3. Overview
3
Introduction to Mechatronics
Systems
Concepts of Mechatronics Approach & Need for Mechatronics
Emerging Areas of Mechatronics
Classification of Mechatronics
Sensors and Transducers
Static and Dynamic Characteristics of Sensor
Displacement Sensors
Proximity Sensors
Temperature Sensors
Light Sensors
4. Introduction
4
Introduction - Mechatronics
The term Mechatronics was invented by a Japanese
engineer as a combination of ‘Mecha’ from Mechanisms &
‘Tronics’ from Electronics.
Definition
“The synergistic integration of mechanics &
Manufacturing engineering, electronics, computer technology &
information technology to produce products & systems”.
5. Evolution of Mechatronics
5
S.NO. YEAR INVENTIONS
1 1969 Japanese industry “yaskawa Electic corporation”
2 1971 Granted a trade mark rights for the word
3 1970-80 Most popular in europe at that time servo system is used.
4 1981-90 Information technology was introduced. (microprocessor)
5
1991-2000
Communication technology was added. (remote and
robotics)
6 1996 First journal in IEEE
7
After 2000
Application in aerospace, defence engineering, Bio-
mechanics, automotive electronics , Banking (ATM)
6. Need for Mechatronics
6
Primary objective:
To meet the industrial needs by graduates with the knowledge of integration of
Manufacturing engineering, electrical engineering & control systems.
Mechatronics engineers:
Understand the interdisplinary fundamentals and have strong skills to solve
complex problems.
Can perform research, design & implementation of intelligent products by the
integration of Manufacturing, electronics, computer & software
engaging technologies.
7. Mechatronics engineering can covers
Modeling & design
System integration
Actuators & sensors
Intelligent control
Robotics
Motion control
Vibration & noise control
Micro devices & optoelectronic systems
Automotive systems
7
A person who skilled
Design engineer
Software engineer
Project planner
Product designer
Project manager
8. Emerging Areas of Mechatronics
8
Machine vision
Servo mechanics
Sensing and control system
Expert system
Industrial goods
– medical
Home Appliances - Washing machine,
Bread machine etc
Automobile - Electrical fuel injection,
Antilock brake system
Aircraft - Flight control, Navigation
system
Automated manufacturing –
Robotics, Numerically controlled (NC)
machine tools
Medical
mechatronics
imaging system
Packaging
Mobile applications, etc
10. Advantages & Disadvantages of
Mechatronics
10
engineering
to design &
Disadvantages
Initial cost is high
Multidisciplinary
background required
implementation.
Need of skilled labors.
Complexity in identification
&
the
Advantages
Cost effective & good quality products
High degree of flexibility in design
Very good
performance characteristics
Used in wide area of applications
Greater productivity in case
of manufacturing correction of problems in
systems
11. System
11
Definition: A group of physical components connected (or) related in such a
manner to form a desire unit for performing a specific task.
All mechatronics devices consist of various systems in which some input data’s
are given to get specified output.
Eg: A motor may consider as a system which has an input as electric power and
output is the rotation of a shaft.
12. Elements of Mechatronic System
12
1) Actuators & Sensors
2) Signals & Conditioning
3) Digital Logic System
4) Software & Data Acquisition System
5) Computers & Display Devices
13. Actuators & Sensors:
Comes under Manufacturing system.
The actuator produces motion (or) causes some action.
Actuators - hydraulic, pneumatic, electrical, electroManufacturing, Manufacturing, AC
& DC motor, stepper & Servo motor, piezoelectric actuator, etc.
The sensors detect the state of the system parameters like input & output signal.
Sensors - linear sensor, rotational, acceleration, force, torque, pressure, proximity,
displacement, position, light, temperature sensor, etc.
13
14. Signals & Conditioning:
They can be classified in to two types. They are input & output signals.
The input devices receive input signal from mechatronic system
through
interfacing devices and sensors.
