Accuracy Apples and Accuracy Peaches—What Does that Vendor Quote Really Mean?

It’s a noisy world, and that is one of many reasons why in leak testing and other non-destructive testing, “accuracy” is not “accuracy” in the way that a rose is always a rose.This is what I mean: if someone tells you that their leak tester can deliver 0.05% accuracy full scale for pressure decay leak testing, and let’s suppose it’s at 100 psi--- that would be an accuracy of 0.05 psi.

January 27, 2012

2 Min Read
Accuracy Apples and Accuracy Peaches—What Does that Vendor Quote Really Mean?

Sounds good, doesn’t it?  But you have to know that what you are being quoted is the accuracy of the transducer and not the accuracy of the entire leak test system. A transducer is simply taking an electrical signal and processing that signal from analog to digital and a clear value that we humans can look at. In any analog-to-digital conversion there are always noise factors that come into play. The speed at which you are testing, cycle times and the time you allow for stabilization also comes to bear on your ultimate measurement accuracy.

You can have the most sensitive and accurate transducer in the world but still come up with questionable accuracies in your measurements because of these inherent noise factors. Some leak test instruments with less thoughtful design have PC board layouts that tend to amplify noise—or rather, mitigate against your ability to control it. If tests are then also configured with inadequate fill and stabilization times that very fine sensor your leak test instrumentation uses won’t matter much.

There’s the accuracy of a sensor—let’s call that the accuracy apple. Then there’s the accuracy of the entire test system—let’s call that the accuracy peach. If you try to mix up the two the laws of physics will correct you every time.   

Joe Pustka

 

Putska (pictured on the left) is a medical device leak testing technical support manager for Uson, which first developed high accuracy leak testing methods for NASA, and since 1963 has specialized in leak detection, leak testing, and non-destructive testing for the medical device and medical packaging industries, among others. Putska works with medical device companies throughout North and Central America and has worked with Uson in various technical capacities since 1980.

 


 Image derived from Flickr user opensourceway

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