ME 6702-Mechatronics

Unit-1- Introduction to Mechatronics

ME6702 - Mechtronics
Unit I Notes
What is “Mechatronics”?
Mechatronics is a concept of Japanese origin (1970’s) and can be defined as the application
of electronics and computer technology to control the motions of mechanical systems (figure 1.1.1).

It is a multidisciplinary approach to product and manufacturing system design (Figure 1.1.2).

It involves application of electrical, mechanical, control and computer engineering to develop
products, processes and systems with greater flexibility, ease in redesign and ability of
reprogramming. It concurrently includes all these disciplines.

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Mechatronics can also be termed as replacement of mechanics with electronics or enhance

mechanics with electronics. For example, in modern automobiles, mechanical fuel injection systems
are now replaced with electronic fuel injection systems. This replacement made the automobiles
more efficient and less pollutant. With the help of microelectronics and sensor technology,
Mechatronics systems are providing high levels of precision and reliability. It is now possible to
move (in x – y plane) the work table of a modern production machine tool in a step of 0.0001 mm.
By employment of reprogrammable microcontrollers/microcomputers, it is now easy to add new
functions and capabilities to a product or a system. Today’s domestic washing machines are
“intelligent” and four-wheel passenger automobiles are equipped with safety installations such as
air-bags, parking (proximity) sensors, antitheft electronic keys etc.

Basic Elements of Mechatronics system

The basic elements of Mechatronics system are

1. Input signal
2. Controller
3. Mechanical system
4. Sensor
5. Microcontroller
6. Output

Computer elements refer to hardware/software utilized to perform computer-aided

dynamic system analysis, optimization, design, and simulation; virtual instrumentation; rapid
control prototyping; hardware-in-the-loop simulation; and PC-based data acquisition and
control

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Control interface/computing hardware elements refer to analog-to-digital (ADC)

converter, digital-to-analog (DAC) converter, digital input/output (I/O), counters, timers,
microprocessor, microcontroller, data acquisition and control (DAC) board, and digital signal
processing (DSP) board. The control interface hardware allows analog/digital interfacing,
i.e., communication of sensor signal to the control computer and communication of control
signal from the control computer to the actuator. The control computing hardware
implements a control algorithm, which uses sensor measurements, to compute control actions
to be applied by the actuator.

Electrical elements refer to electrical components (e.g., resistor (R), capacitor (C),
inductor (L), transformer, etc.), circuits, and analog signals. Electronic elements refer to
analog/digital electronics, transistors, thyristors, opto-isolators, operational amplifiers, power
electronics, and signal conditioning. The electrical/electronic elements are used to interface
electro-mechanical sensors and actuators to the control interface hardware elements.

Electromechanical elements refer to sensors and actuators. A variety of physical

variables can be measured using sensors, e.g., light using photo-resistor, level and
displacement using potentiometer, direction/tilt using magnetic sensor, sound using
microphone, stress and pressure using strain gauge; touch using micro-switch; temperature
using thermistor and humidity using conductivity sensor. Actuators such as light emitting
diode (LED), DC servomotor, stepper motor, relay, solenoid, speaker, shape memory alloy,
electromagnet, and pump apply commanded action on the physical process. In recent years,
IC-based sensing and actuation solutions have also become ubiquitous (e.g., digital-compass,
-potentiometer, etc.).

Mechanical elements refer to mechanical structure, mechanism, thermo-fluid, and

hydraulic aspects of a mechatronics system. The mechanical element may include
static/dynamic characteristics and it interacts with its environment purposefully. The
mechanical elements of mechatronics systems require physical power to produce motion,
force, heat, etc.

Importance of Mechatronics in automation

Today’s customers are demanding more variety and higher levels of flexibility in the
products. Due to these demands and competition in the market, manufacturers are thriving to launch
new/modified products to survive. It is reducing the product life as well as lead-time to manufacture
a product. It is therefore essential to automate the manufacturing and assembly operations of a
product. There are various activities involved in the product manufacturing process. These are
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shown in figure 1.1.3. These activities can be classified into two groups viz. design and
manufacturing activities

Mechatronics concurrently employs the disciplines of mechanical, electrical, control and

computer engineering at the stage of design itself. Mechanical discipline is employed in terms of
various machines and mechanisms, where as electrical engineering as various electric prime movers
viz. AC/DC, servo motors and other systems is used. Control engineering helps in the development
of various electronics based control systems to enhance or replace the mechanics of the mechanical
systems. Computers are widely used to write various softwares to control the control systems;
product design and development activities; materials and manufacturing resource planning, record
keeping, market survey, and other sales related activities.

