An interlaboratory comparison (ILC) of helium low flow measurement capability was recently completed. The comparison was piloted by The National Institute of Standards and Technology (NIST); the majority of the data was taken over a period of approximately 2 years. A final round of data was taken by the pilot lab approximately 3 years after the data from the other participants was collected. The participants included a mix of 10 industrial and metrological calibration laboratories within the United States. The comparison was performed using three helium permeation leak artifacts having different flow rates within the range of 10-13 mol/s to 10-11 mol/s (10-9 to 10-7 std cm3/s). Each participant laboratory was required to measure the helium flow rate of all three artifacts at a nominal artifact temperature of 23 oC, and to submit a report of their results to the pilot laboratory, including a complete uncertainty analysis. The pilot laboratory made measurements at the beginning, end, and at three other times during the course of the comparison. The reference values used to compare the flow measurements from each lab were defined as the weighted linear fit to the pilot laboratory measurements. Analysis of the comparison results is presented along with an assessment of each participant s equivalence to the reference value for each flow artifact. The goal of this work is to help the participant laboratories to quantify their capability in the area of low helium flow measurements. Information of this sort is often required for quality system documentation and certification by organizations such as The American Association for Laboratory Accreditation (A2LA) and The National Voluntary Laboratory Accreditation Program (NVLAP).
Citation: NCSL International Measure
Pub Type: Journals
A2LA, calibration, helium leak artifact, helium leak detection, intercomparison, low gas flow measurements, low helium flow, NVLAP, primary calibrations