Then this input signal is send to the control circuit for conditioning (or)
processing.
The various input signal conditioning devices are discerete circuits, amplifiers, AD &
DA convertors.
From the system, the output signals are are send to the output devices.
The output devices are also called as display devices like DA convertors,
display decoders (DD), amplifiers, power transistors & power ampiers.
14
15. Digital Logic System:
They control the overall operation.
The various digital logic
system
15
used in mechatronics are logic circuits,
microcontroller, programmable logic controller (PLC), sequencing & time controllers,
control algorithms, etc.
Software & Data Acquisition System:
form of
Data acquisition system receives the output signal from sensors in the
voltage, frequency, resistance, etc.
These signals are then inputting in to the microprocessors.
Software’s are used to control the acquisition of the data through DAC board.
The DAC board consists of multiflexers, amplifier, register & control circuits.
Eg: data loggers, computers with plug-in-boards, etc.
16. Computers & Display Devices:
Computers are used to store large number of data’s and process further through
software.
Display devices are used to give feedback to the users.
The various display devices are used in mechatronics system are LED, CRT, LCD,
digital displays, etc.
16
18. Elements of Control System:
1) Reference variable (or) input signal
2) Response variable (or) output signal
3) Feedback – the o/p signal is returned to modify the i/p signal.
4) Error – difference between i/p & o/p signal.
5) Disturbance – any signal other than reference variable.
6) Actuating signal – difference between feedback & reference signal
7) Controlled output – the variables like temperature, position, velocity, shaft angle,
etc to guide (or) regulate the system.
8) Feedback element – used to establish feedback signal by sensing the controlled
output.
18
19. Example: Industrial Cooler System
Consider a industrial cooler in food processing unit.
Here, a required temperature should be maintained for a particular predefined
level.
Here, the input is the temperature received from the temperature sensor and the
output is to maintain a predefined temperature of the unit.
Working Function – the required temperature is set in the thermostat (or)
controller and the compressor of the cooler adjust itself by comparing the i/p &
o/p data to pump the refrigerant to produce a required temperature.
19
20. Types of Control System
20
1) Open Loop Control System
2) Closed Loop Control System
I. Open Loop (or) Feed Forward Control System
Definition:
Any physical system which does not
automatically
correct the variation in its
output. (or)
The input of the system is not controlled by the
present output.
21. Explanation:
They are also called as feed forward control system in which the output of the
system is not fed back in to the input system and not have feedback loop.
Basic Elements:
Amplifier & controller are the basic elements of open loop control system.
The amplifier receives low level input signal & amplifies it enough to drive the
controller to do desired work.
21
22. Example: Automatic Bread Toaster System
Consider an automatic bread toaster system.
Here, when the system switched ON, the heating element in the toaster heat the
bread for a particular preset time and get switched OFF and ejects the bread.
Here there is no feedback data of whether the bread is toasted properly or not.
22
23. Advantages of Open Loop Control System:
Simple & cost effective construction
Easy maintenance
Good stability
Quicker response
No calibration problem
Disadvantages of Open Loop Control System:
Less accurate
Presence of non-linearity’s cause malfunction
Slow because of manual control
Optimization in control is not possible.
System is affected by internal & external disturbances
23
24. II. Closed Loop (or) Feedback Control System
Definition:
Any physical components which automatically correct the variations by its
feedback loop.
24
25. Basic Elements:
Reference variable (or) input signal
Response variable (or) controlled variable (or) output signal
Plant – A system or process through which a particular condition is controlled.
Measuring Unit – sensors, estimators & signal conditioners.
Control Elements – need to generate the appropriate control signal applied to the
plant. Also called as controller.
Comparison Element (or) Error Junction – comparison between i/p & o/p signal.
Correction Element (or) Actuator – produce a change in the plant (or) to process the
controlled plant.
Feedback Element – need to identify the functional relationship between feedback
signal & controlled output.
