2. MEASUREMENT
• Developments in science and technology
• Comparing unknown quantity with a predefined standard
• Quantifying an event or thing
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3. Instrumentation
• Instrumentation deals with measurement and
control of various nonelectrical parameters.
• Electrical parameters: V,I,R,C,L,Z,etc
• Non-electrical parameters:
• Temperature, Pressure, Flow, Level, etc
• Measure, monitor, Analyse, control and
Record various parameters.
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9. Purpose of measurement
• To understand an event or operation
• To monitor an event or operation
• To control an event or operation
• To collect data for future analysis
• To validate an engineering design
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10. Functional blocks of a
Measurement system
Input
Sensing
Element Signal Conditioner Data presenting
Device
Output
Power supply
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11. • Input: Physical quantity to be measured
• Sensing device: Sensor/Transducer
• Signal conditioner: output of transducer to the
convenient form for further processing
– Linearisation, demodulation, filtering,
amplification, ADC
• Data presenting device: present the measured
quantity to observer
– Pointer, Recorder, LCD, LED, Printer, Monitor
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15. Primary sensing element
• The primary sensing element is also known as
sensor.
• Basically transducers are used as a primary
sensing element.
• Here, the physical quantity (such as
temperature, pressure etc.) are sensed and
then converted into analog signal.
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16. • Variable conversion element
– It converts the output of primary sensing element
into suitable form without changing information.
Basically these are secondary transducers.
• Variable manipulation element
– The output of transducer may be electrical signal
i.e. voltage, current or other electrical parameter.
Here, manipulation means change in numerical
value of signal.
– This element is used to convert the signal into
suitable range.
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17. • Data transmission element
– Sometimes it is not possible to give direct read out of the
quality at a particular place (Example – Measurement of
temperature in the furnace).
– In such a case, the data should transfer from one place to
another place through channel which is known as data
transmission element.
– Typically transmission path are pneumatic pipe, electrical
cable and radio links.
– When radio link is used, the electronic instrumentation
system is called as telemetry system.
• Data presentation or controlling element
– Finally the output is recorded or given to the controller to
perform action.
– It performs different functions like indicating, recording or
controlling.
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21. Sensors Vs Transducers
• Sensor is a device which responds to physical
stimulus
• Transducer is a device which converts one
form of energy to another.
• Non-electrical quantity is converted to
electrical quantity.
– Sensing element: sensor/detector
– Transduction element
– Sensor is a part of transducer
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31. Sensor -Applications
• As per the definition of a sensor, it is a physical
device that is useful for measuring the changes in
the surroundings after measuring their physical
quantities (light, heat, sound, etc.) and
transforming them into signals (current, voltage,
etc.) that can be easily read by users.
• Motion sensors are applied in home security
systems as well as automation door systems.
• Photosensor sense changes in infrared/ultraviolet
light.
• Accelerometer sensors are utilized in the mobile
to detect screen rotations.
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32. A key difference between transducer and
sensor
• The sensor senses the physical changes in the form of
precise quantities to users. On the other hand, a transducer
is used for transforming a specific kind of energy into a
different format.
• The sensor does not have any other component for
sensing/ processing purposes, while a sensor and signal
conditioning unit are used for making a transducer work.
• The sensor primarily functions to sense physical changes in
the environment; on the other hand, a transducer is used
for converting physical quantities into electrical signals.
• The examples of sensors are a barometer, gyroscope,
accelerometer, etc. The thermocouple, thermistor,
antennas, etc. are examples of transducers.
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33. UNITS
• Standard measure of each kind of physical quantity.
• The result of a measurement of physical quantity must be
defined both in kind and magnitude.
TYPES OF UNITS
Fundamental units Derived units
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34. Fundamental units and Derived units
• Fundamental units: Units which are fundamental to most
other physical quantities are called fundamental unit.
• Eg: Length, mass, time, electric current, temperature and
luminous intensity
• Derived units: All other units which can be expressed in terms
of fundamental units are called derived units.
Eg: Velocity= Distance
Time
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38. Systems of units
• FPS system (Foot, Pound, Second)
• CGS system ( Centimeter, Gram, Second)
• MKS system (Meter, Kilogram, Second)
• Rationalised MKSA system (Meter, Kilogram,
Second, Ampere)
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39. Standards of Measurement
• The physical representation of a unit of
measurement is called standard.
Classification Of Standards:
• Standards are classified by their functions as-
1) International standards
2) Primary standards
3) Secondary standards
4) Working standards
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40. International Standards
• International standards are standards accepted
internationally.
• It is maintained by International Bureau of weights and
measures near Paris.
• They are not available for common users for the
purpose of calibration or comparison.
• It represents the units of measurement which are
closest to the possible accuracy attainable with
present day technological and scientific methods.