Using computer aided design (CAD) / computer aided analysis (CAE) tools, three
dimensional models of products can easily be developed. These models can then be analyzed and
can be simulated to study their performances using numerical tools. These numerical tools are being
continuously updated or enriched with the real-life performances of the similar kind of products.
These exercises provide an approximate idea about performance of the product/system to the design
team at the early stage of the product development. Based on the simulation studies, the designs can
be modified to achieve better performances. During the conventional design manufacturing process,
the design assessment is generally carried out after the production of first lot of the products. This

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consumes a lot of time, which leads to longer (in months/years) product development lead-time. Use
of CAD–CAE tools saves significant time in comparison with that required in the conventional
sequential design process.

CAD-CAE generated final designs are then sent to the production and process planning
section. Mechatronics based systems such as computer aided manufacturing (CAM): automatic
process planning, automatic part programming, manufacturing resource planning, etc. uses the
design data provided by the design team. Based these inputs, various activities will then be planned
to achieve the manufacturing targets in terms of quality and quantity with in a stipulated time frame.

Mechatronics based automated systems such as automatic inspection and quality assurance,
automatic packaging, record making, and automatic dispatch help to expedite the entire
manufacturing operation. These systems certainly ensure a supply better quality, well packed and
reliable products in the market. Automation in the machine tools has reduced the human intervention
in the machining operation and improved the process efficiency and product quality. Therefore it is
important to study the principles of mechatronics and to learn how to apply them in the automation
of a manufacturing system.

Control System
The output of the machine, mechanism or an equipment is maintained or altered accordance with the
desired manner is called the control system. Each element connected to the system has its own effect
on the output.

Definition of Control System

A control system is a system of devices or set of devices, that manages commands, directs or
regulates the behavior of other device(s) or system(s) to achieve desire results. In other words the
definition of control system can be rewritten as a control system is a system, which controls other
system. As the human civilization is being modernized day by day the demand of automation is
increasing accordingly. Automation highly requires control of devices. In recent years, control
systems plays main role in the development and advancement of modern technology and civilization.
Practically every aspects of our day-to-day life is affected less or more by some control system. A
bathroom toilet tank, a refrigerator, an air conditioner, a geezer, an automatic iron, an automobile all
are control system. These systems are also used in industrial process for more output. We find
control system in quality control of products, weapons system, transportation systems, power
system, space technology, robotics and many more. The principles of control theory are applicable
to engineering and non engineering field both.

Feature of Control System

The main feature of control system is, there should be a clear mathematical relation between
input and output of the system. When the relation between input and output of the system can be
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represented by a linear proportionality, the system is called linear control system. Again when the
relation between input and output cannot be represented by single linear proportionality, rather the
input and output are related by some non-linear relation, the system is referred as non-linear control
system.

Requirement of Good Control System

Accuracy
Sensitivity
Noise less
Stability
Bandwidth
Speed
Oscillation

Types of Control Systems

Open Loop Control System

A control system in which the control action is totally independent of output of the system then it is
called open loop control system. Manual control system is also an open loop control system. Figure shows
the block diagram of open loop control system in which process output is totally independent of controller
action.

Practical Examples of Open Loop Control System

1. Electric Hand Drier – Hot air (output) comes out as long as you keep your hand under the machine,
irrespective of how much your hand is dried.
2. Washing Machine – This machine runs according to the pre-set time irrespective of washing is
completed or not.
3. Bread Toaster - This machine runs as per adjusted time irrespective of toasting is completed or not.
4. Tea/Coffee Maker – These machines also function for pre adjusted time only.
5. Timer Based Clothes Drier – This machine dries wet clothes for pre – adjusted time, it does not
matter how much the clothes are dried.
6. Light Switch – lamps glow whenever light switch is on irrespective of light is required or not.
7. Volume on Stereo System – Volume is adjusted manually irrespective of output volume level.

