This ppt includes the first chapter of MEM, I scheme, SY Mechanical Engineering, MSBTE, Mumbai.

1. INTRODUCTION TO MEASUREMENT
By :
Prof. Gadkar Sagar P.
Assistant Professor,
Mechanical Department,
G.H.Raisoni College of
Engineering,

2. Measurement
• The measurement of a given quantity is essentially an actor
result of comparison between a quantity, whose magnitude is
unknown with a similar quantity whose magnitude is known,
the latter being called standard.

3. • Essential elements of scientific instruments
• A Detector
• An intermediate transfer devices
• An indicator, recorder or a storage device

4. Mechanical Instruments
• Very reliable for static and stable condition
• Unable to respond rapidly to measurements
of dynamic and transient condition
• Due to rigid, heavy and bulky parts have large
mass hence cannot faithfully follow the rapid
change
• Are potential source of noise pollution

5. Electrical Instruments
• Electrical instrument are more rapid than
mechanical type
• An electrical system normally depends upon a
mechanical meter movement as indicating
device

6. Electronic Instruments
• Today’s requirement of measuring instrument
is very fast response
• Electronic instrument uses semiconductor
devices
• Since in electronic devices, the only
movement involved is that of electrons the
response time is very small

7. Functions of Instruments
and Measurement
Systems
• Indicating Function:-
• Recording Function:-
• Controlling Function:-

8. Types of
Instruments
• Mode of measurement
• Primary Instrument
• Secondary Instrument
• Tertiary Instrument
• Nature of Contact
• Contact type
• Non Contact type

9. Types of Instruments
continued
• Signal Being Processed
• Analog Measuring Instrument
• Digital Measuring Instrument
• Condition of Pointer
• Null Type
• Deflection type
• Power Source Required
• Self sufficient Instrument (Active )
• Power operated instrument (Passive)

10. Functional Elements of an
Instrumentation system
• Primary Sensing Element
• Variable Conversion Element
• Variable Manipulation Element
• Data Transmission Element
• Data Presentation Element

11. Functional Elements of an
Instrumentation systemUnknow
n
Primary
Sensing
Element
Variable
Conversion
Element
Variable
Manipulation
Element
Data
Transmission
Element
Data
Presentation
Element
Outpu
t

12. CHARACTERISTICS OF
MEASUREMENT SYSTEM

13. CHARACTERISTICS OF MEASUREMENT
SYSTEMS
 A knowledge of the performance characteristics of an instrument is
essential for selecting the most suitable instrument for specific measuring
jobs
 The performance characteristics may be broadly divided into two groups,
namely
Static characteristics
Dynamic characteristics

14. STATIC and DYNAMICS CHARACTERISTICS
OF MEASUREMENT SYSTEMS

15. STATIC CHARACTERISTICS OF INSTRUMENT
 Static characteristics of an instruments are concerned only with
steady state readings
 Accuracy and Precision
 Range or Span
 Linearity & Sensitivity
 Repeatability
 Reproducibility
 Hysteresis
 Threshold
 Resolution
 Dead space

16. ACCURACY
 The accuracy of an instrument is a measure of how close the output reading
of the instrument is to the true value
 In practice, it is more usual to quote the inaccuracy or measurement
uncertainty value rather than the accuracy value of an instrument
 Inaccuracy or measurement uncertainty is often quoted as a percentage of
the full-scale reading of an instrument
 Accuracy can be improved by calibration

17. PRECISION
 Precision is a term that describes an instrument’s degree of freedom from
errors . If a large number of readings are taken of the same quantity by a
high-precision instrument, then the spread of readings will be very small
 Accuracy can be improved by calibration but not precision
 If you weigh a given substance five times, and get 3.2 kg each time, then
your measurement is very precise. Precision is independent of accuracy.
You can be very precise but inaccurate

18. ACCURACY & PRECISION

19. The figure shows the results of tests on three
industrial robots that were programmed to place
components at a particular point on a table.
The target point was at the center of the
concentric circles shown, and the black dots
represent the points where each robot actually
deposited components at each attempt. Both the
accuracy and precision of Robot 1 is shown to be
low in this trial.
Robot 2 consistently puts the component down at
approximately the same place but this is the
wrong point. Therefore, it has high precision but
low accuracy.
Finally, Robot 3 has both high precision and high
accuracy, because it consistently places the
component at the correct target position
ACCURACY vs. PRECISION

