Basics of Metrology

1. UNIT-I BASICS OF METROLOGY
Introduction to metrology-Need-
Element Work piece, Instruments-
Persons-Environment-Their effect on
precision and accuracy-Errors-Errors in
measurement-Types-Control-Types of
standards.
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2. INTRODUCTION TO METROLOGY
• Science of measurement
• Ensuring uniformity of measurement
• Developing new methods of measurement
• Analyzing new methods
• Gauges design, manufacturing and testing
• Changing units in the form of standards
• Researching cases and industrial inspection
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3. INTRODUCTION TO METROLOGY
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4. NEED FOR METROLOGY
• To determine true dimensions
• To ensure public health and human safety
• To evaluate the performance of a system
• To study the basic laws of nature
• To check the limitations of theory in practical
situation
• To design and finding new data
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5. METHODS OF MEASUREMENT
• Direct comparison (length, mass. time)
Primary measurement
Secondary measurement (single
conversion)
Tertiary measurement (more than one
conversion)
• Indirect comparison
• Comparative (using comparators)
mechanical, electrical, hydraulic, pneumatic
types
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6. METHODS OF MEASUREMENT
• Coincidence (Certain Values and signals)
• Fundamental
• Contact ( Sensor and Measuring tip)
• Transposition
• Complementary (Volume determination)
• Deflection (pressure measurement)
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7. Direct Method
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8. 1. Primary sensing element (receives energy as
input signal)
2. Variable conversion element (without
changing)
3. Variable manipulation element (magnification)
4. Data transmission element (transmit from one
element to other)
5. Data processing element (modify the data
before displayed)
6. Data presentation element (monitoring)
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GENERALIZED MEASURING ELEMENT
SYSTEM

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10. BOURDON TUBE PRESSURE GAUGE
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11. UNITS
• M.K.S,CGS &S.I
• System International
Fundamental units-Length, Mass, Time,
Temperature, Electric current & Luminus
intensity.
Supplementary units-radian, steradian
Derived units-A,V,Density,v,a,F,P,W,p
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12. STANDARD
• Physical representation of unit of
measurement
• The term standard is used to denote
universally accepted specifications for devices.
• Components or processes which ensure
conformity and interchangeability throughout
a particular industry.
• A standard provides a reference for assigning a
numerical value to a measured quantity.
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13. TYPES OF STANDARD
• International standards (Internationally
accepted)
• Primary standards ( National Physical
Laboratory at New Delhi)
• Secondary standards(Basic reference
standard)
• Working standards(To check the components)
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14. Measuring Instruments
• Deflection and null type
• Analog and Digital Instruments
• Active and passive type instruments
• Automatic and Manually operated instrument
• Absolute and secondary instruments
(Galvanometer)
• Contacting and non- contacting instruments
• Intelligent instrument (Remote operated)
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15. DEFLECTION TYPE COINCEDENCE
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16. TRANSPOSITION METHOD
CONTACT METHOD
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17. ACCURACY
• The degree of closeness of a measurement compared
to the expected value is known as accuracy.
• It refers how closely the measured value agrees with
the true value.
• Accuracy as “Percentage of Full Scale Reading”:
In case of Instruments having Uniform scale
Percentage of Full Scale Reading=Measured value-
True value/Maximum Scale Value
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18. Accuracy (Cont….)
• Accuracy as “Percentage of True Value”
It is way of specifying the accuracy.
True value of quantity to be measured.
Percentage of True Value=Measured value-True value/True
value
• Accuracy as “Percentage of scale span”:
• qmax=Maximum point sacle is calibrated
• qmin=Minimum scale reading
• qmax-qmin=Scale span
Example:±0.1%-Accuracy
Range-10 to 150 units
Scale Span=±0.1(150-10)/100=±0.14 uints errors
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19. Precision
• Precision is the degree of exactness for which an
instruments is designed or intended to perform.
• It refers the repeatability or consistency of
measurements.
• They have two characteristics:
• i).Conformity ii).Significant Figures
• Conformity:There are no deviations from observed
value,the error created by the limitation of the scale
reading is called as precision error.
• Example:2834267Ώ
• Multimeter indicates 2.8M Ώ
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20. PRECISION
• Significant Figure: It Conveys the actual information
regarding the magnitude and the measurement
precision of a quantity.
• Significant figure is the number of digits for
measuring output
• Example:Voltage 240V
• Closer valve 240V or 239V or 241V (3 Values)
• Significant figure 240.0V or 239.9V or 240.1V
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21. Accuracy Vs Precision
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22. Accuracy Vs Precision
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23. Accuracy Vs Precision
• Example:100Mpa with Pressure Gauge
• Six Readings are taken
103,104,102,103,102,104 Mpa
• Average 103,Max Deviation ±1 Mpa
• Instrument Calibrated ±1 Mpa.
• Accuracy(104-100/100)=4%
• Precision ±1%
• High Precision Poor Accuracy
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24. Accuracy Vs Precision
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25. Persons and Environment
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26. SENSITIVITY
• Is Defined as the ratio
of magnitude of output
Signal to the magnitude
of input signal.
• Input-output relation is
linear means Constant
for all values of input.
• Non-Linear means
instruments depends
on the value of the
input quality.
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27. SENSITIVITY
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• Sensitivity has no
unique unit.
• Which is dependent on
the instrument.
• Some of units of
sensitivity millimeter
per micro-
ampere,millimeter per
ohm,counts per
volt,ohms per degrees
celsius.

