Computers come in many shapes and sizes


C omputers on the factory floor? Revolutionary thought? Actually, it's not really new. Various types of computers have been used in manufacturing for many years. VMEbus computers have been widely used in test stands and data acquisition. OEMs have used embedded computers as machine control for some time. Some will even argue a PLC is a type of computer. However the growing popularity of PC-based control has sent many controls engineers to the Control Engineering Control & Automation Buyers Guide as well as the Internet searching for the appropriate piece of hardware for control.

Ever look inside the PC on your desk? If you haven't and have a weak stomach, then don't. It will be covered with dust, cobwebs, lint, and other assorted things. Take that thing out in the shop to control a machine or process? No way! But many engineers are doing just that. Many manufacturers put a PC in an industrially hardened case to keep out dust and even liquids.

Inside a PC is usually a motherboard that contains the CPU, memory chips, and assorted electronics. The motherboard has bus connectors, also called slots, for the ubiquitous ISA cards. With the need to support ever faster CPUs and memory, PCI, a bus with higher bandwidth, was developed. PCI cards were originally video and sound, but now many manufacturers supply cards for industrial automation including vision, motion, and other I/O devices.

Some manufacturers also supply passive backplane ISA computers. Just as the name has it, the board containing bus connectors has no active intelligence. Users must add a single-board computer in addition to all the necessary peripheral cards.

Several specialty computer form factors have been developed to meet various industrial needs over the past several years. Among these are PC/104, STD 32, and CompactPCI.

PC/104 derives its name from its connectors-one connector has 64 pins and the other 40 for a total of 104. These modules are relatively inexpensive and are ideally suited for many embedded control applications. The modules are stackable providing many functions in a small space. Available modules include single board computer, digital and analog input/output modules, communications cards, video, and analog-digital converters.

STD 32 Bus combines small industrial-strength architecture with the performance of personal computers. Like larger, more expensive buses such as VME and Multibus II, it supports 16- and 32-bit data transfers across the backplane, without the multiplexing of signals. Other performance characteristics include multiprocessing, 32-bit addressing, high-speed Direct-Memory Access (DMA), slot specific interrupts, and hot swap capability.

STD 32 cards are secured on all four sides by the enclosure, with top and bottom card guides, the backplane connector, and a locking retaining bar. Some STD 32 computers are available with an extended operating temperature from -40 to 85 degrees C, while others feature enclosures designed for extreme conditions. The combination of board size and PCB thickness help prevent undesirable flexing in high vibration environments, allowing STD 32 systems to fly in space shuttle missions. These systems run software like a PC, enabling system designers to use PC development tools and such operating systems Windows 98, Windows NT, Windows CE, QNX, VxWorks, and other PC-compatible operating systems.

CompactPCI bus is a high-performance bus architecture based on standard PCI electrical specification. Implemented in rugged Eurocard packaging, it is typically mounted in rack mount enclosures housing 6U and 3U computer cards. Compared to desktop PCI, CompactPCI supports twice as many slots (8 versus 4) and offers a packaging scheme that is better suited for industrial applications. Cards are mounted vertically allowing natural forced air convection cooling. The pin-and-socket connector of the CompactPCI card is more reliable than the card edge connector of standard PCI cards. Power and signal pins are staged to allow support for hot swapping.

No matter what challenges that new application presents, there is a computer form factor to help overcome them. Be aware of all the alternatives, then choose wisely.

Gary A. Mintchell, senior editor

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