PCs Adapt to the Factory Floor
PCs have traveled the long road from hobbyist's basement to word processor's desk, to engineer's workbench, to plant control room, and now can be found in all types of environments, executing industrial software. The trip has not been as easy one, nor one without its detractors. Despite comments that the "personal" is being taken out of the PC and with heed to warnings on the use of a disk-based operating system in a closed control loop, engineers continue to apply PCs to a growing list of control applications.
One reason for this is the vast amount of MS-DOS software available for industrial control. A quick look through computer and trade publications reveals a number of interesting software products for PC-based design, monitoring, and control. Another reason for PC proliferation is the significant improvements made in the electronics and packaging of PCs. When asked how industrial pc have changed since IBM introduced its first hardened PC, manufacturers cite a number of enhancements.
PC vs PLC
When the first industrial PCs were introduced, there was considerable skepticism. Frequent comparisons between the PC and PLC usually rated the PC on the short side. Since then, the electronics and packaging engineers have taken a good look at PCs (PLCs) so that specifications for industrial PCs now meet or exceed those of the PLC.
Many manufacturers have designed their PCs to be more PLC-like. Packages have become modular, with models available in NEMA-rated enclosures; communication ports are optically isolated; and operating specifications have been expanded to include factory floor temperature and vibration levels. Many PCs for the control environment are based on a passive backplane system. Active and passive components are on plug-in, replaceable boards to increase system reliability and repairability.
A large growth area for ruggedized PCs is in their use as operator interfaces to PLCs. Nematron Corp. added a built-in monitor and keyboard to an AT. The result is its Ultra Workstation series which includes 14 and 19-in. monitors and bundled software products such as ScreenWare2 from Computer Technology Corp. and The Fix from Intellution. According to Nematron, a single industrial PC can replace an entire, complicated control panel consisting of hardwired components.
PC Bus Clones
Although IBM charted new territory with its Microchannel bus, the PC Bus remains the most popular architecture for factory floor PCs. The defacto standard created by an almost universal adoption of PC Bus and MS-DOS ensures many more years on the factory floor for the IBM PC clone. The following is a sampling of some of the products available. Well known for its Shoebox PCs, Action Instruments has 32-bit, 16-MHz, 80386-based BC-30 and BC-32 computers. As upgrades to Action's BC-20 and 22 computers, these units use the same passive backplanes and accept both XT and AT cards. Standard on-board RAM is 1 Mbyte, with expansion up to 8 Mbytes of RAM available on the processor board. With modular plug-ins and shroud packaging, the BC-32 is an example of a PLC look-alike.
Many industrial PCs are being applied as operator interfaces. The 80386 Industrial Workstation from Comark Corp. offers NEMA 4 or 12 packaging for its AT-compatible workstation and an integral tilt/swivel display. The 14 or 19-in. display is available with CGA, EGA, or VGA graphics and an optional touchscreen. The user has a complete operator-interface system including 80386 CPU, 2 Mbytes of memory, 19-in. display, membrane keyboard, a 720 Kbyte floppy disk drive, and a 40 Mbyte Winchester drive, all for under $10,000.
Although the IBM clone is king of the industrial PCs, there are exceptions to the PC Bus rule. One comes in the form of a Macintosh designed for industrial use. Back in 1987, Automatix Inc. introduced its AI90, an industrialized version of Apple's Macintosh II. Although NuBus is touted as an open architecture, Apple holds all rights to proprietary Mac logic. To build the AI90, Automatix buys a Mac II from Apple, strips it down to board level, adds some enhancement boards, and repackages it, all in a steel NEMA 2 enclosure. With its main business in the machine vision and robotics industry, Automatix offers a vision system based on the AI90, the Autovision 90. To the Motorola 68020-based AI90, Automatix adds its own vision software, ASAP.
A special network communication protocol provides 9,600 baud bidirectional communications among all the processors in the network. This permits real time transmission of data and programs between any two CPUs. It is even possible and desirable to have several independent tasks in a host PC communicating with different tasks in the same local processor over the single serial line.
In the large environmental control system mentioned earlier, there were five separate tasks communicating between each LC2 and its PC-AT host: one for LC2 access to the AT's disk; one for operator interaction from the PC-AT to the LC2; one to pass alarms from the LC2 to the PC-AT; one to pass data from the LC2 to the PC-AT; and one to pass data configuration commands from the PC-AT to the LC2. Although this may sound like a very complex communication design, the application code to perform all these functions in each CPU is much shorter and simpler than if all communications had been required to be channeled through a single message handler on each end of the line.
Data from multiple tasks can be displayed simultaneously on the PC-ATs text screen in real-time, using multiple windows. The factory network can handle any number of asynchronous tasks running concurrently, and can display any number of simultaneous windows of varying sizes, limited only by the screen size and the amount of data to be displayed. Pictorial data such as bar graphs from various tasks can be presented concurrently on the EGA high resolution graphics display. The use of multitasking communications can be illustrated in a representative screen display on the PCAT. The upper left, upper right, and lower left quadrants could be assigned as windows in three different LC2 slave processors.
Each processor could be asynchronously and concurrently updated as the data changes. At the same time, the lower right quadrant could show a concurrent interactive session where the operator at the PC-AT is changing some limits on the same LC2 processor that is providing data at the lower left of the display.
More info at Jawest .