20. RANGE OR SPAN AND FULL SCALE
 The range or span of an instrument defines the minimum and maximum
values of a quantity that the instrument is designed to measure
Example: A particular micrometer is
designed to measure dimensions between 50
and 75 mm. What is its measurement range?
Ans: The measurement range is simply the
difference between the maximum and
minimum measurements. (25 mm)

21. REPEATABILITY & REPRODUCIBILITY
 Repeatability and Reproducibility (R & R) Studies evaluate the precision of a
measurement system. It is important that the instrument properly calibrated before
starting R & R study
 Repeatability describes the closeness of output readings when the same input is applied
repetitively over a short period of time, with the same measurement conditions, same
instrument and observer, same location, and same conditions of use maintained
throughout
 Reproducibility describes the closeness of output readings for the same input when there
are changes in the method of measurement, observer, measuring instrument, location,
conditions of use, and time of measurement

22. THRESHOLD
 If the input to an instrument is gradually increased from zero, the input will
have to reach a certain minimum level before the change in the instrument’s
output reading. This minimum level of input is known as the threshold of
the instrument. Example: Eddy current Speedometer used in automobiles
typically have a threshold of about 15km/h

23. RESOLUTION
 Using a car speedometer as an example again, this has subdivisions of
typically 10 miles/h. This means that when the needle is between the scale
markings, we cannot estimate speed more accurately than to the nearest 5
miles/h. This value of 5 miles/h thus represents the resolution of the
instrument.

24. SENSITIVITY
 Sensitivity is the smallest amount of difference in quantity that will change
an instrument's reading
 Sensitivity of a spring balance can be expressed as 25 mm/kg (say), indicating
additional load of 1 kg will cause additional displacement of the spring by 25mm
 Sensitivity of an instrument may also vary with temperature or other external or
Environmental factors. This is known as sensitivity drift
 Suppose the sensitivity of the spring balance mentioned above is 25 mm/kg at 20
oC and 27 mm/kg at 30oC. Then the sensitivity drift/oC is 0.2 (mm/kg)/oC
 In order to avoid such sensitivity drift, sophisticated instruments are either kept at
controlled temperature, or suitable in-built temperature compensation schemes are
provided inside the instrument

25. SENSITIVITY
 The sensitivity of measurement is a measure of the change in instrument output that
occurs when the quantity being measured changes by a given amount Thus, sensitivity
is the ratio:
 For example, a pressure of 2 bar produces a deflection of 10 degrees in a pressure
gauge, the sensitivity of the instrument is 5 degrees/bar (assuming that the deflection
is zero with zero pressure applied)

26. LINEARITY
 Linearity is defined as the ability of an
instrument to reproduce its input linearly
 Linearity is simply a measure of the
maximum deviation of the calibration points
from the ideal straight line
 Linearity is defined as,
Maximum deviation of output from idealized
straight line ∕ Actual readings
 The X’s marked on Figure show a plot of the
typical output readings of an instrument when
a sequence of input quantities are applied to it
 The nonlinearity is then defined as the
maximum deviation of any of the output
readings marked X from this straight line.
Nonlinearity is usually expressed as a
percentage of full-scale reading

27. HYSTERESIS
 Figure shows illustrates the output characteristic of
an instrument that exhibits hysteresis. If the input
measured quantity to the instrument is steadily
increased from a negative value, the output reading
varies in the manner shown in curve (A)
 If the input variable is then steadily decreased, the
output varies in the manner shown in curve (B).
The non coincidence between these loading and
unloading curves is known as hysteresis
 Two quantities are defined, maximum input
hysteresis and maximum output hysteresis, as
shown Figure. Hysteresis is most commonly found
in instruments that contain springs, such as the
passive pressure gauge

28. DEAD SPACE/DEAD ZONE
 Dead space is defined as the range of different input
values over which there is no change in output
value.
 Some instruments that do not suffer from any
significant hysteresis can still exhibit a dead space
in their output characteristics however
 Backlash in gears is a typical cause of dead space,
and results in the sort of instrument output
characteristic shown in Figure.

