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Fluke Digital Multimeter Calibration Manual

Fluke Digital Multimeter Calibration Manual

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Applying Measurement Uncertainty To
Digital Multimeter Calibration
An introductory study of measurement
uncertainty and its application to digital
multimeter calibration
Teleconference:
US & Canada Toll Free Dial-In Number: 1-(866) 230-5936
International Dial-In Number:+1-281-913-1100
Conference Code: 1010759559
©Fluke Calibration 2011
Basics Of Measurement Uncertainty for DMM Calibration
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Summary of Contents for Fluke Digital Multimeter

  • Page 1 Applying Measurement Uncertainty To Digital Multimeter Calibration An introductory study of measurement uncertainty and its application to digital multimeter calibration Teleconference: US & Canada Toll Free Dial-In Number: 1-(866) 230-5936 International Dial-In Number:+1-281-913-1100 Conference Code: 1010759559 ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 2 Welcome Greetings from – Fluke Corporation Everett, Washington, USA We are very pleased to bring you this presentation on measurement uncertainty for DMM Calibration. ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 3 Welcome Welcome and Thanks! This presentation is based on Fluke’s extensive experience with: − Use and design of calibration Instruments − Our experience and understanding of the problems faced when applying measurement uncertainty for both regular and accredited metrology Thanks for your time, we hope you find it both valuable and useful.
  • Page 4 Presented by Fluke’s Calibration Business Unit and Jack Somppi Electrical Calibration Instruments Product Line Manager jack.somppi@fluke.com ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 5 • Use Q&A or chat to send me questions or request clarification • There will be an opportunity throughout the discussion to pause and ask questions. • You can view the material using either full screen or multi window methods ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 6 Applying Measurement Uncertainty To Digital Multimeter Calibration An introductory study of measurement uncertainty and its application to digital multimeter calibration ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 7 • Study a simple but detailed example of calculating measurement uncertainty • Consider some benefits of automating measurement uncertainty calculations • Receive a variety of references for further research on this topic ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 8 • Understand measurement uncertainty with respect to DMM calibration • Appreciate to the benefits of automation • Have technical references for more detailed information • Obtain copies of this presentation via email ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 9 Measurement Uncertainty & Why It Is Important ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 10 • How is this taken into account in today’s calibration & metrology? − By applying & documenting the measurement uncertainty process to the tests being done ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 11 Individually analyzed, calculated, & documented measurement uncertainties are more thorough and are required to be considered - as stated in − ANSI/ISO/IEC 17025:2005 General Requirements for the Competence of Testing and Calibration Laboratories ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 12 − 5.4.6.1 A calibration laboratory, or a testing laboratory performing its own calibrations, shall have and shall apply a procedure to estimate the uncertainty of measurement for all calibrations and types of calibrations. ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 13 The reference standards and reference materials used • Methods and equipment used • Environmental conditions • Properties and condition of the item being tested or calibrated • Operator There are many contributors to uncertainty ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 14 The uncertainty of measurement & compliance statements to metrological standards c. Evidence of traceability When statements of compliance are made, the uncertainty of measurement shall be taken into account ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 15 They are calculated in accordance with the method described in NIST TN1297, for a confidence level of 95% using a coverage factor of approximately 2 (K=2).” ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...