• It is checked and evaluated regularly against absolute
measurements in terms of fundamental units.
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41. Primary Standards
• It is maintained by National Standards laboratory
in different parts of the world.
• In India, National physical laboratory at New
Delhi is responsible for maintaining primary
standards.
• Not available for use outside the national
laboratories.
• The main function of primary standards is the
verification and calibration of secondary
standard.
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42. Secondary Standards:
• Secondary standards are Basic reference standards available in
different laboratories. It is used in Industrial measurement
laboratories.
• It is easily accessible to all measurement engineers.
Working Standards:
• It is used to check and calibrate general laboratory instruments for
their accuracy and performance.
Fundamental Standards:
• The four fundamental quantities of the International Measuring
system for which independent standards have been defined are :
mass, length , time and temperature.
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43. • International standard for mass is standard kilogram which is mass
of platinum-iridium cylinder preserved at International Bureau of
Weights and Measures in France.
• International standard for length is standard meter which is
represented by the distance between two lines engraved on a
platinum-iridium bar preserved again in France.
• Fundamental unit of time, the second has been defined as the
interval of time corresponding to 9,192,631,770 cycles of the
atomic resonant frequency of cesium 133.
• Temperature – kelvin –thermodynamic temperature of triple point
of water at exactly 273.16degK.
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44. • Some Other Common Standards Are:
• Electrical Standards
• Standards for luminous intensity
• Standards for pressure
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45. Sensors- Types
• Temperature Sensor.
• Proximity Sensor.
• Accelerometer.
• IR Sensor (Infrared Sensor)
• Pressure Sensor.
• Light Sensor.
• Ultrasonic Sensor.
• Smoke, Gas and Alcohol Sensor.
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49. Classification of transducers
• ISA- International Society for Measurement and Control- USA
defines transducer as a sensing device that converts physical
phenomenon into electrical, pneumatic or hydraulic output
signal.
• A transducer is defined as a device which, when actuated by
one form of energy is capable of converting to another form
of energy.
• Hence, transducers can be defined as devices which when
convert one form of signal into another form preferably
electrical form.
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50. Classification of transducers
• Transducers classified in three different ways.
1) Based on the physical effect employed
2) Based on the physical quantity they convert
3) Based on source of energy for their output
1) Classification based on physical effect employed:
• The physical quantity applied as measurand (quantity to be
measured) to the transducer causes some physical changes in
its element.
By this physical effect the transducer converts the physical
quantity in to electrical quantity.
Example: change in temperature to be measured causes
variation of-resistance (physical change) in a copper wire
(element) and this effect could, be used to convert
temperature in to an electrical output.
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51. • The physical effects commonly employed are
– Variation of resistance
– Variation of inductance
– Variation of capacitance
– Piezo electric effect
– Magnetostrictive effect
– Elastic effect
– Hall effect
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53. Variation of resistance
• Resistance thermometer: – thermo resistive effect – change
in electrical resistivity of a metal due to change in
temperature coefficient of resistivity.
• Carbon microphone: – change in contact resistance due to
applied pressure.
• Photo conductive cell: – based upon photoconductive effect
which is the change in electrical conductivity due to incident
light.
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55. Variation of capacitance
Eg: Capacitor microphone – converts sound pressure into an
electrical signal
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56. • Piezoelectric effect:
– Whenever a piezoelectric crystal like quatrz or Rochelle
salt is subjected to mechanical stress, an electric charge is
generated. This is known as piezoelectric effect. The
transducer based on this effect is piezoelectric transducer.
• Magnetostrictive effect:
The permeability of magnetic material changes when it is
subjected to a mechanical stress. This is called villari effect.
• Elastic effect:
When an elastic member is subjected to mechanical stress
it is deformed. The transducer based on this effect is called
elastic transducer.
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57. • Hall effect:
When a magnetic field is
applied to a current
carrying conductor at
right angles to the
direction of current, a
transverse electric
potential gradient is
developed in the
conductor.
This effect is called as
Hall effect and the
transducer based on this
effect is called as Hall
effect transducer.
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58. 2. Classification based on physical quantity
measured
• Temperature transducers - Transducers used to measure
temperature
• Pressure transducers - To measure pressure
• Flow transducers - To measure flow
• Liquid level transducers – To measure liquid level
• Force/Torque transducers - To measure force & Torque
• Velocity/Speed transducers - To measure velocity & speed
• Humidity transducers - To measure humidity
• Acceleration/vibration transducers - To measure
acceleration & vibration
• Displacement transducers – To measure displacement
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59. 3. Classification based on source of energy
• Transducers may be, classified based on source of energy into
two types.
• Active transducer
• Passive transducer
1. 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.
• The active transducer are self generating devices which operate under the
energy conversion principle.
• As the output of active transducers we get an equivalent electrical output
signal
• They produce an electrical signal proportional to the input (physical
quantity).
