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Hoffmann on Testing: Beware the Forgotten Spec!

September 23, 2010
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A “simple” request to add one more test to a test stand or assembly system is not all that simple most of the time.



From the point of view of a testing engineer, I cannot emphasize enough the necessity to thoroughly think through all the specifications for a test-intensive assembly system before formalizing an RFP.

A forgotten specification is no small matter, though some do not seem to grasp just why. The reason is complexity. Consider that the number of interactions in a system can be described by the following equation: n (n-1) / 2.

What does this mean? As an example, if you have seven tests in a system, you have the potential for 21 interactions. If you have eight tests in a system, you have the possibility of 28 interactions. What works best for one scenario is unlikely to work best in the other. Any specification interacts with others, especially from a software engineering perspective. Test circuit designs, the number of valves required, tooling costs, engineering hours, software design-it all adds up.

This means that a “simple” request to add one more test to a test stand or assembly system is not all that simple most of the time. It may impact other tests, require additional test circuits, fixture modifications, etc. Good engineering management will review all specs and keep only those that are essential. The alternative is a Rube Goldberg monstrosity and much larger engineering costs than would be necessary if forethought had been given at the start of the design process.

Of course, there are times when even the most basic decisions on test instrumentation may need to be revisited by an “afterthought” request for an additional test. Sometimes, if an additional test is required, a multichannel instrument can be substituted for the original single-channel unit. For instance, at InterTech we have multichannel leak-test instruments with up to four channels. When multiple tests are required, the cost-savings by using this type of leak detector are considerable.

Jacques Hoffmann is president of InterTech Development Co., which designs and builds equipment for leak testing, functional testing and automated assembly. He can be reached at 847-679-3377.

Editor’s note: “Hoffman on Testing” is part of a series of guest spots by industry experts that will appear regularly on ASSEMBLY’s blog page. Check back frequently to read more commentaries from Jacques, as well as contributions on automated assembly systems, machine vision, robotics and ergonomics.
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