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Advantages of Open Loop Control System

1. Simple in construction and design.
2. Economical.
3. Easy to maintain.
4. Generally stable.
5. Convenient to use as output is difficult to measure.

Disadvantages of Open Loop Control System

1. They are inaccurate.
2. They are unreliable.
3. Any change in output cannot be corrected automatically.

Closed Loop Control System

Control system in which the output has an effect on the input quantity in such a manner that
the input quantity will adjust itself based on the output generated is called closed loop control
system. Open loop control system can be converted in to closed loop control system by providing a
feedback. This feedback automatically makes the suitable changes in the output due to external
disturbance. In this way closed loop control system is called automatic control system. Figure below
shows the block diagram of closed loop control system in which feedback is taken from output and

fed in to input.

Practical Examples of Closed Loop Control System

1. Automatic Electric Iron – Heating elements are controlled by output temperature of the iron.
2. Servo Voltage Stabilizer – Voltage controller operates depending upon output voltage of the
system.
3. Water Level Controller– Input water is controlled by water level of the reservoir.

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4. Missile Launched & Auto Tracked by Radar – The direction of missile is controlled by
comparing the target and position of the missile.
5. An Air Conditioner – An air conditioner functions depending upon the temperature of the
room.
6. Cooling System in Car – It operates depending upon the temperature which it controls.

Advantages of Closed Loop Control System

1. Closed loop control systems are more accurate even in the presence of non-linearity.
2. Highly accurate as any error arising is corrected due to presence of feedback signal.
3. Bandwidth range is large.
4. Facilitates automation.
5. The sensitivity of system may be made small to make system more stable.
6. This system is less affected by noise.

Disadvantages of Closed Loop Control System

1. They are costlier.
2. They are complicated to design.
3. Required more maintenance.
4. Feedback leads to oscillatory response.
5. Overall gain is reduced due to presence of feedback.
6. Stability is the major problem and more care is needed to design a stable closed loop system.

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Comparison of Closed Loop and Open Loop Control System

Emerging areas of Mechatronics

Automation and robotics
Servo-mechanics
Sensing and control systems
Automotive engineering, automotive equipment in the design of subsystems such as anti-lock
braking systems
Computer-machine controls, such as computer driven machines like IE CNC milling machines
Expert systems
Industrial goods
Consumer products
Mechatronics systems
Medical Mechatronics, medical imaging systems
Structural dynamic systems
Transportation and vehicular systems
Mechatronics as the new language of the automobile
Computer aided and integrated manufacturing systems
Computer-aided design
Engineering and manufacturing systems

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Packaging
Microcontrollers / PLCs
Mobile apps
M&E Engineering

Sensors and Transducers

1. Sensor

It is defined as an element which produces signal relating to the quantity being measured.
Here, the output is usually an ‘electrical quantity' and measurand is a ‘physical quantity, property or
condition which is to be measured'. Thus in the case of a variable inductance displacement element,
the quantity being measured is displacement and the sensor transforms an input of displacement into
a change in inductance. Example piezo crystal, thermistor, solar cell

2. Transducer

It is defined as an element when subjected to some physical change experiences a related

change or an element which converts a specified measurand into a usable output by using a
transduction principle. It can also be defined as a device that converts a signal from one form to
another form. Example piezo crystal, thermometer, wiper, bourdon tube

Sensor Characteristics

Dynamic characteristics: The set of criteria defined for the instruments, which are changes
rapidly with time, is called ‘dynamic characteristics’. The various dynamics characteristics are:

i) Speed of response
ii) Measuring lag
iii) Fidelity
iv) Dynamic error

Speed of response: It is defined as the rapidity with which a measurement system responds to
changes in the measured quantity.

Measuring lag: It is the retardation or delay in the response of a measurement system to changes in
the measured quantity. The measuring lags are of two types:
a) Retardation type: In this case the response of the measurement system begins immediately after
the change in measured quantity has occurred.

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b) Time delay lag: In this case the response of the measurement system begins after a dead time after
the application of the input.

Fidelity: It is defined as the degree to which a measurement system indicates changes in the
measurand quantity without dynamic error.