• For example: Thermocouple, Piezoelectric transducer, Photovoltaic cell
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65. Passive Transducers
• These transducers need external source of power for their
operation.
• These transducers produce the output signal in the form of
variation in resistance, capacitance, inductance or some other
electrical parameter in response to the quantity to be
measured.
• Example: Resistive, Inductive, Capacitive
transducers
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75. Characteristics of transducer
• Instrumentation system Design – selection of transducers
• For the proper selection of transducer, knowledge of the
performance characteristics of transducer is essential.
• The performance characteristics can be classified into two
namely
(i) Static characteristics
(ii) Dynamic characteristics
• Static characteristics are a set of performance criteria that
give a meaningful description of the quality of measurement
while the measured quantities are either constant or vary
slowly with time.
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76. Dynamic characteristics
• Dynamic characteristics describe the quality of
measurement when the measured quantities
vary rapidly with time.
• Here the dynamic relations between the
instrument input and output must be
examined, generally by the use of differential
equations.
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77. Static characteristics - Review
• The most important static characteristics of a
transducer are
1. Static sensitivity
2. Linearity
3. Precision / Accuracy
4. Threshold
5. ResoIution
6. Hysteresis
7. Range and span
8. Input impedance and loading effect.
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78. Static calibration
• All these static characteristics are obtained by one form
or another of the process of static calibration.
• Transducer responds to number of inputs out of which
one may be the desired quantity.
• In general, static calibration refers to a situation in
which all inputs except the desired one are kept at
some constant values.
• The desired input is varied over some range in steps
and the output values are noted.
• The input - output relationship thus developed is called
the static calibration.
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80. Accuracy and Precision
Accuracy:
• The accuracy of an instrument is a measure of how close the
output reading of the instrument is to the true value.
• Inaccuracy or measurement uncertainty is often quoted as a
percentage of the full-scale reading of an instrument
• Accuracy can be improved by calibration.
Precision:
• Precision is the degree of closeness with which a given value
may be repeatedly measured.
• It is a measure of the reproducibility of the measurements.
• Accuracy is closeness to true value but Precision is
closeness among the readings
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86. Range and span
• Generally a transducer is recommended to be used
between a high and a low values of input.
• The range of the transducer is specified as from the
low value of input to the high value of input.
• The span of the transducer is specified as the
difference between the high and the low limits of
recommended input values.
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87. Example
• For example, if a temperature transducer is
recommended to be used between 200°C and
800°C, its range is specified as
_______whereas its span is_______
• When an ammeter is specified to be used
between 0 and 100 mA, its range is 0 to
100 mA and its span is 100 mA.
(i.e. 100 mA - 0 mA = 100 mA).
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88. Threshold
• When the input to a transducer is increased gradually from
zero, there is a minimum value below which no output can
be detected.
• This minimum value of the input is defined as the threshold
of the transducers.
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90. Resolution
• When the input to a transducer is
slowly increased from some
arbitrary (non-zero) value, the
change in output is not detected at
all until a certain input increment is
exceeded.
• This increment is called resolution or
discrimination of the instrument.
• Resolution defines the smallest
measurable input change while the
threshold defines the smallest
measurable input at the beginning.
• The resolution of digital instruments
is decided by the number of digits
used for display.
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91. Example
• For example, the resolution of a four-digit
voltmeter with a range of 999.9 volts is 0.1
volt.
• Whereas for a five-digit voltmeter of the same
range, the resolution would be 0.01 volt.
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92. Hysteresis
• Hysteresis is a phenomenon which depicts different output
effects when loading and unloading whether it is a mechanical
system or an electrical system.
• Hysteresis is non-coincidence of loading and unloading
curves.
• When the input to a transducer which is initially at rest is
increased from zero to full-scale and then decreased back to
zero, there may be two output values for the same input.
• This mismatching of the input-output curves is mainly due to
internal friction and change in damping of the spring
elements in the transducer.
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93. Hysterisis Effect
• Hysteresis effects can be
minimised by taking
readings corresponding
to ascending and
descending values of
the input and then
taking their arithmetic
average.
• Elastic members spring,
diaphragm, bellows
exhibit considerable
amount of hysterisis
effect
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94. Linearity
• Linearity is a measure of the maximum
deviation of the plotted transducer response
from a specified straight line.
• The calibration curve of a transducer may not
be linear in many cases.
• • If it is so, the transducer may still be highly
accurate.
• • However, linear behaviour is most desirable
in many applications.
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96. • A wheatstone bridge requires a change of
7ohm in the bridge produces a change in
deflection of 3mm of galvanometer.
Determine the sensitivity.
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97. • A pressure measurement instrument is
calibrated between 10 bar and 250 bar. The
scale span of the instrument is ________
• Range of instrument is ________
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