CONCEPTS OF METROLOGY AND IMPORTANCE OF CALIBRATION

KEY WORDSCALIBRATION ComparisonMETROLOGY Science of MeasurementTRACEABILITY Unbroken Chain of ComparisonsUNCERTAINTITY Error in MeasurementACCREDITATION Third Party AscertainCALIBRATION INTERVAL Equipment Remains Reliable

**WHAT IS METROLOGY SCIENCE OF MEASUREMENTS

METROLOGY Metrology Covers Three Main Tasks:The definition of internationally accepted units of measurementThe realization of units of measurement by scientific methodEstablishment of traceability chain in documenting the accuracy of a measurement

Metrology is essential in scientific research

CATEGORIES OF METROLOGY Scientific Metrology Development of measurement standardsIndustrial Metrology To ensure the adequate functioning of measurement instruments used in industry, production & testing laboratoriesLegal Metrology or Weights & Measures Accuracy of measurement where these have influence on the transparency of economic transactions, health & safety

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

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.)

* Calibration (Old Definition) Calibration is the comparing of an unknown measurement device against equal or better known standard under specified conditions

CalibrationOperation 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 )

* Units of MeasurementSI Units published by BIPM(Bureau of Weights and Measures)Base UnitsQuantity Unit SymbolLength metre mMass kilogram kgTime second sTemperature kelvin KElectric current ampere ALuminous intensity candela cdAmount of substance mole mol

* Metrology Laboratories Primary Laboratories NML, NMI, NPL etc

Reference Laboratories

Calibration Laboratories

*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 !!!!!

*UncertaintyAn estimate of the possible error in a measurementType A evaluation A series of repeated observations is obtained to determine the standard deviation of the measurement result.Type B evaluationThe evaluation is carried out using available information found in calibration reports, certificates, specifications etc.

* Expanded UncertaintyCalculate combined standard uncertainties Type A Type B

Exp. Unc. U = Combined Uncertainty X Coverage factor

* Ishikawa diagram

Uncertainty of an ovenCalibration (B)Test oven Resolution (B)CJC (B)Scatter (A)Digital ThermometerResolution (B)Reference T/C

* Confidence LevelGaussian probability distribution -k +k68%Within 1 of mean95%Within 2 of mean99%Within 3 of mean

* Metrological Traceabilityproperty 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

** How Do We Get Traceability ? Common point of reference

My laboratoryYour laboratoryTheir laboratory

**NMI: The Link Organisation to the International ArenaInternational standards National community that is using measurementsNational Metrology Institute

HIERACHY OF MEASUREMENT STANDARDSInstrumentsUsed in Lab/ IndustryWorking Standards Secondary Standards Primary StandardsTraceable to BIPM HIERARCHY OF MEASUREMENTS

* Metal fixed-point

NumberSubstancesStateDefining temperatureKoC123456789HgH20GaInSnZnAlAgAuCuTTMFFFFFFF234.3156273.16302.9146429.7485505.078692.677933.4731234.931337.331357.77-38.83440.0129.7646156.5985231.928419.527660.323961.781064.181084.62

* CALIBRATION HIERARCHY OF MASS STANDARDS

**BIPM Prototype 1kg

*GAUGE BLOCK COMPARATORPrimary Standard Laser interferometer Traceable to Grade K set Grade 1 set USECompareCalibrate

* Examples 1. Performance Test on a Incubator at 35 + 0.5 oC

Set Temp.oCIndicator ValueoCMeasured Mean valueoCExpanded UncertaintyoC

MinMaxNear SensorUpperMiddleLower34.534.534.634.934.734.534.2 0.2

*2. Performance Test on a Water Bath at 50 oCUniformity : 0.61 oCStability : 0.33 oC

Set Temp.oCIndicator ValueoCMeasurementLocationsMeasured Mean ValueExpanded UncertaintyoCMinMax48.049.550.0CPQRS50.150.250.150.150.0

1

*COMPARATOR BALANCESCLASS E1 1 kgCLASS E1 SETCLASS E2 SETCLASS F1 SETCLASS F2 SETCLASS M1 SETMASSReference and Auxiliary Equipment

* 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

* CALBRATION INTERVALS ISO 17025 Requirements:

Capable of achieving required accuracyComply with specifications relevant to test/calibration methodUse under established calibration programme