25
26. Example: Room Heating Control System
In western countries, the room heating control system is used.
Here, the input signal is heat and the output signal is temperature. It can be obtained
by adjusting the thermostat.
When the desired temperature can’t be achieved, some of the heat from the output is
feedback to the thermostat.
Until the system gets desired temperature, the process continuous.
In such manner, the feedback path, input to output & feedback to input forms a ‘Closed
Loop’ control system.
26
27. Plant – Heating the room by electrical coil
Reference input – heat
Controlled Variable – Desired room temperature.
Comparison Element – Electronic Logic Circuit
Error Signal – difference between current & required temperature.
Controller – the Switch.
Correction Element – The Thermostat.
Measuring Element – The temperature sensor attached with the thermostat.
27
28. Advantages of Closed Loop Control System:
Provide much greater stability.
It gives much better repeatability
It overcomes the temperature & hysteresis effect
Faster than open loop control system
Optimization in control is possible.
Disadvantages of Closed Loop Control System:
Generally complicate in its structure.
Cost of the system is very high
28
30. Automatic Control System
30
Definition:
It is a preset closed loop control system that requires no operator action.
Most of the closed loop control systems are automatic in nature.
This assumes the process remains in the normal range for the control system.
Example:
1) Automatic Water Level Control System
2) Automatic Shaft Speed Control System
31. Example: (i) Automatic Water Level Control
System
31
1) Plant –Tank
2)Reference input – Initial setting of the float & lever
position
3)Controlled Variable – water level in a tank
4) Comparison Element – The lever
5) Error Signal – difference between actual & initial
settings of the lever position.
6)Controller – the pivoted lever
7) Correction Element – The flap opening or closing
the water supply
8)Measuring Element – The floating ball and lever.
32. Example: (ii) Automatic Shaft Speed
Control System
32
1) Plant –Rotating Shaft
2)Reference input – Setting of slider on
potentiometer
3) Controlled Variable – Speed of the rotating
shaft
4) Comparison Element – Differential amplifier
5)Error Signal – difference between input of
potentiometer and the output measured
from the tachogenerator system.
6)Controller – Differential amplifier
7) Correction Element – The motor
33. Sequential Controller
33
Definition:
It involves sequential execution of well defined operation that are performed in a
prescribed order.
In many situations, various operation of plant (or) process takes place in a
sequential order.
Example: Automatic Domestic Washing Machine
Introduction: The automatic domestic washing machine is a process of sequential
controller.
34. under four
34
Description:
The various process of automatic domestic washing machine is comes
categories.
They are Pre-Wash Cycle, Main Wash Cycle, Rinse Cycle and Spin Cycle
In older says, these processes were carried out using Cam operated switches.
35. In modern automatic domestic washing machine, the cam operating switches were
replaced by microprocessor based controllers.
Hence software is feed in to it to perform sequential operations. In addition various
sensors & drives are carried out to perform the operation.
By using time relays, the system determines the time for which cycle is to be activated.
The various sensors like speed, level, position & temperature provides the input signal to the
microprocessor.
35
36. Working Principle of Modern Automatic Domestic Washing Machine:
a) Pre Wash Cycle:
In this cycle, an electrically operated valve opens to allow the cool water in to the drum for a
period of time determined by the microprocessor.
A level sensor is used to check whether the drum is filled up to a preset level.
When the water reaches the preset level, the level sensor gives a signal to the microprocessor
to stop the water supply to the drum by switching OFF the current to the valve.
Now clothes in the drum are ready for washing in a cold wash.
After completion of cold wash, the microprocessor sends a signal to the drain pump to
drain the water from the drum.
36
37. b) Main Wash Cycle:
After the completion of pre wash cycle, the microprocessor activates the electrically
operated valve to open allow the cold water in to the drum for a period of time.
The level sensor is used to sense the water level and switch OFF the water supply to the
drum.
