Basic concept of measurement

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CONCEPTS OF METROLOGY AND IMPORTANCE OF CALIBRATION Nihal Gunasekara Sri Lanka Bangladesh BEST Programme

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KEY WORDS CALIBRATION – Comparison METROLOGY – Science of Measurement TRACEABILITY – Unbroken Chain of Comparisons UNCERTAINTITY – Error in Measurement ACCREDITATION – Third Party Ascertain CALIBRATION INTERVAL – Equipment Remains Reliable Bangladesh BEST Programme

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3 3 WHAT IS METROLOGY SCIENCE OF MEASUREMENTS Everything has to do with measurement Designing Conducting Analyzing Results Experiment or test within the Metrology realm Allowing people to plan their lives and make commercial exchange with confidence CAN BE SEEN EVERYWHERE Bangladesh BEST Programme

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METROLOGY Metrology Covers Three Main Tasks: The definition of internationally accepted units of measurement The realization of units of measurement by scientific method Establishment of traceability chain in documenting the accuracy of a measurement “ Metrology is essential in scientific research” Bangladesh BEST Programme

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CATEGORIES OF METROLOGY Scientific Metrology – Development of measurement standards Industrial Metrology – To ensure the adequate functioning of measurement instruments used in industry, production & testing laboratories Legal Metrology or Weights & Measures – Accuracy of measurement where these have influence on the transparency of economic transactions, health & safety Bangladesh BEST Programme

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AREAS OF INDUSTRIAL METROLOGY Mechanical Metrology – Realises , maintains and disseminates the national measurement standards in the areas of Mass, Volume, Pressure and Dimension Electrical Metrology –– Realises , maintains and disseminates the national measurement standards in the areas of AC/DC, low frequency, time & frequency and temperature Bangladesh BEST Programme

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LEGAL METROLOGY Services offered by legal metrology are: Mass measurements verification : verification of all mass measuring instruments (balances, trade masses etc.) Volume measuring instruments : verification of fuel dispensers, tankers , meters etc. Prepackaging control :verification of quantities in prepackaged products (mass, volume, length, number etc.) Bangladesh BEST Programme

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8 Calibration ( Old Definition) “ Calibration is the comparing of an unknown measurement device against equal or better known standard under specified conditions” Bangladesh BEST Programme

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Calibration “ Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties, and in a second step, uses this information to establish a relation for obtaining a measurement result from an indication ” International Vocabulary of Metrology ) ( JCGM 200:2012 – International Vocabulary of Metrology ) Bangladesh BEST Programme

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10 Units of Measurement SI Units published by BIPM( Bureau of Weights and Measures ) Base Units… Quantity Unit Symbol Length metre m Mass kilogram kg Time second s Temperature kelvin K Electric current ampere A Luminous intensity candela cd Amount of substance mole mol Bangladesh BEST Programme

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11 Metrology Laboratories Primary Laboratories NML, NMI, NPL etc Reference Laboratories Calibration Laboratories Bangladesh BEST Programme

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12 Measurement Uncertainty “ non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used” It arises due to the imperfections in the measurement system No measurement system is perfect !!!!! Bangladesh BEST Programme

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13 Uncertainty An estimate of the possible error in a measurement Type A evaluation A series of repeated observations is obtained to determine the standard deviation of the measurement result . Type B evaluation The evaluation is carried out using available information found in calibration reports, certificates, specifications etc . Bangladesh BEST Programme

Expanded Uncertainty:

14 Expanded Uncertainty Calculate combined standard uncertainties Type A Type B Exp. Unc. U = Combined Uncertainty X Coverage factor Bangladesh BEST Programme

Ishikawa diagram :

15 Ishikawa diagram Uncertainty of an oven Calibration (B) Test oven Resolution (B) CJC (B) Scatter (A) Digital Thermometer Resolution (B) Reference T/C Bangladesh BEST Programme

Confidence Level:

16 Confidence Level Gaussian probability distribution -k σ  +k σ 68% Within 1 σ of mean 95% Within 2 σ of mean 99% Within 3 σ of mean Bangladesh BEST Programme

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17 Metrological Traceability ”property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations , each contributing to the measurement uncertainty ” or “ HOW TO ENSURE THAT TWO MEASUREMENTS OF THE SAME QUANTITIES ARE COMPATIBLE ” Bangladesh BEST Programme

How Do We Get Traceability ?:

18 18 How Do We Get Traceability ? Common point of reference My laboratory Your laboratory Their laboratory Bangladesh BEST Programme

NMI: The Link Organisation to the International Arena:

19 19 NMI: The Link Organisation to the International Arena International standards National community that is using measurements National Metrology Institute Bangladesh BEST Programme

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HIERACHY OF MEASUREMENT STANDARDS Instruments Used in Lab/ Industry Working Standards Secondary Standards Primary Standards Traceable to BIPM Bangladesh BEST Programme HIERARCHY OF MEASUREMENTS

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21 Metal fixed-point Number Substances State Defining temperature K o C 1 2 3 4 5 6 7 8 9 Hg H 2 0 Ga In Sn Zn Al Ag Au Cu T T M F F F F F F F 234.3156 273.16 302.9146 429.7485 505.078 692.677 933.473 1234.93 1337.33 1357.77 -38.8344 0.01 29.7646 156.5985 231.928 419.527 660.323 961.78 1064.18 1084.62 Bangladesh BEST Programme

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22 CALIBRATION HIERARCHY OF MASS STANDARDS BIPM Kilogram National Kilogram Class E1, E2,F1, F2 Masses Analytical &Top loading Precision Balances OIML M1,M2,M3 Masses OIML R47 Masses TRADE MASSES Platform & Top loading balances Weighing Bridges Bangladesh BEST Programme

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23 23 BIPM Prototype 1kg EXAMPLE MASS COMPARATOR Prototype 1kg Calibrate Traceable to Analytical Balance Transfer USE Set of Classes E2, F1, F2, and M1 Traceable to SI Units Bangladesh BEST Programme

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24 GAUGE BLOCK COMPARATOR Primary Standard Laser interferometer Traceable to Grade K set Grade 1 set USE Compare Calibrate Bangladesh BEST Programme

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25 Examples 1. Performance Test on a Incubator at 35 + 0.5 o C Set Temp . o C Indicator Value o C Measured Mean value o C Expanded Uncertainty o C Min Max Near Sensor Upper Middle Lower 34.5 34.5 34.6 34.9 34.7 34.5 34.2  0.2 Bangladesh BEST Programme

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26 2. Performance Test on a Water Bath at 50 o C S P C R Q Set Temp . o C Indicator Value o C Measurement Locations Measured Mean Value Expanded Uncertainty o C Min Max 48.0 49.5 50.0 C P Q R S 50.1 50.2 50.1 50.1 50.0  1 Uniformity : 0.61 o C Stability : 0.33 o C Bangladesh BEST Programme

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27 COMPARATOR BALANCES CLASS E 1 1 kg CLASS E 1 SET CLASS E 2 SET CLASS F 1 SET CLASS F 2 SET CLASS M 1 SET MASS Reference and Auxiliary Equipment Bangladesh BEST Programme

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28 CALBRATION INTERVALS What is Calibration interval ??? Period of time of use to ensure the equipment remains reliable Interval is too short : Calibration $$$$$ Interval too long : Risk of bad measurements Bangladesh BEST Programme

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29 CALBRATION INTERVALS ISO 17025 Requirements: Capable of achieving required accuracy Comply with specifications relevant to test/calibration method Use under established calibration programme Therefore need to : Define required accuracy Identify the equipment that can affect it Manage all equipment under a calibration programme Bangladesh BEST Programme

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30 RECOMMENDED CALBRATION INTERVALS N No single correct answer Calibration represents an instantaneous snapshot of actual condition Depend upon Level of stress - subjected Stability of past calibration Allowable tolerance range Required accuracy Quality Assurance Requirements Bangladesh BEST Programme

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31 RECOMMENDED CALBRATION INTERVALS Final Analys i s Period between two calibrations Determined & Monitored USER HIMSELF Bangladesh BEST Programme

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32 HOW TO ESTABLISH CALIBRATION INTERVAL Consider influencing factors and existing knowledge : eg Accuracy sought & consequences of error Manufacture’s recommendations Accommodation & environment Purpose and usage Maintenance & servicing Trends from previous calibration Frequency of checks Etc. etc. etc. …. Ref. - ILAC – G 24 : Guidelines for determination of calibration interval of measuring instruments Bangladesh BEST Programme