29. 2.Dynamic Characteristics
Instruments rarely respond to the instantaneous
changes in the measured variables.Their response is
slow or sluggish due to mass, thermal capacitance,
electrical capacitance, inductance etc. sometimes,
even the instrument has to wait for some time till, the
response occurs.
These type of instruments are normally used for the
measurement of quantities that fluctuate with time.
The behaviour of such a system, where as the input
varies from instant to instant, the output also varies
from instant to instant is called as dynamic
response of the system.
Hence, the dynamic behaviour of the system is also
important as the static behaviour.

30. The dynamic inputs are of two types:
1. Transient
2. Steady state periodic.
 Transient response is defined as that part of
the response which goes to zero as the time
becomes large.
 The steady state response is the response
that has a definite periodic cycle.

31. The variations in the input, that are used
practically to achieve dynamic behaviour are:
I. Step input:-The input is subjected to a finite
and instantaneous change. E.g.: closing of
switch.
II. Ramp input:- The input linearly changes with
respect to time.
III. Parabolic
square of
input:- The input varies to the
time. This represents constant
input:- The input
acceleration.
IV. Sinusoidal
accordance with a sinusoidal
changes in
function of
constant amplitude.

32. The dynamic characteristics of a measurement
system are:
1) Speed of response
2) Fidelity
3) Lag
4) Dynamic error

33. 1) Speed of Response
It is defined as the rapidity with which an
instrument, responds to the changes in the
quantity.
It shows measured how active and fast the system
is.
Speed measuring instruments:-

34. 2) Fidelity
It is defined as the degree to which a
measurement system is capable of faithfully
reproducing the changes in input, without any
dynamic error.

35. 3)Lag
Every system requires its own time to respond to
the changes in input. This time is called as lag.
It is defined as the retardation or delay, in the
response of a system to the changes in the input.
The lags are of two types:
1. Retardation lag:
As soon as there is a changes in the
measured quantity, the measurement system
begins to respond.
2. Time delay:
The response of the measurement system
starts after a dead time, once the input is
applied.They cause dynamic error.

36. 4)Dynamic error
It is the difference between the true value of
the quantity that is to be measured, changing
with time and the measured value, if no static
error is assumed.

37. MEASUREMENT OF ERROR

38. No Measurement is Accurate!
 Errors occur because of:
1. Parallax error (incorrectly sighting the
measurement).
2. Calibration error (if the scale is not accurately
drawn).
3. Zero error (if the device doesn’t have a zero
or isn’t correctly set to zero).
4. Damage (if the device is damaged or faulty).
5. Limit of reading of the measurement device (the
measurement can only be as accurate as the
smallest unit of measurement of the device).

39. Definitions
1. Limit of Reading: is the smallest unit of
measurement on the measuring instrument.
2. The Greatest Possible Error (also called the
absolute error): is equal to half the limit of
reading.
3. The Upper and Lower Limits: are the smallest
and largest value between which a measurement
can lie.

40. Types of
Errors
Basically Three types of errors are
studied:-
1. Gross Errors
2. Systematic Errors
3. Random Errors

41. Gross
Errors
Gross Errors mainly covers the human mistakes in
reading instruments and recording and calculating
measurement results.
Example:- Due to oversight, The read of Temperature
as 31.5 ̊ while the actual reading may be 21.5 .

42. Gross Errors may be of any amount and then
their mathematical analysis is impossible. Then
these are avoided by adopting two means:-
1.Great care is must in reading and recording
the data.
2.Two , Three or even more reading should be
taken for the quantity under measurement.

43. Systematic Errors
Systematic Errors classified into three categories :-
1. Instrumental Errors
2. Environmental Errors
3. Observational Errors

44. Instrumental Errors
These errors arises due to three main reasons.
1. Due to inherent shortcoming in the instrument.
Example:- If the spring used in permanent magnet
instrument has become weak then instrument will
always read high. Errors may caused because of
friction , hysteresis , or even gear backlash.
2. Due to misuse of the instruments.
3. Due to Loading effects of instruments.

45. Environmental Errors
These errors are due to conditions external to
the measuring Device including conditions in
the are surrounding the instrument.
These may be effects of Temperature, Pressure,
Humidity, Dust, Vibrations or of external
magnetic or electrostatic fields.

46. Observational Errors
There are many sources of observational
errors:-
-- Parallax, i.e. Apparent displacement when the
line of vision is not normal to the scale.
-- Inaccurate estimate of average reading.
-- Wrong scale reading and wrong recording the
data.
-- Incorrect conversion of units
between consecutive reading.

