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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
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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
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
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
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
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.)
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Calibration (Old Definition)
“Calibration is the comparing of an unknown measurement device against equal or better known standard under specified conditions”
Bangladesh BEST Programme
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 )
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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
Bangladesh BEST Programme
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Metrology Laboratories
Primary Laboratories NML, NMI, NPL etc
Reference Laboratories
Calibration Laboratories
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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 !!!!!
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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.
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Expanded Uncertainty
Calculate combined standard uncertainties
Type A
Type B
Exp. Unc. U = Combined Uncertainty X Coverage factor
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Ishikawa diagram
Uncertainty of an oven
Calibration (B)
Test oven
Resolution (B)
CJC (B)
Scatter (A)
Digital Thermometer
Resolution (B)
Reference T/C
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Confidence Level
Gaussian probability distribution
-kσ +kσ68% Within 1σ of mean95% Within 2σ of mean99% Within 3σ of mean
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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””
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How Do We Get Traceability ?
Common point of reference
My laboratory Your laboratory Their laboratory
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NMI: The Link Organisation to the International Arena
International standards
National community that is using measurements
National Metrology Institute
Bangladesh BEST Programme
HIERACHY OF MEASUREMENT STANDARDS
InstrumentsUsed in Lab/
Industry
Working Standards
Secondary Standards
Primary StandardsTraceable to BIPM
Bangladesh BEST ProgrammeHIERARCHY OF MEASUREMENTS
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Metal fixed-point
Number Substances StateDefining temperature
K oC
1
2
3
4
5
6
7
8
9
Hg
H20
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
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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
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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
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GAUGE BLOCK COMPARATORPrimary Standard
Laser interferometer
Traceable to
Grade K set
Grade 1 set
USECompare
Calibrate
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Examples
1. Performance Test on a Incubator at 35 + 0.5 oCSet Temp.
oC
Indicator Value
oC
Measured Mean value
oC
Expanded Uncertainty
oCMin Max Near
SensorUpper Middle Lower
34.5 34.5 34.6 34.9 34.7 34.5 34.2 0.2
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2. Performance Test on a Water Bath at 50 oC
SPC
R
Q
Set Temp.oC
Indicator Value
oC
Measurement
Locations
Measured Mean Value
Expanded Uncertainty
oCMin 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 oC
Stability : 0.33 oC
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COMPARATOR BALANCES
CLASS E1 1 kg
CLASS E1 SET
CLASS E2 SET
CLASS F1 SET
CLASS F2 SET
CLASS M1 SET
MASS
Reference and Auxiliary Equipment
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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
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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
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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
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RECOMMENDED CALBRATION INTERVALS
Final Analysis Period between two calibrations
Determined & Monitored
USER HIMSELF
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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
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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
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CALIBRATION OF VOLUMETRIC GLASSWARE
FLASKS
CYLINDERS
BURETTES
PIPETTES
ACCURACY CLASSES
CLASS A – Higher grade
CLASS B – Lower grade
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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)
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IN-HOUSE PERFORMANCE CHECKS (During Calibration Interval)
ANALYTICAL BALANCES – Using a Calibrated Weight
INCUBATORS - Using a Calibrated Thermocouple
GLASS THERMOMETERS- Ice Point
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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
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Technical Competence of Calibration Laboratories
& Measurements are
traceable to SI Units
How we ensure
ACCREDITATION
Bangladesh BEST Programme
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
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QUALITY SYSTEM ISO/IEC 17025
QUALITY MANUAL
PROCEDURE MANUAL
METHOD MANUAL
FACILITIES MANUAL
SAFETY MANUAL
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ACCREDITED LABORATORY
IMPLEMENTATION OF ISO 17025
MANAGEMENT REQUIREMENTS
TECHNICAL REQUIREMENTS
TRACEABILITY
MAINTENANCE OF ENVIRONMENTAL CONDITIONS
TRAINED STAFF
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ENVIRONMENTAL CONDITIONS
TEMPERATURE
HUMIDITY
AIR VELOCITY
FREE OF VIBRATION
ILLUMINANCE
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ACCREDITED MASS LABORATORY
ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ± 0.5 0C , HUMIDITY : 50 ±10%
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ACCREDITED TEMPERATURE LABORATORY
ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ±1 0C , HUMIDITY : 50 ±10%
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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
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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
mLmL
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Accredited Metrology Facilities
Industries
Products
Better Place in Global Market
Quality Life
Technical Competency
ISO Certified QMS
Traceable Measurements
Ensure
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“Calibration of laboratory equipment is important to obtain reliable test results”
Bangladesh BEST Programme
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