Bangladesh BEST Programme
CONCEPTS OF METROLOGY AND IMPORTANCE OF
CALIBRATION
Nihal Gunasekara
Sri 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
Bangladesh BEST Programme
WHAT IS METROLOGY
SCIENCE OF MEASUREMENTS
Everything has
to do with
measurement
Experiment
or test
Designing
Conducting
Analyzing Results
CAN BE SEEN
EVERYWHERE
Allowing people
to plan their lives
and make
commercial
exchange with
confidence
within the Metrology realm
3
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.)
Bangladesh BEST Programme
Calibration (Old Definition)
“Calibration
is the comparing of an unknown
measurement device against equal or better
known standard under specified conditions”
8
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 )
Bangladesh BEST Programme
Units of Measurement
SI Units published by BIPM(Bureau of Weights and Measures)
Base Units…
Quantity
Unit
Length
metre
m
Mass
kilogram
kg
Time
second
s
Temperature
kelvin
K
Electric current
ampere
A
Luminous intensity
candela
cd
Amount of substance mole
Symbol
mol
10
Bangladesh BEST Programme
Metrology Laboratories
 Primary Laboratories NML, NMI, NPL etc
 Reference Laboratories
 Calibration Laboratories
11
Bangladesh BEST Programme
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 !!!!!
12
Bangladesh BEST Programme
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.
13
Bangladesh BEST Programme
Expanded Uncertainty
Calculate combined standard uncertainties
Type A
Type B
Exp. Unc. U = Combined Uncertainty X Coverage factor
14
Bangladesh BEST Programme
Ishikawa diagram
Reference T/C
Calibration (B)
Digital
Thermometer
Resolution (B)
Scatter (A)
CJC (B)
Uncertainty
of an oven
Test oven
Resolution (B)
15
Bangladesh BEST Programme
Confidence Level
Gaussian probability distribution
68%
95%
99%
-kσ

+kσ
Within 1σ of mean
Within 2σ of mean
Within 3σ of mean
16
Bangladesh BEST Programme
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”
17
Bangladesh BEST Programme
How Do We Get Traceability ?
Common point of reference
My laboratory
Your laboratory
Their laboratory
18
Bangladesh BEST Programme
NMI: The Link Organisation to the International Arena
International standards
National Metrology Institute
National community that is using
measurements
19
HIERACHY OF MEASUREMENT STANDARDS
Bangladesh BEST Programme
HIERARCHY OF MEASUREMENTS
Primary Standards
Traceable to BIPM
Secondary
Standards
Working
Standards
Instruments
Used in Lab/
Industry
Bangladesh BEST Programme
Metal fixed-point
Number
Substances
State
Hg
1
Defining temperature
K
oC
T
234.3156
-38.8344
H20
T
273.16
0.01
2
Ga
M
302.9146
29.7646
3
In
F
429.7485
156.5985
4
Sn
F
505.078
231.928
5
Zn
F
692.677
419.527
6
Al
F
933.473
660.323
7
Ag
F
1234.93
961.78
8
Au
F
1337.33
1064.18
9
Cu
F
1357.77
1084.62
21
Bangladesh BEST Programme
CALIBRATION HIERARCHY OF MASS STANDARDS
BIPM Kilogram
National Kilogram
Class E1, E2,F1, F2
Masses
OIML
M1,M2,M3
OIML R47
Masses
Masses
Analytical &Top loading
Precision
Balances
TRADE
MASSES
Platform & Top
loading balances
Weighing
Bridges
22
Bangladesh BEST Programme
EXAMPLE
MASS COMPARATOR
Traceable to
BIPM Prototype 1kg
USE
Transfer
Prototype 1kg
Traceable
to
SI Units
Calibrate
Analytical Balance
Set of Classes E2, F1, F2, and M1
23
Bangladesh BEST Programme
GAUGE BLOCK COMPARATOR
Primary Standard
Traceable to
Laser interferometer
Compare
USE
Grade K set
Calibrate
Grade 1 set
24
Bangladesh BEST Programme
Examples
1. Performance Test on a Incubator at 35 + 0.5 oC
Set Temp.
Indicator Value
oC
oC
34.5
Expanded
Uncertainty
Measured Mean value
oC
oC
Min
Max
Near
Sensor
Upper
Middle
Lower
34.5
34.6
34.9
34.7
34.5
34.2
 0.2
25
Bangladesh BEST Programme
2. Performance Test on a Water Bath at 50 oC
Set Temp.
Indicator Value
Measurement
oC
oC
Locations
48.0
S
P
C
R
Q
Min
Max
49.5
50.0
Measured
Mean
Value
C
50.1
P
50.2
Q
50.1
R
50.1
S
50.0
Expanded
Uncertainty
oC
1
Uniformity : 0.61 oC
Stability
: 0.33 oC
26
Bangladesh BEST Programme
MASS
Reference and Auxiliary Equipment
 COMPARATOR BALANCES
 CLASS E1 1 kg