Dynamic error: It is the difference between the true value of the quantity changing with time & the
value indicated by the measurement system if no static error is assumed. It is also called
measurement error

Static characteristics:

1 Range

The range of a sensor indicates the limits between which the input can vary. Thus, for example, a
thermocouple for the measurement of temperature might have a range of 25-225°C.

2 Span

The span is difference between the maximum and minimum values of the input. Thus, the above-
mentioned thermocouple will have a span of 200°C.

3 Error

Error is the difference between the result of the measurement and the true value of the quantity being
measured. A sensor might give a displacement reading of 29.8 mm, when the actual displacement
had been 30 mm, then the error is - 0.2 mm.

4 Accuracy

The accuracy defines the closeness of the agreement between the actual measurement result and a
true value of the measurand. It is often expressed as a percentage of the full range output or full–
scale deflection.

5 Sensitivity

Sensitivity of a sensor is defined as the ratio of change in output value of a sensor to the per unit
change in input value that causes the output change. For example, a general purpose thermocouple
may have a sensitivity of 41 µV/°C.

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6.Nonlinearity

Figure Non-linearity error

The nonlinearity indicates the maximum deviation of the actual measured curve of a sensor from the
ideal curve. Figure shows a somewhat exaggerated relationship between the ideal, or least squares
fit, line and the actual measured or calibration line. Linearity is often specified in terms of
percentage of nonlinearity, which is defined as:

Nonlinearity (%) = Maximum deviation in input ⁄ Maximum full scale input  

The static nonlinearity defined by above equation is dependent upon environmental factors,
including 

Nonlinearity (%) = Maximum deviation in input ⁄ Maximum full scale input  

The static nonlinearity defined by above equation is dependent upon environmental factors,
including temperature, vibration, acoustic noise level, and humidity. Therefore it is important to
know under what conditions the specification is valid.

7 Hysteresis

The hysteresis is an error of a sensor, which is defined as the maximum difference in output at any
measurement value within the sensor's specified range when approaching the point first with

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increasing and then with decreasing the input parameter. Figure shows the hysteresis error might
have occurred during measurement of temperature using a thermocouple. The hysteresis error value
is normally specified as a positive or negative percentage of the specified input range.

Figure Hysteresis error curve

8 Resolution

Resolution is the smallest detectable incremental change of input parameter that can be detected in
the output signal. Resolution can be expressed either as a proportion of the full-scale reading or in
absolute terms.For example, if a LVDT sensor measures a displacement up to 20 mm and it provides
an output as a number between 1 and 100 then the resolution of the sensor device is 0.2 mm.

9 Stability

Stability is the ability of a sensor device to give same output when used to measure a constant input
over a period of time. The term ‘drift’ is used to indicate the change in output that occurs over a
period of time. It is expressed as the percentage of full range output.

10 Dead band/ dead time

The dead band or dead space of a transducer is the range of input values for which there is no output.
The dead time of a sensor device is the time duration from the application of an input until the output
begins to respond or change.

11 Repeatability

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It specifies the ability of a sensor to give same output for repeated applications of same input value.
It is usually expressed as a percentage of the full range output:

Repeatability = (maximum – minimum values given) X 100/full range

12 Response time

Response time describes the speed of change in the output on a step-wise change of the measurand.
It is always specified with an indication of input step and the output range for which the response
time is defined.

Types of sensors

1. Potentiometeric Sensors

Figure shows the construction of a rotary type potentiometer sensor employed to measure the
linear displacement. The potentiometer can be of linear or angular type. It works on the principle of
conversion of mechanical displacement into an electrical signal. The sensor has a resistive element
and a sliding contact (wiper). The slider moves along this conductivity body acting as a movable
electric contact.

The object of whose displacement is to be measured is connected to the slider by using

 a rotating shaft (for angular displacement)
 a moving rod (for linear displacement)
 a cable that is kept stretched during operation

The resistive element is a wire wound track or conductive plastic. The track comprises of
large number of closely packed turns of a resistive wire. Conductive plastic is made up of plastic
resin embedded with the carbon powder. During the sensing operation, a voltage VS is applied across
the resistive element. A voltage divider circuit is formed when slider comes into contact with the
wire. The output voltage is measured as shown in the figure. The output voltage is proportional to
the displacement of the slider over the wire. Then the output parameter displacement is calibrated
against the output voltage VA.

