Engineering Metrology 20-21
Chapter 01
Introduction to Metrology
Metrology
“Metrology is Science Of Measurement and is primarily concerned with the
establishment, conservation, and transfer of units of measurements and their
standards.”
Metrology Needs precise measurement and use of apparatus and equipment to
obtain high degree of accuracy.
It is also related with analysis of accuracy and methods related to error.
Objectives Of Metrology:
It Can be used for selection of proper measuring instrument in
industries.
It Can be used for deciding proper measuring standards.
It is used for minimizing cost of inspection.
For determining process capabilities.
To decide and find out tolerances.
To achieve standardization.
To maintain accuracy.
To maintain precision.
Types Of Metrology:
1. Legal Metrology
2. Scientific Metrology
3. Deterministic Metrology
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1) Legal Metrology:
Metrology which relates units of measurements, methods, of
measurements and technical and legal needs.
Legal metrology directed by organization like National service
of legal Metrology (NSLM) .
They also ensure the guarantee of their accuracy by
comparison with international standards.
Legal Metrology plays very important role in maintaining
uniformity of measurement throught the word with the help of
International Organization of Weight and Measure (IOWM) and
NSLM.
Application Of Legal Metrology:
For commercial Transaction.
Industrial Measurements And Accuracy.
Measurement Of Health
Measurement For Human Safety.
2) Scientific Metrology:
Scientific metrology is related to development of new Measuring
methodology and scientific Methods.
It is used for validate the theories.
3) Deterministic Metrology:
Deterministic metrology is that in which part of replaced by
process measurement.
It is useful for machines under automatic control.
Use of automatic sensors is there.
Used for very high precision manufacturing machines.
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Industrial Metrology:
Industrial metrology is the industry related development of
inspection for specific industrial need.
Inspection:
Inspection defined as checking of quality characteristics of given
job.
Need Of Inspection:
Inspection is essential in any manufacturing process for folloeing
purpose.
1. To achieve Quality Output.
2. To Adopt change in Technology.
3. For Mass production.
4. To Save money
5. To obtain Interchangeability.
6. To develop reputation.
Instrument:
An instrument is the device which senses a physical parameter
,process and translates it in to a format which can be interpreted by
the observer.
Desirable Qualities of an ideal Instrument:
It should be accurate and sensitive.
Should posses sufficient Strength.
It should be safe for operation.
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Display output Clearly.
Should Have low cost.
Should have low maintenance.
Reliable.
Factors Affecting on accuracy of an instrument.
1. Make of Instrument.
2. Calibration of instrument.
3. Handling of Instrument.
4. Proper Method of using an Instrument.
5. Reading taken Style of an Instrument.
6. Environmental Conditions.
Accuracy:
Accuracy of an instrument is closeness to an accepted value(
Standard).
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Precision:
Precision is defined as repeatability of measuring process.
It is set of measurements.
Difference between accuracy and precision:( Very
IMP)
Sr.No. Accuracy Precision
Degree of closeness of the It represents repeatability of
01
measured value to true value. measurement process.
Measurement are dependent Measurement are dependent
02
on the systematic error on the random error.
Determined by proper Determined by statically
03
calibration analysis
Accuracy is alleyways Precision may not accurate.
04
precise.
05
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Reliability:
The reliability of an instrument is defined as the possibility
that it will perform its assigned functions for a specific period of
time under given conditions.
Calibration:
Calibration is the process of establishing the reliability of
measuring instrument.
OR
Calibration is the comparison of instrument with
predetermined standards.
Importance/Need OF instrument calibration:
It is the Result of Quantitative calibration.
Calibration improves accuracy.
Calibration improves Reliability.
Calibration can set secondary Standard.
Calibration can reduce error.
Calibration can is imp in MQC lab.
Sensitivity:
It is defined as ratio of ability of an instrument to detect a
small variations in a quantity being measured.
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Response Time:
Time which passes after the sudden changes in the measured
quantity until instrument give an indication.
Repeatability:
It is the property of instrument to give the same output value
each time the measurement of a given quantity is repeated under
the same conditions.
Interchangeability:
It is defined as the ability to interchange various parts of an
assembly at the time of assembling or replacing.
Example: A spark plug replacement of motorcycle.
Now a days production of various components are done at
different places .And assembled at different places.
Also to cope up the mass production demand
interchangeability is very important.
Advantages Of Interchangeability:
Easy to manufacture in mass production.
Easy to replacement of parts.
Less Cost of manufacturing.
Ease of Maintenance.
Reproducibility:
Reproducibility of measurement is the quantitative measure of
the closeness of the agreement between the results of
measurements pf the same mesrand carried out by changing
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the method of measurement observer measuring instrument,
location ,condition of use time etc.
Readability:
It is the ability of measurement so that it will be giving
easiness to read the reading of an instrument.
Traceability:
It is the ability of to identify an instrument , the operator and
flow process line of the job for find out the errors during
manufacturing process.
Error:
Error is defined as the difference between the true value and
measured value of the given job during measurement is called
as error.
Sources Of Error:
Following are the primary sources of error.
Adjustment of error
Faulty Instrument
Method of location of instrument.
Environmental Effects.
Error Because of properties of object.
Error due to surface finish of object.
Error due to change in size of object.
Observational Error.
Error cause by measuring forces of an instrument.
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Types Of Error:
Systematic Error
Random Error
Temperature/ Environmental Error
Dirt Error
Support Error
Contact Pressure Error
Contact Pressure.
Systematic Error:
The systematic error are in the form of experimental mistakes.
These are controllable in magnitude and sense.
These error have definet value.
e.g. Calibration Error, Ambient condition Error, stylus
pressure error, Experimental arrangement error.
Random error:
These type of error are occur randomly.
They can not be determined.
Generated due to large no of unpredictable reason.
e.g operator error. Fluctuations of instrument.
Abbes Principal Of Alignment:
It state that the axis or line of measurement of the measured
part should coincide with the measuring scale or the axis of
measurement of the measuring instrument.
Note: If abbes principal is not followed cosine error may be
developed.
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Difference Between Systematic Error And Random Error
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Selection of Instrument:
Following factors are considered while selection of instrument.
Range of Instrument.
Scale Spacing Of Instrument.
Sensitivity Of Instrument.
Reading Accuracy of Instrument.
Precision Of Instrument.
Effect of environmental Condition on Instrument.
Cost Of Instrument.
Requirement of Customer.
Need of Calibration.
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