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33 33 RECOMMENDED PRACTICES Calibration at (planned) periodic intervals to ensure acceptable accuracy & reliability Shorten the intervals when results of previous calibration suggest it May lengthen intervals on basis of demonstrated performance Documented procedure for assigning and adjusting calibration intervals Fully documented re-calibration system Bangladesh BEST Programme

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34 CALIBRATION OF VOLUMETRIC GLASSWARE FLASKS CYLINDERS BURETTES PIPETTES ACCURACY CLASSES CLASS A – Higher grade CLASS B – Lower grade Bangladesh BEST Programme

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35 Example - Pipettes Nominal capacity(ml) Limit of Error (ml) Class A Class B 1 25 100 200 0.008 0.03 0.08 0.1 0.015 0.06 0.15 0.2 METHOD Gravimetric Method – IS0 4787 -2010 (Laboratory Glassware- Volumetric instruments- Method of Testing of capacity and for use) Bangladesh BEST Programme

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36 IN-HOUSE PERFORMANCE CHECKS (During Calibration Interval) ANALYTICAL BALANCES – Using a Calibrated Weight INCUBATORS - Using a Calibrated Thermocouple GLASS THERMOMETERS- Ice Point Bangladesh BEST Programme

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37 37 Importance of Calibration Assurance of accurate of measurements Ability to trace measurements to International standards International acceptance of test/calibration reports Correct diagnosis of illness (medical reports) Consumer protection (legal metrology) Meeting the requirements of ISO 9000 and 17025 Bangladesh BEST Programme

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38 Technical Competence of Calibration Laboratories & Measurements are traceable to SI Units How we ensure ACCREDITATION Bangladesh BEST Programme

Defined Criteria for Laboratory Accreditation Metrology Laboratory :

Defined Criteria for Laboratory Accreditation Metrology Laboratory Organization Laboratory Quality System Qualified personnel Range of the work capabilities and test methods Laboratory practices and management system Reliable standards and measuring devices Laboratory facilities Adequate measuring capabilities Traceability maintenance Calibration records Satisfactory completion of internal audits Bangladesh BEST Programme

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40 QUALITY SYSTEM ISO/IEC 17025 QUALITY MANUAL PROCEDURE MANUAL METHOD MANUAL FACILITIES MANUAL SAFETY MANUAL Bangladesh BEST Programme

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41 41 ACCREDITED LABORATORY IMPLEMENTATION OF ISO 17025 MANAGEMENT REQUIREMENTS TECHNICAL REQUIREMENTS TRACEABILITY MAINTENANCE OF ENVIRONMENTAL CONDITIONS TRAINED STAFF Bangladesh BEST Programme

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42 42 ENVIRONMENTAL CONDITIONS TEMPERATURE HUMIDITY AIR VELOCITY FREE OF VIBRATION ILLUMINANCE Bangladesh BEST Programme

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43 ACCREDITED MASS LABORATORY ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ± 0.5 0 C , HUMIDITY : 50 ±10% Bangladesh BEST Programme

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44 44 ACCREDITED TEMPERATURE LABORATORY ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ±1 0 C , HUMIDITY : 50 ±10% Bangladesh BEST Programme

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45 ACCREDITED VOLUMETRIC LABORATORY Temperature : 20 ±1 °C Humidity : 60 ±10% Bangladesh BEST Programme

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46 46 CONTENTS OF CALIBRATION CERTIFICATE NAME AND ADDRESS : CUSTOMER/ LABORATORY METHOD CONDITION RECEIVED IDENTIFICATION DATE OF CALIBRATION DATE OF RECALIBRATION ? CALIBRATION RESULTS UNCERTAINTY OF MEASUREMENT TRACEABILITY ENVIRONMENTAL CONDITION Bangladesh BEST Programme

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47 RANGE C.M.C ONE MARK PIPETTE 0 to 200 0.01 GRADUATED PIPETTE 0 to 25 0.001 BURETTE 0 to 200 0.01 VOLUMETRIC FLASK 0 to 2000 0.01 GRADUATED MEASURING CYLINDER 0 to 2000 0.01 SAMPLE OFSCOPE OF ACCREDITATION CALIBRATION mL mL Bangladesh BEST Programme

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48 Accredited Metrology Facilities Industries Products Better Place in Global Market Quality Life Technical Competency ISO Certified QMS Traceable Measurements Ensure Bangladesh BEST Programme

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49 “Calibration of laboratory equipment is important to obtain reliable test results ” Thank you Bangladesh BEST Programme

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