Editor’s note: This is the second of a two-part series on leak rate testing. Read part one here.
Today’s topic concerns another “imagined” leak rate standard: accuracies that are one or two orders of magnitude more precise than any equivalent application in the same industry.
When we track down the origin of such requests, we often find they are the suggestion of a quality manager, who in due-diligence research of leak tester options finds a printed accuracy of a particular sensor and decides he should settle for nothing but the best. Why shouldn’t he, you rightfully ask?
Here’s the problem—or set of problems, more accurately. The sensitivity of a leak test sensor—or for that matter any nondestructive testing sensor—is not the same as the precision of the leak test instrument or the leak test system. Leak test sensors operate in a system, and the sensor alone does not determine overall system accuracy or gauge repeatability and reproducibility (R&R) of the leak testing system. In any leak test solution, the sensor is combined with electronics, cabling, valves, regulators, tubing, pressure gauges, and other components that affect accuracy. Further, when that leak test system is operating in a semi- or fully automated system, the effects of fixture and seal design, temperature, and cleanliness will also affect the accuracy and cycle time for testing.
Simply put, sensor accuracy and leak test system accuracy are not identical.
The request for a stricter leak rate standard that has little relation to how a product or component actually functions in the real world is not simply a problem of someone overpaying for something they don’t need. If only it were that simple.
The waters get even murkier because within the industry there is confusion about this inherent divergence between sensors and systems. It is even more insidious in that some published tester accuracies might be considered far-fetched to those more familiar with the factors that affect leak testing.
Here’s a tip for determining how “real” a stipulated leak tester accuracy is: Ask the testing facility to perform a standard gauge R&R within your defined test parameters and cycle time. If its representative suddenly starts backing away or his eyes glaze over, you should start looking somewhere else for a solution.
Most appropriately, due diligence to define acceptable leak rates and R&R should begin with consultations with leak-testing specialists about how your product or component functions. Typically, within a day you’ll get a detailed blueprint of what type of leak tester is the best-match technology for your real-world requirements. You will know what your accuracies will be, your cycle times, and so forth.
Physics, not fiction, should point you to best-match leak detectors. If leak testing is not currently front of mind, you can apply this advice to every calibrated system used by your operation to ensure quality.