Now the microprocessor sends a signal to the heater to switch ON the current supply to heat
the water in the drum.
The temperature sensor gives a input signal to the microprocessor and switch OFF after a
particular preset temperature is achieved.
Now, the drum motor activates with a slow speed for a main wash for a period if time.
After completion, the microprocessor activates the drain pump to drain the water from the
drum.
37
38. c) Rinse Cycle:
When the main wash is completed, the microprocessor gives a signal to the rinse cycle. It
opens the valve to allow the cold water in to the drum and it closes when it reaches the
preset level.
The drain motor is operated to rotate the drum and drain pump is operated to drain out the
water from the drum after preset time.
This sequence is repeated for a number of times.
d) Spin Cycle:
The microprocessor switches ON the drain motor and indicates a signal to rotate the drum at a
speed then rinse cycle.
Due to centrifugal action, the water drains out from the clothes.
38
39. Sensor & Transducer
39
Sensor
Device produces a proportional output signal when exposed
phenomenon
Output - (Manufacturing, electrical, magnetic)
to a physical
Physical Phenomenon - (pressure, temperature, force, displacement)
Transducer
Device which converts an input from one form of energy in to another form.
40. Characteristics of Sensors
40
Static Characteristics:
The parameters which are more or less contact or varying very slowly with
time.
Dynamic Characteristics:
The parameters which changes with time
41. I. Static Characteristics of Sensors
1) Range
Every sensor is defined to work over a specific range which means maximum or
minimum value.
The design ranges are usually fixed.
If it exceeds, the resulting parameter will cause damage to the sensor.
Ex: for Thermocouple, the range is from -100°C to 1260°C
2) Span
Span = Maximum value of i/p – Minimum value of i/p
3)Error: The difference between measured values of output to the true value of
input
41
42. 4) Accuracy:
It is the ratio of highest deviation of the value to the ideal value.
The accuracy of the sensor is inversely proportional to the error
High accurate sensors produce low errors
42
5) Sensitivity:
43. 7) Linearity & Non-Linearity:
Linearity - Output is directly proportional to the input over its entire range (o/p VS i/p is
in straight line)
Non-Linearity - Output is not directly proportional to the input over its entire range (o/p VS
i/p forms a curve)
43
6) Hysteresis:
It is the maximum differences in output f or a given input.
It shows different output when loading & unloading.
Both loading & unloading curves do not coincide.
44. 8) Repeatability, Reproducibility& Stability:
Sensor gives same o/p for same i/p under same operating condition known as
Repeatability.
The degree of closeness among the repeated measurement of o/p for same i/p
under same operating conditions at different times known as Reproducibility.
Indicate same o/p over a period of time for a constant i/p known as Stability.
9) Resolution:
A smallest change that can be detected by a sensor.
It requires minimum value of i/p to cause an appreciable change.
44
45. 10) Drift & Zero Drift:
The variation of change in o/p for an i/p over a period of time known as Drift.
45
electronic
The result from change of temperature, electronic stabilizing &
component known as Zero Drift.
11) Impedance:
The ratio of voltage & current flow for a sensor known as impedance.
They are classified in to i/p & o/p impedance.
Input impedance – a measure of how much current drawn to power a
sensor.
Output impedance – ability of a sensor to provide current for the next stage of a
system.
46. II. Dynamic Characteristics of Sensors
1) Response Time: The time taken by a sensor to approach its true o/p when
exposed to an i/p.
2) Rise Time: Time taken by the system to reach 63.2% of its final o/p signal.
3) Setting Time: Time taken by the sensor to be with in a close range of its steady
state values.
46
47. Displacement Sensor
47
Displacement Sensor – Converts a physical change in to electrical output
Types:
1) Potentiometer
2) Strain gauge
3) Capacitive sensors
4) Linear variable differential transformer
48. Potentiometer Sensor
48
Linear Potentiometer:
It is a primary sensor which converts linear or rotary motion of a shaft in to changes in
resistance.