28. SENSITIVITY
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Problems on sensitivity

30. Problems on sensitivity
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31. Problems on sensitivity
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32. Stability
• The ability of a measuring instrument to retain
its calibration over a long period of time is
called stability.
• Stability is the key to predictability.
• Used to determined by control chart.
• Repeated measurements are taken by
instruments.
• Measurement system robust to the condition.
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33. READABILITY
• Readability is defined as the closeness with
which the scale of analog instrument can be
read.
• Present Days Industry are preferred digital type
instrument not analog instruments.
• Readability depends on both the instruments
and observer
• Examples: Weighing Scale, Thermometer
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34. STABILITY AND READABILITY
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35. REPEATABILITY
• Repeatability is defined
as the closeness of
agreement among the
number of consecutive
measurement of the
output for the same
value of input under the
same operating
conditions.
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36. REPEATABILITY
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• In diagram shows input and output
relationship curve with positive and negative
reputability.
Reproducibility: Reproducibility is defined as the
closeness of agreement among repeated
measurements measurement of the output
for the same value of input under the same
operating conditions over a period of time.

37. Reproducibility
• Reproducibility and repeatability are the
measures of the closeness to a given input
may be measured again and again.
• Reproducibility defined two terms:
(i).Stability-Comapred to the time taken for
reading the measurement
(ii).Constancy-Constant input testedmesurement
are allowed to vary within the specified limits.
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38. ERRORS
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Difference between the measured value and true value
True absolute error:
It is the algebraic difference between the result of
measurement and the conventional true value of the quantity
measured.
Apparent absolute error:
If the series of measurement are made then the algebraic
difference between one of the results of measurement and
the arithmetical mean is known as apparent absolute error.

39. ABSOLUTE
APPARENT
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40. Relative Errors
• Relative errors is defined as the results of the
absolute error and the value of comparision
used for the calculation of absolute error.
• Comparison may be true value or
conventional true value or arithmetic mean
for series for measurement.
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41. TYPES OF ERRORS
• STATIC ERROR
Characteristic error
Reading error
Environmental error
• LOADING ERROR
• DYNAMIC ERROR
Systematic error
i) Calibration errors
ii) Ambient or Atmospheric conditions
iii) Avoidable Error
iv) stylus pressure
Random error
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42. stylus pressure
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43. Problems on Errors
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44. Problems on Errors
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45. Problems on Errors
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46. Problems on Errors
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47. LIMITS AND TOLORANCES
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49. Correction and Calibration
• Correction is defined as a value which is added
algebraically to the uncorrected result of
measurement to compensate for an assumed
systematic error.
• Calibration is the process of determining and
adjusting an instruments accuracy to make
sure its accuracy is within the manufactures
specifications.
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50. CALIBRATION
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51. Questions?
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