  • Page 16: Measurement Uncertainty

    • For every measurement – even the most careful – there is always a margin of doubt • You need to know the uncertainty before you can decide whether the tolerance is met ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 17 “How is this Measurement Uncertainty obtained?” ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 18 But a standard technique was agreed upon & published in October 1993: ISO Guide 98 - Guide to the Expression of Uncertainty in Measurement (a.k.a. GUM) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 19 Guide to Expression of Uncertainty in Measurement http://www.ncsli.org and find it in the store under NCSLI publications NIST Technical Note 1297 http://www.physics.nist.gov/Pubs/guidelines/ contents.html Internationally, many metrology organizations publish similar GUMs ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 20 Questions? - about measurement uncertainty or why it is important ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 21 Measurement Uncertainty & Calibrating DMMs A study of applying the GUM to DMM calibration ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 22 First – lets look at the concept Our initial look – • Consider verifying a precision digital multimeter • With a hypothetical study of verifying the DMM’s measurement performance at 100 millivolts DC • Let’s briefly look at what measurement uncertainty could be in this case ©Fluke Calibration 2011...
  • Page 23 • Many other factors that could also contribute to uncertainty: − ambient temperature effects, thermal emfs, noise, loading, power line conditions, etc. • Consider all factors and include if they significantly contribute to measurement uncertainty ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 24 (Often considered as systematic uncertainty) − Errors of the calibrating standards (performance specifications for accuracy changes over time and other conditions) − Inherent limitations of the unit being tested (DMM resolution limitations) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 25 − a basic estimate (representing one statistical standard deviation) − usually the RSS of all individual uncertainties (Combining uncertainties using such an RSS technique applies to uncertainties with standard relationships and are independent) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 26 • Expanding the calculated uncertainty through scaling estimates an uncertainty that covers this larger population -  • A coverage factor, , (often equal to 2), would indicate a 95% confidence. ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 27 = 100.0051mV 0.0004 mV • In this case,  0.0004 mV would be the resulting value of U calculated as shown below:   0004      ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 28 That describes the general process – are we okay so far? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 29 Next, a different and more detailed example… Examine the use of a Fluke 5500A to verify a 3.5 digit DMM at 10 Amps of Alternating Current at 50 Hz ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 30 − Variations of multiple repeated readings from the UUT − Effects of the system noise − Noise and short term variation of the standard • Now let’s examine the basic statistics … ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 31 • In our example, 5 readings are sufficient. Any improved uncertainties  for more readings are not significant versus required measurement tolerances (a typical DMM specification for this example test is ~ ±2.5%). ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 32  Then this uncertainty can be considered as non Standard Deviation significant of the Mean • One measurement value would be sufficient • The type B resolution uncertainty is adequate ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 33 Deviation from Average 10.07 +0.03 10.02 -0.02 10.01 -0.03 10.06 +0.02 10.04 0.00 10.04 (Average) s (Estimated Std. Dev.) 0.02549     25.5 mA     ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 34   Plus there are some other important characteristics to consider: − Probability Distribution = Normal − Sensitivity Coefficient = 1 What are these? − Degrees of Freedom = 4 ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 35 − Change in measurement response divided by the corresponding change in stimulus (usually a value of 1 in the case we are considering) For more information, see technical references on statistics ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 36  − Probability Distribution = Normal Grouped around a value − Sensitivity Coefficient = 1 Direct influence on response − Degrees of Freedom = 4 Based on 5 independent measurements ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 37 − lead effects, thermal emfs, loading, etc. • Estimates here are based on scientific judgment using all relevant information • Numerically, these are expressed as one standard deviation estimates for each different uncertainty ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 38 − Adjust as required for any appropriate factors such as legal traceability limitations, improvements for output characterizations, etc. − Convert to a ± one sigma confidence interval basis ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 39 • For this example, assume it is a certified calibrator that is routinely calibrated every year. • The absolute uncertainty specifications for 10 Amps, 50 Hz: 0.06% of output plus 2000 Amps ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 40 5500A – 1 year specs @10 A, 50 Hz ±(0.06% of 10 A + 2000 μA) is calculated to be: ±(6 mA + 2 mA) = ±8 mA ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 41 For example with a normal       3 2 distribution at 99% Normal Probability Distribution ±1σ = ±spec / (2.58) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 42 Fluke’s 5500A specifications The manufacturer’s specs document that specifications are based on a normally distributed, 99% confidence interval ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 43 ±1 sigma spec divide by 2.58 ± 8 mA / 2.58 mA = 3.1 mA 1 std. dev. This value should be smaller than the published spec! ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 44 ±1 sigma estimate of calibrator specification uncertainty  − Probability Distribution = Normal – as stated in the manufacturer’s information − Sensitivity Coefficient = 1  − Degrees of Freedom = ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 45 • Measurements include error due to resolution limits of the UUT - considered as one half of the • The of resolution for this UUT measuring 10 Amps is 10 mA (least significant digit) 10.00 10.00000 ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 46 Calculating The formula for   Calculates the standard uncertainty related to one LSD With an LSD of 10 mA - ± 2.9 mA at a 1 std. dev. ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 47 – Summary of is the ±1 sigma estimate of dmm LSD resolution uncertainty  − Probability Distribution = Rectangular − Sensitivity Coefficient = 1  − Degrees of Freedom = ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 48 2.9 mA • There are no other “B” uncertainties which are significant for this particular test (Note: It is often good to identify and document the other possible uncertainties deemed insignificant.) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 49 Combining all uncertainties …       Standard Combined Uncertainty    12.16 mA A One Standard Deviation Estimate Of Combined Uncertainty ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 50 11.410 Repeatability Normal  2.58 3.110 810 Calibrator Normal  2.910 510 Resolution Rectangular Current Assumed 12.1610 Combined Measurement Normal How do you calculate the overall effective Degrees of Freedom? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 51    • The formula considers each     uncertainty, each sensitivity    coefficient and each uncertainty’s specific value for degrees of freedom to calculate ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 52   (12.16            (11.4 (3.1 (2.9     Our effective degrees of freedom considering all our uncertainties ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 53 2.576 • For a large population with a normal distribution, 95% coverage 99.73% is calculated by k with a value of 1.96 (or sometimes 2 for convenience – giving 95.45%) ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 54 For our example with the effective degrees of freedom (V ) of 5.2, a coverage factor of 2.57 expands to a value with 95% confidence (compared to 1.96 for an infinite set of measurements/samples). ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 55 Expanded measurement uncertainty calculation   57  12.16  31.26 ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 56 (Amps) Freedom 11.410 Normal 11.410 Repeatability  2.58 710 Normal 2.710 Calibrator  510 Rectangular 2.910 Resolution Assumed Current Combined 12.110 Measurement Normal Assumed Current 2.57 Expanded 31.2610 Measurement Normal ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 57 • The final measurement value including the measurement uncertainty from the series of DMM measurements of the calibrator     Amps 0.031 At a level of confidence of 95% ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 58 = 100.9 1.005 1.66 1.984 2.025 2.626 3.077  1.645 1.96 2.576 − k = 1.984, 24 mA (1 mA better) improves only 7 mA by taking 73 more measurements ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 59 1.005 1.66 1.984 2.025 2.626 3.077  1.645 1.96 2.576 0.25A ÷ 31mA = 8.06) So to satisfy a minimum test ratio of 4:1, 5 measurements are more than adequate! ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 60 Questions? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 61 Making The Calculation Of Measurement Uncertainty Simpler What can you do to automate this? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 62 Automation alternatives • A custom program designed for a specific requirement • A custom spreadsheet for analysis • A commercial metrology based software package such as Fluke’s MET/CAL Plus ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 63 MET/CAL automates the uncertainty calculations Post test summary of 10.000A @50Hz Including: 5 reading average Calculated combined standard uncertainty How does this work? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 64 = 0.01216490061 data base. They accessible for reports Effective Deg. of Freedom = 5.186506 Total & future analysis. Standard Uncertainty = 0.01207040471 Uncertainty Coverage Factor = 2.567104753 Expanded Uncertainty = 0.031263794 ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 65 • There should be definite information to support answering any auditor’s questions • Keep records of the procedure’s measurement design with an uncertainty error budget • Be able to demonstrate the reasonableness of the test’s uncertainties ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 66 • Report writing flexibility permits properly configured certificates and data summaries • Lets the technical staff concentrate on the test quality rather than the rote mathematical & statistical processes ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 67 Automation questions? ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 68 • Measurement results are considered incomplete without a quoted uncertainty • Calculations usually require a statistical process on multiple measurements for each test • Automation can be a valuable support for measurement uncertainty calculations ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...

