There is no doubt that industrial pc play a big part in industrial control, but what form they take and where they are located also play an important part. A mainframe business computer performing the paperwork and assisting management in a factory or plant is one thing, but the micro or mini industrial computer on a factory or plant floor or in a control room, no matter what task it assigned to it, is another thing.
PCs in the Factory
Major changes have been taking place in the industrial and process control field. Influenced by the flurry of activity and innovation in the personal and office computer markets, control system users have been evaluating and using smaller, less expensive alternatives to large-scale, computer-based process control.
A key factor behind the move of the computer into control rooms and onto the factory floor was its flexibility; engineers could easily reconfigure their systems as control needs changed. The computer's capabilities could often be expanded, in many cases without having to purchase additional equipment or increase the area of the control room. Although the computer could not perfectly emulate an analog controller or strip chart recorder, it opened new possibilities for the optimization of control and generation of more detailed and accurate management information.
The hardening of computer systems against harsh industrial environments further encouraged their use in control applications. They were repackaged with larger power supplies, became more tolerant to heat and humidity, and used air filtration systems, to name some industrial adaptations. The advent of multitasking and real-time operating systems enabled computers to handle many tasks simultaneously, making them more cost effective and flexible than dedicated, single-use systems.
Early systems had three serious disadvantages:
• Most were programmed in assembly language or a proprietary language, thus requiring ongoing vendor or inhouse software maintenance.
• The computer was relatively expensive. A significant number of loops had to be placed on the computer (or a number of jobs eliminated) to justify system expenses.
• The systems had limited man-machine interface capabilities-black-and-white text or semigraphic CRTs were standard, color was a luxury. In some cases, electomechanical panels were included in the system to give the operator a familiar method for performing their work.
Major system vendors spent a great deal of time and money engineering their systems to overcome this weakness. As a result, today's computer tools feature:
• Menu-driven configuration that requires no programming on the part of the end user;
• High system security (including data integrity, operator safeguards, memory-resident software and in some cases, redundancy); and • Man-machine interfaces that cater to the operator by providing unambiguous displays and commands.
Note that many of the above were available before the introduction of the IBM PC. While there are still many good systems based on fine equipment from such companies as DEC, Hewlett-Packard, and others, the PC has flooded the general market and, in the process, changed many points of view. A careful examination suggests that:
• The control industry is going through the same qualification and justification steps that it went through 30 years ago, when process computers were introduced;
• A changing economy has made justification of multi-million dollar systems more difficult, forcing users to look for cost-effective alternatives;
• Users expect large-system support at PC prices;
• New, qualified vendors have entered the market with small systems, while some of the traditional vendors have not produced small microcomputer systems;
• The burden is on the user to determine whether his claims for system features exist and whether a given system will solve the problem.
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