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Inter-Laboratory Comparison Study Using Modular Instrumentation and Lessons Learned Author: Dimaries Nieves – National Instruments Senior Metrology Engineer Speaker: Jorge Martins – National Instruments Principal Metrology Engineer
Learning Objectives • How can we demonstrate performance and competence of modular instrumentation as part of metrology and accreditation process? • Propose a process to perform an Inter-laboratory Comparison using a modular instruments. • Standard Documents for ILC evaluation. • Review some of the results and lessons learned.
Inter-laboratory Comparison (ILC) is a key criterion for laboratory accreditation • ILC is an important asset in: • Measurement Reliability • Measurement Assurance • Calibration Process Confidence • Measurement Method • Technician Proficiency • There is no commercial proficiency testing available for Modular Instrumentation. For the last two years, National Instruments performed an interlaboratory comparison using Modular Instrumentation as the primary standard
Modular Instruments • Gradually taking an important role in test and measurement • Enable more cost effective and flexible measurements • Used in Research, Calibration, Validation and Production test • In metrology and laboratory accreditation process • Need to demonstrate performance and competence performing regular calibration services.
NI Inter-Laboratory Comparison Proposal • The ILC was designed based on: • NCSLI’s RP-15 • ASTM E691-13 • NIC Metrology Laboratory serves as the pivot Laboratory • Unit was monitored using the petal or flower model • NI Certified Calibration Centers were selected to participate
ILC Equipment Bias and Stability • Stability of the reference unit was determined by the pivot Laboratory before starting the ILC process. • No significant bias was found within the pivot measurements. • The pivot laboratory monitor the performance of the unit to ensure that any unexpected changes in the traveling standard are promptly detected. • Comparison of the pivot lab data showed that the unit remained in control throughout the all ILC.
ILC Reference Value • Reference values were determined using the pivot lab measurements. • All pivot runs were included in the analysis • Statistical Analysis of the data was performed • Uncertainties reported by the pivot laboratory include ILC process bias and deviations.
First ILC Run • NI PXI-4072 Flex DMM and LCR Meter (6 ½ digits DMM) • NI Published Calibration Procedure • “Verify Mode Only” procedure using NI’s calibration software, Calibration Executive • Participants use their own chassis, standards, and cables to perform the measurements • Report only one measurement result per point with an expanded uncertainty at 95% of confidence (k=2).
For Evaluation An En value was calculated for eachmeasurement provided for eachlaboratory
Resistance Measurement Verification in 2-wire mode First ILC (2011)
Resistance Measurement Verification in 4-wire mode First ILC (2011)
Second ILC Run • NI PXI-4072 FlexDMM and LCR Meter (6 ½ digits DMM) , Chassis and Cables (entire Setup). • NI Published Calibration Procedure • “Verify Mode Only” procedure using NI’s calibration software, Calibration Executive • Performed three runs on the unit, doing a manual “Self Calibration” before each run • Verify that the board temperature was stable at 35 ºC ± 2 ºC before performing the verification • Report measurement result with an expanded uncertainty at 95% of confidence (k=2).
Resistance Measurement Verification in 2-wire mode Second ILC (2012) Pivot
Additional Analysis • Consistency Evaluation • Within the laboratory • S = Standard Deviation for one laboratory • Sr = Repeatability standard deviation of the equipment • p = Number of laboratories participating in the ILC
Additional Analysis • Consistency Evaluation • Between Laboratory • Where, = Lab average minus the average of the lab averages • Where, Sx = Standard deviation of the lab averages
Within-laboratory consistency (k) for DC Voltage measurement Second ILC (2012)
Between-laboratory consistency (h) for DC Voltage measurement Second ILC (2012)
Conclusion • Modular Instruments meet the published measurement specifications, regardless of the combination of chassis, controller and measurement I/O. • However, for an ILC the higher requirements for repeatability and reproducibility make it advantageous to provide, not just the instrument but, the entire measurement system. • Including the entire system in the ILC reduces differences between participants, improving the correlation of data. • Several statistical tools are needed