It is a type of resistive displacement sensor.
Linear potentiometer is the sensor that produces a resistant output proportional to the
linear displacement (or) position of the shaft.
It consist an electrically conductive linear slide member called wiper connected to a
variable wire wound resistor that changes the resistance to the linear position of the
device which is monitored.
49. As the sliding contact moves along the windings, the resistance changes in the linear
relationship with the distance from one end of the potentiometer.
To measure the typical displacement, a potentiometer is wired with a voltage divider. So
that the output voltage is proportional to the distance travelled by the wiper.
The resolution can be defined by the number of turns per unit distance and the
loading effects of the voltage divider circuit.
49
50. Rotary Potentiometer:
Rotary potentiometer is the sensor that produces a resistance output proportional to
the angular displacement (or) position of the shaft.
It consists a rotary slide member connected to a variable wire wound resistor that
changes resistance to the angular position of the device that is monitored.
The working & operating principle of rotary potentiometer is same as the linear
potentiometer.
50
51. Available in
different sizes.
Disadvantages:
Limited band width
Limited life due to wear
51
forms, ranges &
Factors to be considered:
Operating temperature
Humidity
Life cycle
Shock & vibration
Advantages:
Easy to use
Low cost
High amplitude output signal
Very high electrical efficiency
Frictional loading & Inertial loading
52. Strain Gauge Sensor
52
deforms when
It consist a structure attached with strain gauge that electrically
subjected to a displacement.
It is also a type of displacement sensor.
Strain gauge is attached to the object by a suitable adhesive.
As the member is stressed, the resulting strain deforms the strain gauge attached with a
structure.
This causes an increase in resistivity of the gauge which produces electrical
signal
proportional to the deformation.
The change of resistance can be measured by using a Wheatstone bridge circuit.
53. The strain gauge is connected with that circuit having a combination of four active
bridges forms a full bridge circuit.
The bridge is completely connected with a precision resistor where the two of these
form half bridge circuit & the single as a quarter bridge circuit.
As the stress is applied to the bonded strain gauge, a resistive changes takes place and
unbalances the wheat stone bridge.
The change in the resistance is usually less than 0.5%.
This change in resistance per unit resistance is proportional to the strain.
A wide variety of gauge size & grid shapes are available.
The metallic strain gauge consists of a very fine wire (or) metallic foil arranged in a grid
pattern.
53
55. The grid pattern maximizes the amount of wire subject to strain in the parallel
direction.
The cross sectional area of the grid is minimized to reduce the effect of shear strain &
poisson strain.
The grid is bonded in to a thin backing called carrier which is attached directly to the
test of the specimen.
The majority of the strain gauges are in bonded foil type available in various shapes &
sizes for various applications.
The principle of bonded foil type is, when a foil is subjected to stress, the resistance of
the foil changes which is small as 16mm2 & the gauge factor is 2.
The wire wound gauge is made up of copper, aluminium, nickel which has 0.0025
diameters & the length is 25mm or less than it
55
56. Advantages:
Semiconductor strain gauges has high gauge factor which allows the measurement
of
very small strain in the order of 0.01 micro strains.
Fatigue life is excess of 10 x 106 & the frequency response is up to 1012 Hz.
Hysteresis characteristics of the semi conductor strain gauge are very good.
Disadvantages:
Semiconductor strain gauge are very sensitive to change in temperature.
Linearity of the semiconductor strain gauge is very poor.
Semiconductor strain gauge is very expensive.
56
57. Linear Variable Differential Transformer
(LVDT)
57
LVDT means Linear Variable Differential Transformer (or) Transducer.
It is widely used as a variable inductive displacement sensor.
output voltage
It is a electroManufacturing device designed to produce an AC
proportional to the relative displacement of the transformer.
The physical construction of the LVDT consists of movable iron core made up of
magnetic materials & three coils forms a static transformer.