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We know that the voltage at the output is,

VA = I RA
But the current is

Therefore 
As we know that R = ρL /A where ρ is electrical resistivity, L is length of resistor and A is area of
cross section

Applications of potentiometer

These sensors are primarily used in the control systems with a feedback loop to ensure that
the moving member or component reaches its commanded position.

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These are typically used on machine-tool controls, elevators, liquid-level assemblies, forklift
trucks, automobile throttle controls. In manufacturing, these are used in control of injection molding
machines, woodworking machinery, printing, spraying, robotics, etc. These are also used in
computer-controlled monitoring of sports equipment.

2. Strain Gauges

The electrical resistance strain gauge is a metal wire, Metal foil, or strip of semiconductor
material which is Wafer-like and cab be stuck onto surfaces Like a postage stamp. When subject to
strain, its resistance R changes, the fractional change in resistance del R / R being Proportional to the
strain, ie.

Where G is the constant of proportionality and is called as gauge factor. In general, the value of G is
considered in between 2 to 4 and the resistances are taken of the order of 100 Ω.

Figure A pattern of resistive foils

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Resistance strain gauge follows the principle of change in resistance as per the equation
above. It comprises of a pattern of resistive foil arranged as shown in above Figure. These foils are
made of Constantan alloy (copper-nickel 55-45% alloy) and are bonded to a backing material plastic
(polyimide), epoxy or glass fiber reinforced epoxy. As the work piece undergoes change in its shape
due to external loading, the resistance of strain gauge element changes. This change in resistance can
be detected by a using a Wheat stone’s resistance bridge as shown in Figure. In the balanced bridge
we can have a relation,

(2.2.6)

where Rx is resistance of strain gauge element, R2 is balancing/adjustable resistor, R1 and R3 are

known constant value resistors. The measured deformation or displacement by the stain gauge is
calibrated against change in resistance of adjustable resistor R2 which makes the voltage across
nodes A and B equal to zero.

Applications of strain gauges

Strain gauges are widely used in experimental stress analysis and diagnosis on machines and
failure analysis. They are basically used for multi-axial stress fatigue testing, proof testing, residual
stress and vibration measurement, torque measurement, bending and deflection measurement,
compression and tension measurement and strain measurement.

Strain gauges are primarily used as sensors for machine tools and safety in automotives. In
particular, they are employed for force measurement in machine tools, hydraulic or pneumatic press
and as impact sensors in aerospace vehicles.

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3. Capacitive element based sensor

Capacitive sensor is of non-contact type sensor and is primarily used to measure the linear
displacements from few millimeters to hundreds of millimeters. It comprises of two plates, in
between them a dielectric is placed. The dielectric may be air, mica, paper non conducting fluid etc.

The capacitance C of a parallel plate capacitor is given by,

where εr is the relative permittivity of the dielectric between the plates, εo permittivity of

free space,  A is the area of overlap between two plates and d the plate separation.

The capacitance of the capacitor is changed by three ways

1. Changing the area of the parallel plates

2. Change the distance between the plates
3. Change the dielectric constant

Figure shows the schematic of two-plate capacitive element sensor and displacement measurement
of a mechanical element..

Figure Displacement measurement using capacitive element sensor

For displacement changing the place separation, if the distance is increased the capacitance of the
capacitor is given by

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If three plate capacitor is used then ss the central plate moves near to top plate or bottom one due to
the movement of the element/workpiece of which displacement is to be measured, separation in
between the plate changes. This can be given as,

When C1 and C2 are connected to a bridge, then the resulting out-of-balance voltage would be in

proportional to displacement x.

By changing the area of overlap the resultant capacitance is given by

C = εεo L A / d

By changing the dielectric medium the capacitance is given by

C = (εεo + ε1 )(L A / d)

Capacitive elements can also be used as proximity sensor. The approach of the object
towards the sensor plate is used for induction of change in plate separation. This changes the
capacitance which is used to detect the object.