  • Page 69: Where To Go From Here

    ANSI/NCSL Z540.2-1997 (R2002) U.S. Guide to Expression of Uncertainty in Measurement http://www.ncsli.org and find it in the store under NCSLI publications NIST Technical Note 1297 http://www.physics.nist.gov/Pubs/guidelines/ contents.html ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 70 • Chapters 20-22 on Statistics & Uncertainty in the text book Calibration: Philosophy in Practice 2 . Edition • Fluke’s Training Course – Cal Lab Management for the 21st Century • Various reference material under technical papers at the resource library on Fluke’s web site: http://www.fluke.com...
  • Page 71 • UKAS Publication LAB-12 “The Expression of Uncertainty In Testing” http://www.ukas.com/ • NPL UK - “A Beginner's Guide to Uncertainty of Measurement” http://www.npl.co.uk/npl/ • Fluke’s “Calibration – Philosophy in Practice, Second Edition” ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 72 Still more references (3) • NCSL International: RP-12 - Determining & Reporting Measurement Uncertainties https://www.ncsli.org/ • NIST Website: Essentials of expressing measurement uncertainty http://physics.nist.gov/cuu/ ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 73 Questions      ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 74 Seminars” selection, and again click on the desired seminar selection, Our Seminar Topics Include: • Precision Measurement Techniques • Oscilloscope Calibration • General Metrology • Temperature Calibration • Metrology Software • RF Calibration ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 75 Cal-Book: Philosophy in Practice textbook More information: www.flukecal.com/training Members of the MET/SUPPORT Gold and Priority Gold CarePlan support programs receive a 20 % discount off any Fluke calibration training course ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...
  • Page 76 THANK YOU ! For material related to this session, visit our web site: http://www.fluke.com For any questions or copies of this presentation: email inquiries to: calibration.seminars@fluke.com ©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration...