Helium Mass Spectrometer Leak Detection: A Method to Quantify Total Measurement Uncertainty

In applications where leak rates of components or systems are evaluated against a leak rate requirement, the uncertainty of the measured leak rate must be included in the reported result. However, in the helium mass spectrometer leak detection method, the sensitivity, or resolution, of the instrument is often the only component of the total measurement uncertainty noted when reporting results. To address this shortfall, a measurement uncertainty analysis method was developed that includes the leak detector unit’s resolution, repeatability, hysteresis, and drift, along with the uncertainty associated with the calibration standard. In a step-wise process, the method identifies the bias and precision components of the calibration standard, the measurement correction factor (K-factor), and the leak detector unit. Together these individual contributions to error are combined and the total measurement uncertainty is determined using the root-sum-square method. It was found that the precision component contributed more to the total uncertainty than the bias component, but the bias component was not insignificant. For helium mass spectrometer leak rate tests where unit sensitivity alone is not enough, a thorough evaluation of the measurement uncertainty such as the one presented herein should be performed and reported along with the leak rate value.

References
  1. American Vacuum Society, “Calibration of Leak Detectors of the Mass Spectrometer Type”, J. Vacuum Science and Technology, Vol. 10(4), Jul/Aug 1973.
  2. American Society for Testing and Materials, “Standard Terminology for Nondestructive Examinations”, ASTM E1316-14, West Conshohocken, PA, 2014.
  3. Jackson, Charles N., Jr., and Charles N. Sherlock, Nondestructive Testing Handbook, third edition: Volume 1 Leak Testing, Columbus, OH, American Society for Nondestructive Testing, 1998.
  4. American Society for Testing and Materials, “Standard Practice for Leaks Using the Mass Spectrometer Leak Detector in the Inside-Out Testing Mode”, ASTM E493/E493M-11, West Conshohocken, PA, 2011.
  5. American Society for Testing and Materials, “Standard Practice for Leaks Using the Mass Spectrometer Leak Detector or Residual Gas Analyzer in the Tracer Probe Mode”, ASTM E498/E498M-11, West Conshohocken, PA, 2011.
  6. American Society for Testing and Materials, “Standard Practice for Leaks Using the Mass Spectrometer Leak Detector in the Detector Probe Mode”, ASTM E499/E499M-11, West Conshohocken, PA, 2011.
  7. Varian Vacuum Products, Introduction to Helium Mass Spectrometer Leak Detection, second edition, 1995.
  8. Pryor, Jeff M., and William C. Walker, “Pressure Change Measurement Leak Testing Errors”, Materials Evaluation, Vol. 72, May 2014.
  9. American National Standard for Calibration, U.S. Guide to the Expression of Uncertainty in Measurement, ANSI/NCSL Z540-2-997 (R2007).
  10. Bevington, Philip R., and D. Keith Robinson, Data Reduction and Error Analysis for the Physical Sciences, third edition, McGraw-Hill, New York, 2003.
Metrics
Usage Shares
Total Views
89 Page Views
Total Shares
0 Tweets
89
0 PDF Downloads
0
0 Facebook Shares
Total Usage
89