Therefore need to :

Define required accuracyIdentify the equipment that can affect itManage all equipment under a calibration programme

* RECOMMENDED CALBRATION INTERVALS N No single correct answer Calibration represents an instantaneous snapshot of actual condition Depend upon

Level of stress - subjectedStability of past calibrationAllowable tolerance rangeRequired accuracyQuality Assurance Requirements

* RECOMMENDED CALBRATION INTERVALS Final Analysis Period between two calibrations Determined & Monitored

USER HIMSELF

* HOW TO ESTABLISH CALIBRATION INTERVAL

Consider influencing factors and existing knowledge : eg

Accuracy sought & consequences of errorManufactures recommendationsAccommodation & environmentPurpose and usageMaintenance & servicingTrends from previous calibrationFrequency of checksEtc. etc. etc. .

Ref. - ILAC G 24 : Guidelines for determination of calibration interval of measuring instruments

** RECOMMENDED PRACTICES Calibration at (planned) periodic intervals to ensure acceptable accuracy & reliabilityShorten the intervals when results of previous calibration suggest itMay lengthen intervals on basis of demonstrated performanceDocumented procedure for assigning and adjusting calibration intervalsFully documented re-calibration system

*CALIBRATION OF VOLUMETRIC GLASSWARE FLASKSCYLINDERSBURETTESPIPETTESACCURACY CLASSES CLASS A Higher gradeCLASS B Lower grade

*Example - PipettesMETHOD

Gravimetric Method IS0 4787 -2010(Laboratory Glassware- Volumetric instruments- Method of Testing of capacity and for use)

Nominal capacity(ml)Limit of Error (ml)Class AClass B1251002000.0080.030.080.10.0150.060.150.2

* IN-HOUSE PERFORMANCE CHECKS (During Calibration Interval)ANALYTICAL BALANCES Using a Calibrated WeightINCUBATORS - Using a Calibrated ThermocoupleGLASS THERMOMETERS- Ice Point

** Importance of Calibration Assurance of accurate of measurementsAbility to trace measurements to International standardsInternational acceptance of test/calibration reportsCorrect diagnosis of illness (medical reports)Consumer protection (legal metrology)Meeting the requirements of ISO 9000 and 17025

*Technical Competence of Calibration Laboratories& Measurements are traceable to SI Units How we ensure

Defined Criteria for Laboratory AccreditationMetrology Laboratory

OrganizationLaboratory Quality System Qualified personnelRange of the work capabilities and test methodsLaboratory practices and management systemReliable standards and measuring devicesLaboratory facilitiesAdequate measuring capabilitiesTraceability maintenanceCalibration recordsSatisfactory completion of internal audits

*QUALITY SYSTEM ISO/IEC 17025QUALITY MANUALPROCEDURE MANUALMETHOD MANUALFACILITIES MANUALSAFETY MANUAL

** ACCREDITED LABORATORYIMPLEMENTATION OF ISO 17025MANAGEMENT REQUIREMENTSTECHNICAL REQUIREMENTSTRACEABILITY MAINTENANCE OF ENVIRONMENTAL CONDITIONSTRAINED STAFF

**ENVIRONMENTAL CONDITIONSTEMPERATUREHUMIDITYAIR VELOCITYFREE OF VIBRATIONILLUMINANCE

*ACCREDITED MASS LABORATORY ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 0.5 0C , HUMIDITY : 50 10%

** ACCREDITED TEMPERATURE LABORATORY ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 1 0C , HUMIDITY : 50 10%

* ACCREDITED VOLUMETRIC LABORATORYTemperature : 20 1 C Humidity : 60 10%

**CONTENTS OF CALIBRATION CERTIFICATENAME AND ADDRESS :CUSTOMER/ LABORATORYMETHODCONDITION RECEIVEDIDENTIFICATIONDATE OF CALIBRATIONDATE OF RECALIBRATION ?CALIBRATION RESULTSUNCERTAINTY OF MEASUREMENTTRACEABILITYENVIRONMENTAL CONDITION

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*Accredited Metrology FacilitiesIndustries ProductsBetter Place in Global MarketQuality LifeTechnical CompetencyISO Certified QMS Traceable MeasurementsEnsure

*Calibration of laboratory equipment is important to obtain reliable test results

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