Measuring for Keeps

摘要

The fundamental principle of measurements, one I've discussed many times in this column, is that measurement uncertainty can be determined in most situations. If the process of measurement does not affect the item being measured, repeated measurements of a single item will yield statistical information about the variability of the measurement process. But what if measurement does change the item being measured? Is there anything you can do to characterize your measurement uncertainty? Many tests and measurements do not leave the measured item, the unit under test (UUT), unchanged. The UUT is often a single-use item, such as an automotive air bag infla-tor. These inflators are tiny explosive devices that rapidly emit a large puff of vapor (enough to inflate an air bag in a few milliseconds). These devices cannot be 100% tested.