1. Definition
Metrology is the name given to the science of pure measurement.
Engineering Metrology is restricted to measurements of length & angle
Measurement is defined as the process of numerical evaluation of a dimension or the process of comparison with standard measuring instruments

2. Need of Measurement Establish standard Interchangeability
Customer Satisfaction
Validate the design
Physical parameter into meaningful number
True dimension
Evaluate the Performance

3. Methods of Measurement
Direct method
Indirect method
Comparative method
Coincidence method
Contact method
Deflection method
Complementary method

4. Direct method Measurements are directly obtained
 Ex: Vernier Caliper, Scales

5. Indirect method Obtained by measuring other quantities
Ex : Weight = Length x Breadth x Height x Density

6. Comparative Method It’s compared with other known value
 Ex: Comparators

7. Coincidence method
Measurements coincide with certain lines and signals
Fundamental method
Measuring a quantity directly in related with the definition of that quantity
Contact method
Sensor/Measuring tip touch the surface area

8. Complementary method
The value of quantity to be measured is combined with known value of the same quantity
Ex:Volume determination by liquid displacement

9. Deflection method
The value to be measured is directly indicated by a deflection of pointer
Ex: Pressure Measurement

10. Common elements of Generalized measuring system
Primary sensing element
Variable conversion element
Variable manipulation element
Data transmission element
Data processing element
Data presentation element

11. Primary sensing element Variable conversion element
Variable manipulation element
Temperature
Data transmission element
Observer
Data presentation element
Data processing element

12. Units and standards SI: fundamental Units
Physical Quantity
Unit Name
Symbol
length
meter m
mass
kilogram kg
time
second s
electric current
ampere A
temperature
Kelvin K
amount of substance
mole
mol
luminous intensity
candela cd

13. SI: Derived Units area square meter m2 volume cubic meter m3 speed
Physical Quantity
Unit Name
Symbol
area
square meter m2
volume
cubic meter m3
speed
meter per
second
m/s
acceleration
second squared
m/s2
weight, force
newton N
pressure
pascal Pa
energy, work
joule J

14. Supplementary units Plane angle Radian Solid angle Steradian
Physical Quantity
Unit Name
Symbol
Plane angle
Radian
rad
Solid angle
Steradian sr

15. Standards International standards Primary standards
Secondary standards
Working standards

16. Measuring Instruments
Deflection and null type instruments
Analog and digital instruments
Active and passive instruments
Automatic and manually operated instruments
Contacting and non contacting instruments
Absolute and secondary instruments
Intelligent instruments.

17. DEFLECTION AND NULL TYPE
Physical effect generated by the measuring quantity
Equivalent opposing effect to nullify the physical effect caused by the quantity

18. ANALOG AND DIGITAL INSTRUMENTS
Physical variables of interest in the form of continuous or stepless variations
Physical variables are represented by digital quantities

19. ACTIVE AND PASSIVE INSTRUMENTS
Instruments are those that require some source of auxiliary power
The energy requirements of the instruments are met entirely from the input signal

20. Automatic and manually operated
Manually operated – requires the service of human operator
Automated – doesn't requires human operator

21. Contacting And Non Contacting Instruments
A contacting with measuring medium
Measure the desired input even though they are not in close contact with the measuring medium

22. Absolute and Secondary Instruments
These instruments give the value of the electrical quantity in terms of absolute quantities
Deflection of the instruments can read directly
A galvanometer is a type of ammeter: an instrument for detecting and measuring electric current. It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.

23. Intelligent instruments
Microprocessors are incorporated with measuring instruments

24. Characteristics of Measuring Instrument
Sensitivity
Readability
Range of accuracy
Precision

25. Definition
Sensitivity- Sensitivity is defined as the ratio of the magnitude of response (output signal) to the magnitude of the quantity being measured (input signal)
Readability- Readability is defined as the closeness with which the scale of the analog instrument can be read

26. Definition
Range of accuracy- Accuracy of a measuring system is defined as the closeness of the instrument output to the true value of the measured quantity
Precision- Precision is defined as the ability of the instrument to reproduce a certain set of readings within a given accuracy

27. Sensitivity
If the calibration curve is liner, as shown, the sensitivity of the instrument is the slope of the calibration curve.
If the calibration curve is not linear as shown, then the sensitivity varies with the input.

28. Sensitivity
This is the relationship between a change in the output reading for a given change of the input. (This relationship may be linear or non-linear.)
Sensitivity is often known as scale factor or instrument magnification and an instrument with a large sensitivity (scale factor) will indicate a large movement of the indicator for a small input change.