CLASS
CLASS
CLASS
CLASS
CLASS
E1 SET
E2 SET
F1 SET
F2 SET
M1 SET
27
Bangladesh BEST Programme
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
28
Bangladesh BEST Programme
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
29
Bangladesh BEST Programme
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
30
Bangladesh BEST Programme
RECOMMENDED CALBRATION INTERVALS
Final Analysis
Period between two calibrations
Determined & Monitored
USER HIMSELF
31
Bangladesh BEST Programme
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
32
Bangladesh BEST Programme
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
33
Bangladesh BEST Programme
CALIBRATION OF VOLUMETRIC GLASSWARE

FLASKS

CYLINDERS

BURETTES

PIPETTES
ACCURACY CLASSES
CLASS A – Higher grade
CLASS B – Lower grade
34
Bangladesh BEST Programme
Example - Pipettes
Nominal
capacity(ml)
Limit of Error (ml)
Class A
Class B
1
0.008
0.015
25
0.03
0.06
100
0.08
0.15
200
0.1
0.2
METHOD
Gravimetric Method – IS0 4787 -2010
(Laboratory Glassware- Volumetric instruments- Method of
Testing of capacity and for use)
35
Bangladesh BEST Programme
IN-HOUSE PERFORMANCE CHECKS
(During Calibration Interval)
 ANALYTICAL BALANCES – Using a Calibrated
Weight
 INCUBATORS -
Using a Calibrated
Thermocouple
 GLASS THERMOMETERS- Ice Point
36
Bangladesh BEST Programme
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
37
Bangladesh BEST Programme
How we ensure
Technical Competence of
Calibration Laboratories
&
Measurements are
traceable to SI Units
ACCREDITATION
38
Bangladesh BEST Programme
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
QUALITY SYSTEM ISO/IEC 17025
 QUALITY MANUAL
 PROCEDURE MANUAL
 METHOD MANUAL
 FACILITIES MANUAL
 SAFETY MANUAL
40
Bangladesh BEST Programme
ACCREDITED LABORATORY
 IMPLEMENTATION OF ISO 17025
MANAGEMENT REQUIREMENTS
TECHNICAL REQUIREMENTS
 TRACEABILITY
 MAINTENANCE OF ENVIRONMENTAL CONDITIONS
 TRAINED STAFF
41
Bangladesh BEST Programme
ENVIRONMENTAL CONDITIONS
TEMPERATURE
HUMIDITY
AIR VELOCITY
FREE OF VIBRATION
ILLUMINANCE
42
Bangladesh BEST Programme
ACCREDITED MASS LABORATORY
ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ± 0.5 0C , HUMIDITY : 50 ±10%
43
Bangladesh BEST Programme
ACCREDITED TEMPERATURE LABORATORY
ENVIRONMENTAL CONDITIONS: TEMPERATURE: 23 ±1 0C , HUMIDITY : 50 ±10%
44
Bangladesh BEST Programme
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
46
Bangladesh BEST Programme
SAMPLE OFSCOPE OF ACCREDITATION
CALIBRATION
RANGE
mL
C.M.C
mL
• 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
47
Bangladesh BEST Programme
Accredited Metrology
Facilities
Ensure
Traceable Measurements
Technical Competency
Better Place in
Global Market
Industries
ISO Certified QMS
Products
Quality
Life
48
Bangladesh BEST Programme
“Calibration of
laboratory equipment
is important to obtain
reliable test results”
49