Far-reaching consequences of software and hardware decisions
These examples clearly illustrate the strategic implications of a decision to opt for one type of software or another. Once a decision is taken and a particular system introduced, a company will have to live with the programs and remain at the mercy of the provider’s release planning for years to come. The effort and expense involved in maintaining and operating installed hardware and software and the different communication components rise with each passing year of use. While process control systems installed on workstations were once expected to run for up to 20 years, this does not apply to PC-based standard components. Once the running repair and maintenance costs begin to rise disproportionately or competitiveness is compromised by the lack of any further scope for upgrading, systems are pronounced ripe for modernization. As in the case of the car manufacturer mentioned above, the plant software is a depository for a company’s entire pool of expertise, encompassing all the technological regulations, proven control algorithms and plant operator displays. The sheer complexity of this type of porting or migration is accurately illustrated by the quantity structure of a control system used in the Ruhleben sewage plant run by the Berlin Water Board, one of Germany’s biggest water utility and waste water treatment companies.
It operates a 9,400 kilometer long sewage channel network with some 225,000 connecting pipes and 147 pumping stations, purifying over 220 million cubic meters of water every year. At the time of its modernization, the process control system in Ruhleben comprised ten operating stations encompassing more than twenty monitors in four control rooms. The sewage treatment plant was monitored and regulated by 45 automation systems.
The control system managed over 750 process displays and 650 graphs charting 1,800 drives and 2,700 measurement points. In total, the system was capable of issuing around 20,000 individual messages and processing more than 210,000 variables. The changeover was staggered over two implementation stages: First of all the software was adjusted to the new system on a tool supported basis. This step-by-step modernization process permitted the retention of system peripherals, sensors and input/output modules. Following their recommissioning, these systems continued to work with the same technological accuracy as before. Step two was to modernize the hardware, which entailed rewiring, exchanging modules, setting the distribution boxes and performing a system test. The changeover was performed alongside running operation without causing major disruption.
As this modernization process illustrates, plant owners should always opt for an IT infrastructure which allows flexible and simple integration into existing architectures – even if only for cost reasons. However, apart from a precious few exceptions, no uniform standard exists for connecting different production areas and levels. Machine and plant manufacturers tend to equip their products with the most suitable operating system for the job in hand. Each is fitted with its own communication interface for data exchange, which is not necessarily chosen with the focus on integration capability. This is perfectly in order where machine tools, printers, conveying devices or tanks and overhead reservoirs are remotely located or operate in isolation. However, where these components are installed as part of a networked production facility, what emerges is a highly complex and heterogeneous process landscape linked by a myriad of interfaces which compromise the clarity of the information flow. When the time comes to modernize the system, if not before, this gives rise to substantial additional expense as well as entailing considerable development and porting costs.