29. Readability
Readability is defined as the ease with which readings may be taken with an instrument.
Readability difficulties may often occur due to parallax errors when an observer is noting the position of a pointer on a calibrated scale

30. Accuracy
Accuracy = the extent to which a measured value agrees with a true value
The difference between the measured value & the true value is known as ‘Error of measurement’
Accuracy is the quality of conformity

31. Precision
The precision of a measurement depends on the instrument used to measure it.
For example, how long is this block?

32. Accuracy vs. Precision High Accuracy High Precision High Precision
Low Accuracy

33. Uncertainty
The word uncertainty casts a doubt about the exactness of the measurement results
True value = Estimated value + Uncertainty

34. Performance of Instruments
All instrumentation systems are characterized by the system characteristics or system response
There are two basic characteristics of Measuring instruments, they are
Static character
Dynamic character

35. Static Characteristics
The instruments, which are used to measure the quantities which are slowly varying with time or mostly constant, i.e., do not vary with time, is called ‘static characteristics’.

36. STATIC CHARACTERISTICS OF AN INSTRUMENTS
Accuracy
Precision
Sensitivity
Resolution
Threshold
Drift
Error
Repeatability
Reproducibility
Dead zone
Backlash
True value
Hysteresis
Linearity
Range or Span
Bias
Tolerance
Stability

37. Resolution
This is defined as the smallest input increment change that gives some small but definite numerical change in the output.

38. Threshold
This minimum value of input below which no output can be appeared is known as threshold of the instrument.
Output
input

39. Drift
Drift or Zero drift is variation in the output of an instrument which is not caused by any change in the input; it is commonly caused by internal temperature changes and component instability.
Sensitivity drift defines the amount by which instrument’s sensitivity varies as ambient conditions change.

40. Error – The deviation of the true value from the desired value is called Error
Repeatability – It is the closeness value of same output for same input under same operating condition
Reproducibility - It is the closeness value of same output for same input under same operating condition over a period of time

41. Range
The ‘Range’ is the total range of values which an instrument is capable of measuring.

42. Hysteresis
This is the algebraic difference between the average errors at corresponding points of measurement when approached from opposite directions, i.e. increasing as opposed to decreasing values of the input.
Actual/ Input Value
Measured Value
Ideal
Hysteresis is caused by energy storage/ dissipation in the system.

43. Zero stability
The ability of the instrument to return to zero reading after the measured has returned to zero

44. Dead band
This is the range of different input values over which there is no change in output value.

45. Linearity- The ability to reproduce the input characteristics symmetrically and linearly

46. Backlash – Lost motion or free play of mechanical elements are known as backlash
True value – The errorless value of measured variable is known as true value
Bias – The Constant Error
Tolerance- Maximum Allowable error in Measurement

47. Dynamic Characteristics
The set of criteria defined for the instruments, which changes rapidly with time, is called ‘dynamic characteristics’.

48. Dynamic Characteristics
Steady state periodic
Transient
Speed of response
Measuring lag
Fidelity
Dynamic error

49. Steady state periodic – Magnitude has a definite repeating time cycle
Transient – Magnitude whose output does not have definite repeating time cycle
Speed of response- System responds to changes in the measured quantity

50. Measuring lag
Retardation type :Begins immediately after the change in measured quantity
Time delay lag : Begins after a dead time after the application of the input
Fidelity- The degree to which a measurement system indicates changes in the measured quantity without error
Dynamic error- Difference between the true value of the quantity changing with time & the value indicated by the measurement system

51. Errors in Instruments Error = True value – Measured value or
Error = Measured value - True value

52. Types of Errors Error of Measurement Instrumental error
Error of observation
Based on nature of errors
Based on control

53. Error of Measurement
Systematic error -Predictable way in accordance due to conditions change
Random error - Unpredictable manner
Parasitic error - Incorrect execution of measurement

54. Instrumental error Error of a physical measure
Error of a measuring mechanism
Error of indication of a measuring instrument
Error due to temperature
Error due to friction
Error due to inertia

55. Error of observation
Reading error
Parallax error
Interpolation error

56. Nature of Errors
Systematic error
Random error

57. Based on control Controllable errors Non - Controllable errors
Calibration errors
Environmental (Ambient /Atmospheric Condition) Errors
Stylus pressure errors
Avoidable errors
Non - Controllable errors

58. Correction
Correction is defined as a value which is added algebraically to the uncorrected result of the measurement to compensate to an assumed systematic error.
Ex : Vernier Caliper, Micrometer

59. Calibration
Calibration is the process of determining and adjusting an instruments accuracy to make sure its accuracy is with in manufacturing specifications.

60. Interchangeability
A part which can be substituted for the component manufactured to the small shape and dimensions is known a interchangeable part.
The operation of substituting the part for similar manufactured components of the shape and dimensions is known as interchangeability.