One of these coils are primary coil (or) excitation coil & the another two coils are
secondary coils (or) pick-up coils.
An AC current is passed to the primary coil & an AC output voltage is induced in
the
58. The magnetic core inside the coil winding assembly provides the magnetic flux path when
they linked with the primary & secondary coil.
When the magnetic core is in centre position (or ) null position, the output voltage is zero.
When the magnetic core is displaced from null position, number of coils are affected by the
proximity of the sliding core and thus an electromagnetic imbalance occurs.
This imbalance generates a differential AC output voltage across the secondary coil which is
linearly proportional to the direction & magnitude of the displacement.
58
60. The Rotary Variable Differential Transformer
(RVDT) is used to measure the rotational
angles & operates same as the principle of
LVDT.
Here, the RVDT uses a ferromagnetic core
material.
60
61. Advantages:
Low cost
Capable of working at any environment
High sensitive
Less power consumption
High signal to noise ratio & output impedance
Disadvantages:
Performance affected by vibration
Large displacements are required for appreciable output.
Application:
To measure displacement, deflection, position & profile of work piece.
61
62. Capacitance Sensor
62
A transducer can be used to measure the displacement by a variation in capacitance
called capacitance sensor.
Due to applied force, the elastic deflection of a membrane is detected by a variation of a
capacitance.
A capacitance sensor consists of two metal plates separated by a air gap.
The air gap between the two metallic electrodes called as dielectric constant.
The capacitance ‘C’ between the terminals is expressed by,
63. Different forms of capacitive sensors are there in the market.
The one plate capacitor is inside the probe which is sealed in an insulator and the
external target object forms the other plate of the capacitor.
The operating principle is based on the capacitance variations & the conductive
dielectric material.
The dielectric object is kept between the plates which the capacitor changes in linear
motion.
63
64. When using two plate capacitive sensors, it is in non-linear relationship between
displacements & change of capacitance.
This can be overcome by three plate capacitive sensor called push-pull displacement
sensor.
In this the upper pair forms one capacitor and the lower pair forms the other capacitor.
When the central plate moves upward, the separation of upper pair decreases and the
lower pair increases & vice versa.
The capacitance of the parallel plate capacitor is as follows,
64
65. The other type of capacitive proximity sensor is where one plate of capacitor is
connected to the central conductors of a coaxial cable while the other plate is formed by the
target object.
65
66. Eddy Current Sensor
66
It detects the proximity (or) detects the presence of a target by sensing the magnetic
field generated by the reference coil.
Eddy current sensor detect ferrous and non ferrous metals.
They can be used as a proximity sensor to detect the presence of a target (or) to
measure position / displacement of a target.
material by the
An eddy current is a local electric current induced in a conductive
magnetic field produced by the sensor coil (or) active coil.
This is sensed by a reference coil to create a output signal.
When the distance between the target & the probe changes,
correspondingly, the
impedance of the coil changes and it can be detected carefully by a arrangement of a
bridge circuit.
67. The target material is at least three times thicker than the effective depth of the eddy
current to make the transducer successful.
This is because the transducer assumes that the eddy currents are localized near the
surface of a semi-infinite solid and the actual eddy current amplitude decreases
quadratically with distance.
Advantages:
Compact in size
Low cost
High reliability
High sensitivity for small displacement
67
68. Hall Effect Sensor
68
In 1879, Edwin Hall discovered the Hall Effect sensor.
varies its output voltage in
It is a type of magnetic sensor. It is a transducer that
response with change of magnetic field.
According to his statement, when a current flowing unidirectional conductor is
introduced in a perpendicular magnetic field, a voltage could be measured at right
angles of the current path.
69. Principle: When a current carrying conductor is placed in a magnetic field, a voltage
will be generated perpendicular to both the current and the magnetic field.
69
70. The construction consists a thin sheet of semiconducting material called hall element
through which the current is passed.