47. Here in Graph, Full Line shows the systematic Error in non
Linear Instrument.
While Broken Line shows response of an ideal instrument
without Error.

48. Random Errors
The quantity being measured is affected by many
happenings in the universe. We are aware for
some of
measurement,
the factors influencing the
but about the rest we are
unaware. The errors caused by happening or
disturbances about which we are unaware are
Random Errors. Its also known as residual
Errors.

49. Classification of Transducers

50. Transducers
• A Transducer is a device which converts one
form of energy into another form.
• Alternatively, a Transducer is defined as a device
which provides usable output response to a
specific input measured which may be a
physical quantity.
• A Transducer can also be defined as a device
when actuated by energy in one system supplies
energy in the same form or in another form to a
second system.

51. Classification of Transducers
• Transducers may be classified according to their
application, method of energy conversion, nature of
the output signal, and so on.
•
Transducers
On The Basis of
principle Used
Active/Passive Primary/Secondary Analog/Digital
Transducers/
Inverse
Transducers
Capacitive
Inductive
Resistive

52. Active and Passive
Transducers
• Active transducers :
• These transducers do not need any external source of power for
their operation. Therefore they are also called as self generating
type transducers.
I. The active transducer are self generating devices which operate
under the energy conversion principle.
II. As the output of active transducers we get an equivalent
electrical output signal e.g. temperature or strain to electric
potential, without any external source of energy being used

53. Classification of Active
Transducers

54. Example of active transducers
• Piezoelectric Transducer- When an external
force is applied on to a quartz crystal, there will be a
change in the voltage generated across the surface.
This change is measured by its corresponding value
of sound or vibration.

55. Passive Transducers
• These transducers need external source of power for
their operation. So they are not self generating type
transducers.
• A DC power supply or an audio frequency generator is
used as an external power source.
• These transducers produce the output signal in the
form of variation in electrical parameter like resistance,
capacitance or inductance.
• Examples – Thermistor, Potentiometer type transducer

56. Primary and Secondary
Transducers
• Some transducers contain the mechanical as well as
electrical device. The mechanical device converts the
physical quantity to be measured into a mechanical
signal. Such mechanical device are called as the
primary transducers, because they deal with the
physical quantity to be measured.
• The electrical device then convert this mechanical
signal into a corresponding electrical signal. Such
electrical device are known as secondary transducers.

57. Example of Primary and secondary
transducer
Primary transducer
Displacement
voltage
Secondary transducer

58. According to Transduction
principle used

59. Capacitive Transduction:
• Here, the measurand is converted into a change in
capacitance.
• A change in capacitance occurs either by changing
the distance between the two plates or by changing
the dielectric.
d
Area=A

60. Electromagnetic transduction:
• In electromagnetic transduction, the measurand is
converted to voltage induced in conductor by change
in the magnetic flux, in absence of excitation.
• The electromagnetic transducer are self generating
active transducers
• The motion between a piece of magnet and an
electromagnet is responsible for the change in flux

61. Inductance Transduction:
• In inductive transduction, the measurand is converted
into a change in the self inductance of a single coil. It
is achieved by displacing the core of the coil that is
attached to a mechanical sensing element
Piezoelectric Transduction:
• In piezoelectric induction the measurand is converted
into a change in electrostatic charge q or voltage V
generated by crystals when it is mechanically
stressed.

62. Photovoltaic Transduction:
• In photovoltaic transduction the measurand is
converted to voltage generated when the
junction between dissimilar material is
illuminated.

63. Photoconductive Transduction:
• In photoconductive transduction the
measurand is converted to change in resistance
of semiconductor material by the change in
light incident on the material.

64. Analog and Digital Transducers
Analog transducers:
• These transducers convert the input quantity into an
analog output which is a continuous function of time.
• Thus a strain gauge, an L.V.D.T., a thermocouple or a
thermistor may be called as Analog Transducers as they
give an output which is a continuous function of time.
Digital Transducers:
• These transducers convert the input quantity into an
electrical output which is in the form of pulses and its
output is represented by 0 and 1.

65. Transducer and Inverse
Transducer
Transducer:
• Transducers convert non electrical quantity to
electrical quantity.
Inverse Transducer:
• Inverse transducers convert electrical quantity
to a non electrical quantity. A piezoelectric
crystal acts as an inverse transducer because
when a voltage is applied across its surfaces, it
changes its dimensions causing a mechanical
displacement.

66. THANK YOU