In Product Testing, PCs Gaining On PLCs

The change agents: manufacturing's need for higher product tolerances, more detailed management reporting and results archiving. The enabler is the maturity of the PC.

Question: In product testing systems, will PCs overtake programmable logic controllers (PLCs)? Answer: Even though PLCs dominate, PC-based systems will win, predicts Drew Wilson, general manager of ATS Test Systems, Woodbridge, Ontario. (The organization is a division of automation supplier ATS Automation Tooling Systems Inc., Cambridge, Ontario.) "The change," he predicts, "will happen first in plants with automated test systems installed as part of total quality processes requiring full functional performance testing and detailed management reporting." Also driving the transition will be customers requiring more comprehensive testing. "Eventually the type of testing now common in the production of zero defect products such as heart pacemakers and automotive airbag systems will embrace most, if not all products." Wilson notes that PC-based systems are already commonplace in testing circuit boards. PC-based product testing brings more than the data acquisition advantages of greater bandwidth, he explains. "With PCs we can test to a much higher degree of accuracy, gain repeatability and perform a lot more testing in a shorter period of time." "Those performance factors are becoming more critical as production lines are designed for higher speeds and multiple product types," Wilson adds. "PC based systems give us the capability to test every unit of output as it is made and to compare what is happening with past product information." Wilson's argument is that tomorrow's production will increasingly depend on deeper, more comprehensive product testing information. He says the ongoing challenge is for systems to provide a stream of testing data rich enough to reflect actual product quality. His worst case example is motor coils. "A low bandwidth test of the total unit may suggest that all coils are working while a higher bandwidth signature analysis may show that some are not." Despite that reality, Wilson admits that PC-based systems still suffer a perception problem. He says the large installed base of PLC-based systems reflects on an unfortunate image that PCs undeservedly retain from the early days of the technology. The commercial development of PLCs dates to the late 1960s as companies such as General Motors Corp. encouraged an industrial strength replacement for relay logic control of production lines. PCs emerged later and were not initially intended for industrial application. Low level reliability and high cost are no longer PC characteristics, he contends. Based on the PC's ease with large volumes of test data, Wilson concludes with three predictions.

  • "Testing equipment makers will become more involved with the customer's initial product design stage.
  • "Maximizing testing success will depend more on managements devising the right instrumentation infrastructure for PC-based systems.
  • "And eventually the end of PLC-based systems-manufacturing's expectations will simply get too complex and difficult for testing to be handled by PLCs."
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