The output connections are perpendicular to the current.
When there is no magnetic field, the current distribution is uniform & no potential difference is
seen across the output.
When a perpendicular magnetic field is present, a force is exerted on the current.
This force disturbs the current distribution and resulting a potential difference (voltage)
across the output.
This voltage is called as hall Voltage (VH).
70
71. This sensor can also be used to measure the fuel level in a tank.
It consists a float. As the floats gets up, the fuel becomes more. Then the gap between the magnet &
the hall sensor will be changed. It results the changing of output.
The spring allows the float to move only in vertical direction.
71
72. Temperature Sensor
72
They are widely used in industries for monitoring the system.
Temperature is defined as the average kinetic energy of the individual molecular that
comprise a system.
As the temperature increases, the molecular activity also increases & thus the average
kinetic energy is also increases.
Ex: A mercury thermometer is used to measure the fluid (or) process temperature.
They use the principle of expansion (or) contraction of liquid to measure the change in
temperature.
system use the principle of
Most of the temperature measuring (or) monitoring
expansion (or) contraction of liquid or gas or solids.
Types:
1) Bimetallic Strips
2) Thermistors
3) Resistance Temperature Detectors (RTD)
4) thermocouples
73. Bimetallic Strips
73
It is a Manufacturing thermometer.
It is widely used in industry for temperature control because of their robustness,
temperature range and simplicity.
It consists of bimetallic strips which are made of two dissimilar metals bonded together
with one end fixed & other end free.
A bimetallic strip is used to convert the temperature change in to Manufacturing
displacement.
The principle is that as the temperature increases, one strip expands more than other &
cause to bend freely.
Most bimetallic strips are high thermal expansion material at one side like stainless
steel & low thermal expansion materials like steel, copper, brass, etc
74. The metal with higher coefficient of the thermal expansion is on the outer side of the
curve when the strip is heated and cooled at the inner side.
When the temperature switch is increased, the high thermal expansion material
is
expand faster than the other side of the low thermal expansion material.
This causes the strip to bend upward making contact. So that the current can flow.
By adjusting the gap between the strip and contact, the temperature can be adjusted.
74
75. Advantages:
Power source is required
Low cost
Robust construction
Easy to use
Used up to 500oC
Disadvantages:
Less accurate
Limited applications can be used.
Not suitable for very low temperature
75
76. Resistance Temperature Detectors (RTD)
76
When the metal wire is heated, the resistance increases so that the temperature can be
measured by sing resistance of wire.
The RTD consist a pure metal (or) alloys that increases in resistance as the temperature
increases & decreases in resistance as the temperature decreases.
The RTD act as a electrical transducer which converts change in temperature to voltage
signal by the measurement of resistance.
RTD elements are made up of platinum, copper, nickel (or) nickel iron alloys. These are
the best suited for RTD application because of their linear resistance temperature
characteristics.
78. In this, the platinum wire is used as a RTD element which is surrounded by a porcelain
insulator. It prevents the system from the short circuit between the wire & the metal
sheath.
An inconel alloy (nickel-iron-chromium) is normally used to manufacture the RTD
sheath because of its corrosion resistance.
When it is placed in a liquid or gas medium, the inconel sheath quickly reaches the
temperature of the medium.
Then the change in temperature cause the platinum wire to heat or coo which is
proportional to change in resistance.
This change in resistance can be measured by a precision resistance measuring device &
calibrated for reading a proper temperature which is normally abridge circuit.
78
79. Advantages:
Suitable for measuring high temperature.
High degree of accuracy
Good stability & repeatability
No need of reference temperature junction
Disadvantages:
Size is larger than thermocouple
Power supply required
Requirement of auxiliary apparatus
Error may be occurred due to self heating & thermo electric effect.
79
80. Thermistors
80
They are the combination of thermal with resistors.
Like RTD, Thermistors are temperature sensitive resistors.
