158. In the meantime over 1,200 members are united in the PROFIBUS Nutzerorganisation e.V. (PNO) and the parent association PROFIBUS International (PI). Over 5,000 different PROFIBUS devices are available on the market; more than one million applications have been provided with PROFIBUS communication. Current market figures indicate an increasing trend toward using fieldbus technology, particularly in the food industry. The first PROFIBUS PA systems were installed in large breweries and were followed by more systems in dairies, the confectionery industry, and at refreshment drink manufacturers.

The crucial reasons for using fieldbus systems may vary enormously but the most important benefits can be described as follows: The highly simplified cabling compared to conventional 4...20 mA technology reduces the cost of installation and especially documentation. In addition to the fast PROFIBUS DP, PROFIBUS PA also offers the option of supplying a large number of field devices with voltage and power via a single cable. Despite relatively high cable costs there are saving potentials due to the topology. Other advantages can be found in the flexibility, which makes it possible to convert existing systems quickly or expand them easily. Over the last few years the rapid commissioning procedure in particular has become established as a very good benefit of the fieldbus.

Since the full measuring range of a device is transferred, there is no need to scale values in the programmable logic control (PLC) or in the coordinating control system. All PROFIBUS PA measuring instruments can be parameterized from a central point using commissioning software (operator tool). Considerable advantages are also provided by the field devices, which have many more functions and which can also be parameterized "offline", and thus put into operation directly. At the press of a button in online parameterization, suitable software programs automatically identify the bus slaves, which are then available for parameterization. If PROFIBUS devices of the same type are used in an application, e.g. in a tank storage facility, once configuration has been performed than it can be downloaded to the various field devices without any additional effort.

In order to reduce system down times the current status signals from the devices are sent to the central control panel by cyclic data transfer. In the event of a fault it is therefore possible to make a rapid diagnosis. It there is a malfunction, the output of the sensor can, for example, be assigned a fixed value temporarily (the so-called failsafe setting in the device). The PLC can even write relevant process information to the displays of measuring instruments, thus facilitating monitoring of the system in the field.

The permissible process limits are monitored in the device directly. This simplifies the amount of PLC programming. Furthermore, compared to conventional instrumentation there is more device data available from the fieldbus devices so it is possible to exploit the possibility of multi-sensor technology. For example, some measuring instruments record sensor temperature for internal compensation purposes. This value can be used as a comparative measurement for system monitoring or as a substitute value if the temperature sensor develops a fault.

For applications that place high demands on the accuracy of measurement it is advisable to use digital data transfer. Only then it is possible to avoid the inaccuracies occurring with conventional A/D converters and transfer the best possible measuring accuracy to the higher-level system. This advantage with the digital bus system is particularly useful in applications like precision automatic temperature controls, summators for flow meters, or high-precision density measurements.

With filling processes, which place high demands on data transfer rate, the fast PROFIBUS DP is employed. PROFIBUS DP is only used for data transfer and for this reason PROFIBUS DP devices are always 4-wire devices. The power supply and communication are thus provided by separate cables.

Now for the project example of Schultheiss: Within the scope of the project the system manufacturer Südmo, which specializes in the fields of chemicals, food and pharmaceuticals, was responsible for the process control engineering, visualization and automation. For reasons of system availability, cost reduction and quality assurance the fermentation/mellowing section was automated with PROFIBUS PA. In addition to a flexible and simple switchover of production processes to the various types of beer, precision automatic process control had to be implemented. Appropriate documentation and filing of production data had to be provided for analytical purposes. A short system retooling time had to be observed for commercial reasons and production reasons. Endress+Hauser, specialists in measurement engineering, not only supplied the measuring instruments but also provided consulting services for integration of the measurement data into the PLC, in order to meet the high demands in terms of measuring accuracy.

All in all, there are 37 tanks available in the fermentation/mellowing section for the various types of beer. The aim of the automation concept is to improve productivity by minimizing the fermentation control process interventions that have to be performed manually. At the same time, power consumption has to be minimized by means of systematic process control and optimal automatic cooler control. Another important demand placed on the system is a high level of reproducibility in order to achieve consistent product quality to high standards.

The precision automatic temperature and pressure control ensures a short fermentation time with optimal quality criteria. In the outdoor area the glycol cooler is equipped with fast-responding, high-precision pressure gauges (37 units) and temperature gauges (72 units) for that reason. Even though high-quality measuring instruments are used, the controller unit accuracy specified as having to be 0.14°C can only be achieved with digital data transfer. All the production processes are clearly documented with process reports and error histories. Graphic data processing allows a detailed analysis of the processes. From the data it is possible to detect deviations from the optimal fermentation process immediately and initiate optimization measures. For flexible adaptation of the system to production of various types of beer the formulas are stored in separate files. Here the fermentation process can be divided into a maximum of 15 individual steps and be defined accurately. New formulas or modifications can be integrated into the system quickly. When the formula has been called up and the batch number assigned, the fermentation process is started.

In the production control room the operator control and monitoring system in touch and the production database IndustrialSQL were installed by Wonderware. Authorization to the change system parameters is regulated with a password. Clearly organized, easy and reliable operation of the system creates a high level of acceptance for the automation technology among operating staff.

The structural situation of the tank storage facility is ideally suited for PROFIBUS technology. In cabling the 180 slaves (measuring instruments and control valves) it was possible to reduce costs considerably in comparison with 4...20-mA technology. Despite higher-priced cables savings were achieved in cabling, at the terminal boards, and in the control cabinets of the existing system.

Result

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Increasing use of PROFIBUS PA fieldbus technology in the food industry reflects the trend toward exploiting the advantages of digital communication with measuring instruments in new systems. The reasons are to be found in the short installation and commissioning phases. That means a rapid return on capital input − and optimal conditions for achieving a return on investment within only a few years. In the event of an error, status messages in cyclic data interchange facilitate analysis and help to preventively avoid system outages. This naturally has a positive impact on productivity. In special applications with high-precision automatic controls, density measurement or also filling processes, improved accuracy creates major advantages over traditional 4...20 mA technology. Taking the project example of the fermentation/mellowing process at the Berlin Schultheiss Brewery it is particularly the latter aspect that has been illustrated.