Inter-Laboratory Comparison Study Using Modular Instrumentation and Lessons Learned
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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.

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Inter-Laboratory Comparison Study Using Modular Instrumentation and Lessons Learned

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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


Resistance Measurement Verification in four-wire mode Second ILC (2012)


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


Questions?


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