They are non-linear devices in which their resistance will decrease within increase in
temperature. But it can act faster than RTD.
The resistance can be changed more than 1000 times. As a result it can sense minute
changes in temperature which cannot achieved by RTD & thermocouple.
81. of metal
81
Thermistors are small inexpensive device that are most commonly made
oxides such as chromium, nickel, cobalt & manganese.
The metals are oxidized through chemical reaction & grinned to a fine powder.
Then it is compressed & subject to very high heat.
These oxides are semiconductors.
Based on the lead attachment, the thermistors are classified in to bead type & metalized
surface contact type.
82. In bead type, the platinum wires are sintered directly to the ceramic body where as in
metalized surface contact type, the platinum wires are not sintered directly but it is
coated with metallic contact.
One advantage of chip thermistors over bead type is that, the chips are easily trimmed by
cutting or grinding.
Depending upon the Temperature Coefficient Resistance (K), the thermistors can again
classified in to positive temperature coefficient (PTC) thermistor or posistor & negative
temperature coefficient (NTC).
If K is positive, the resistance increases with increase in temperature called PTC & if the K is
negative, the resistance decreases with increase in temperature..
PTC are most commonly used in electrical current control devices & NTC are most
commonly used in temperature sensing devices.
82
83.
83
Advantages:
High & fast output
Suitable in remote sensing areas
Can be manufactured by any shapes & sizes
Very high degree of accuracy
Good stability & repeatability
Ability to withstand Manufacturing &
electrical stresses.
Disadvantages:
Highly non-linear
Has limited measuring range
Self heating may occur
Power supply is required
84. Thermocouple
84
to the
Introduction:
A thermocouple is a device that converts thermal energy in to electrical energy.
They use a junction of dissimilar metals to generate a voltage proportional
temperature.
Thermocouples are based on Seebeck effect.
Definition: Seebeck Effect (or) Thermoelectric Effect:
In 1821, a physicist T. J. Seebeck discovered that when two conductors of
dissimilar metals of A & B are joined together to form a loop and two unequal
temperatures are interposed at the junction, then an EMF will exists between two points A & B.
this effect is known as Seebeck Effect.
86. On heating the measuring junction, voltage will be produced which greater than the
voltage produces across the reference temperature junction.
The difference between two voltages is proportional to the differences in temperature
which is measured through voltmeter.
A series of thermocouple are connected together produces a higher voltage called
thermopile.
In thermopile, all hot junctions are exposed to a higher temperature & all cold junctions
are exposed to a lower temperature.
Each thermocouple is allowed for a large voltage & increased the power output.
Thus increasing the sensitivity of the instrument readings to approach an accuracy
of
0.5%.
Some common thermocouple materials are shown below, 86
88. Laws of Thermocouple:
a)Law of Intermediate Temperature - The thermal EMF E12 produces at the junction T1 & T2
and produce the thermal EMF E23 produces at the junction T2 & T3, then the resultant EMF
generated at the junction T1 & TT3 will be E13.
b)Law of Homogeneous Material - A thermo electric current cannot sustain in a single
homogeneous material by the application of heat. It may vary in cross sections.
c)Law of Intermediate Material - If the entire junction has a uniform temperature, then
the algebraic sum of thermoelectric forces in a circuit of any number of dissimilar materials is
zero.
88
89. electrical &
89
Advantages:
Simple construction
Inexpensive
Wide temperature range
Ability to
withstand
Manufacturing stress.
Disadvantages:
Generate low voltage
Low stability
Reference source is required
Least sensitive
Applications:
Measuring the room temperature
& monitoring the presence of pilot
light in gas fed appliances are ovens & water
heaters.
S, R & K type of thermocouples are used in
steel & iron industry to monitor the
temperature.
Used to measure intensity of incident
radiation, IR lights.
Used to testing the prototype electrical &
Manufacturing apparatus
