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Tolerant of Tolerance?

Wouldn’t life be great if everything fit together perfectly? There would be no need for tolerance. However, for that to be the case, everything would need to be ideal and without variation. Therefore, unfortunately (or, maybe, fortunately), we all deal with measurements and materials and situations that are not ideal and are compromised in one way or another.

Often the challenge with tolerance comes down to misunderstanding, and the fact that we all now design with CAD tools which have levels of precision far in excess of the realisable parameters of the mechanical or electrical materials and measurement systems we deal with on a day-to-day basis. Poor understanding of tolerance or being intolerant of tolerance can lead to disappointment.

Or, as attributed to Aristotle, “It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible.” That translation itself is, of course, only an approximation and requires an appropriate degree of tolerance, but you get the idea.

Looking back a few decades, it is clear that the challenge in terms of tolerance and dimensioning shifted with the move from analog to digital measurements, and electrically there is the beginning of a second shift where high-speed digital systems blur back into the analog realm.

Those of us in the industry for long enough can recall the move from analog voltmeters to digital and from vernier scale to digitally encoded micrometers and calipers. Digressing slightly, I recall a very analog moment when, as a naïve 11-year-old, I and a school friend decided to measure the current available from mains electricity—with an analog AVO meter (safety note: not a wise move!).

The result was a large blue flash, melted meter cables and a visit from the local electricity authority as we had vaporised the main fuse in the supply box. Fortunately, we are both still here, and I still use a trusty old analog AVO meter for electrical jobs around the house. Perhaps that’s why I ended up with a career in the electronics industry, but I have to say it’s not as exciting as that first experience, and maybe that’s not a bad thing.

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Editor's note: This column originally appeared int eh March 2014 issue of The PCB Design Magazine.