basic concept of measurement - copy

CONCEPTS OF METROLOGY AND IMPORTANCE OF

CALIBRATION

Nihal GunasekaraSri Lanka

Bangladesh BEST Programme

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

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

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”

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

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”

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 )

Units of MeasurementSI 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

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 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.

Expanded Uncertainty

Calculate combined standard uncertainties

Type A

Type B

Exp. Unc. U = Combined Uncertainty X Coverage factor

Ishikawa diagram

Uncertainty of an oven

Calibration (B)

Test oven

Resolution (B)

CJC (B)

Scatter (A)

Digital Thermometer

Resolution (B)

Reference T/C

Confidence Level

Gaussian probability distribution

-kσ +kσ68% Within 1σ of mean95% Within 2σ of mean99% Within 3σ of mean

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” oror

““HOW TO ENSURE THAT HOW TO ENSURE THAT TWO MEASUREMENTS TWO MEASUREMENTS OF THE SAME OF THE SAME

QUANTITIES ARE QUANTITIES ARE COMPATIBLECOMPATIBLE””

How Do We Get Traceability ?

Common point of reference

My laboratory Your laboratory Their laboratory

NMI: The Link Organisation to the International Arena

International standards

National community that is using measurements

National Metrology Institute

HIERACHY OF MEASUREMENT STANDARDS

InstrumentsUsed in Lab/

Industry

Working Standards

Secondary Standards

Primary StandardsTraceable to BIPM

Bangladesh BEST ProgrammeHIERARCHY OF MEASUREMENTS

Metal fixed-point

Number Substances StateDefining temperature

234.3156

273.16

302.9146

429.7485

505.078

692.677

933.473

1234.93

1337.33

1357.77

-38.8344

29.7646

156.5985

231.928

419.527

660.323

961.78

1064.18

1084.62

CALIBRATION HIERARCHY OF MASS STANDARDS

BIPM Kilogram

National Kilogram

Class E1, E2,F1, F2Masses

Analytical &Top loadingPrecisionBalances

OIML M1,M2,M3

Masses

OIML R47

Masses

TRADE MASSES

Platform & Top loading balances

Weighing

Bridges

BIPM Prototype 1kg

EXAMPLE MASS COMPARATOR

Prototype 1kg

Calibrate

Traceable to

Analytical Balance

Transfer

Set of Classes E2, F1, F2, and M1

Traceable to

SI Units

GAUGE BLOCK COMPARATORPrimary Standard

Laser interferometer

Traceable to

Grade K set

Grade 1 set

USECompare

Calibrate

Examples

1. Performance Test on a Incubator at 35 + 0.5 oCSet Temp.

Indicator Value

Measured Mean value

oCMin Max Near

SensorUpper Middle Lower

34.5 34.5 34.6 34.9 34.7 34.5 34.2 0.2

2. Performance Test on a Water Bath at 50 oC

Set Temp.oC

Indicator Value

Measurement

Locations

Measured Mean Value

oCMin Max

48.0 49.5 50.0 C

Uniformity : 0.61 oC

Stability : 0.33 oC

COMPARATOR BALANCES

CLASS E1 1 kg

CLASS E1 SET

CLASS E2 SET

CLASS F1 SET

CLASS F2 SET

CLASS M1 SET

Reference 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 errorManufacture’s 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 & 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

CALIBRATION OF VOLUMETRIC GLASSWARE

FLASKS

CYLINDERS

BURETTES

PIPETTES

ACCURACY CLASSES

CLASS A – Higher grade

CLASS B – Lower grade

Example - Pipettes

Nominal capacity(ml)

Limit of Error (ml)

Class A Class B

METHOD

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

IN-HOUSE PERFORMANCE CHECKS (During Calibration Interval)

ANALYTICAL BALANCES – Using a Calibrated Weight

INCUBATORS - Using a Calibrated Thermocouple

GLASS THERMOMETERS- Ice Point

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

Technical Competence of Calibration Laboratories

& Measurements are

traceable to SI Units

How we ensure

ACCREDITATION

Defined Criteria for Laboratory AccreditationMetrology 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

QUALITY SYSTEM ISO/IEC 17025

QUALITY MANUAL

PROCEDURE MANUAL

METHOD MANUAL

FACILITIES MANUAL

SAFETY MANUAL

ACCREDITED LABORATORY

IMPLEMENTATION OF ISO 17025

MANAGEMENT REQUIREMENTS

TECHNICAL REQUIREMENTS

TRACEABILITY

MAINTENANCE OF ENVIRONMENTAL CONDITIONS

TRAINED STAFF

ENVIRONMENTAL CONDITIONS

TEMPERATURE

HUMIDITY

AIR VELOCITY

FREE OF VIBRATION

ILLUMINANCE

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%

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

RANGE C.M.C

• ONE MARK PIPETTE 0 to 200

•GRADUATED PIPETTE 0 to 25 0.001

•BURETTE 0 to 200

• VOLUMETRIC FLASK 0 to 2000

•GRADUATED MEASURING CYLINDER 0 to 2000 0.01

SAMPLE OFSCOPE OF ACCREDITATION

CALIBRATION

Accredited Metrology Facilities

Industries

Products

Better Place in Global Market

Quality Life

Technical Competency

ISO Certified QMS

Traceable Measurements

Ensure

“Calibration of laboratory equipment is important to obtain reliable test results”

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