Applications of capacitive element sensors

• Small vessel pump control

• Grease level monitoring

• Level control of liquids

• Metrology applications

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4. Linear variable differential transformer (LVDT)

Figure Construction of LVDT sensor

Linear variable differential transformer (LVDT) is a primary transducer used for

measurement of linear displacement with an input range of about ± 2 to ± 400 mm in general. It has
non-linearity error ± 0.25% of full range. Figure shows the construction of a LVDT sensor. It has
three coils symmetrically spaced along an insulated tube. The central coil is primary coil and the
other two are secondary coils. Secondary coils are connected in series in such a way that their
outputs oppose each other. A magnetic core attached to the element of which displacement is to be
monitored is placed inside the insulated tube.

Figure Working of LVDT sensor

Principle of Operation and Working

As the primary is connected to an AC source so alternating current and voltages are produced in the
secondary of the LVDT. The output in secondary S1 is e1 and in the secondary S2 is e2. So the
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differential output is, eout = e1 - e2 This equation explains the principle of Operation of LVDT. Now
three cases arise according to the locations of core which explains the working of LVDT are
discussed below as,

CASE I When the core is at null position (for no displacement) When the core is at null position
then the flux linking with both the secondary windings is equal so the induced emf is equal in both
the windings. So for no displacement the value of output e out is zero as e1 and e2 both are equal. So it
shows that no displacement took place.

CASE II When the core is moved to upward of null position (For displacement to the upward of
reference point) In the this case the flux linking with secondary winding S 1 is more as compared to
flux linking with S2. Due to this e1 will be more as that of e2. Due to this output voltage eout is
positive.

CASE III When the core is moved to downward of Null position (for displacement to the downward
of reference point) In this case magnitude of e2 will be more as that of e1. Due to this output eout will
be negative and shows the output to downward of reference point.

Output VS Core Displacement A linear curve shows that output voltage varies linearly with
displacement of core.

Some important points about magnitude and sign of voltage induced in LVDT
 The amount of change in voltage either negative or positive is proportional to the amount of
movement of core and indicates amount of linear motion.
 By noting the output voltage increasing or decreasing the direction of motion can be
determined
 The output voltage of an LVDT is linear function of core displacement .

Advantages of LVDT
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 High Range - The LVDTs have a very high range for measurement of displacement.they can
used for measurement of displacements ranging from 1.25mm to 250mm
 No Frictional Losses - As the core moves inside a hollow former so there is no loss of
displacement input as frictional loss so it makes LVDT as very accurate device.
 High Input and High Sensitivity - The output of LVDT is so high that it doesn’t need any
amplification.the transducer posseses a high sensitivity which is typically about 40V/mm.
 Low Hysteresis - LVDTs show a low hysteresis and hence repeatability is excellent under all
conditions
 Low Power Consumption - The power is about 1W which is very as compared to other
transducers.
 Direct Conversion to Electrical Signals - They convert the linear displacement to electrical
voltage which are easy to process

Disadvantages of LVDT
 LVDT is sensitive to stray magnetic fields so they always require a setup to protect them
from stray magnetic fields.
 They are affected by vibrations and temperature.
It is concluded that they are advantageous as compared than any other inductive transducers.

Applications of LVDT sensors

 Measurement of spool position in a wide range of servo valve applications

 To provide displacement feedback for hydraulic cylinders
 To control weight and thickness of medicinal products viz. tablets or pills
 For automatic inspection of final dimensions of products being packed for dispatch
 To measure distance between the approaching metals during Friction welding process
 To continuously monitor fluid level as part of leak detection system
 To detect the number of currency bills dispensed by an ATM

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5. Eddy current proximity sensors

Figure Schematic of Inductive Proximity Sensor

Eddy current proximity sensors are used to detect non-magnetic but conductive materials.
They comprise of a coil, an oscillator, a detector and a triggering circuit. Figure shows the
construction of eddy current proximity switch. When an alternating current is passed thru this coil,
an alternative magnetic field is generated. If a metal object comes in the close proximity of the coil,
then eddy currents are induced in the object due to the magnetic field. These eddy currents create
their own magnetic field which distorts the magnetic field responsible for their generation. As a
result, impedance of the coil changes and so the amplitude of alternating current. This can be used to
trigger a switch at some pre-determined level of change in current.

Eddy current sensors are relatively inexpensive, available in small in size, highly reliable and have
high sensitivity for small displacements.

Applications of eddy current proximity sensors

 Automation requiring precise location

 Machine tool monitoring
 Final assembly of precision equipment such as disk drives
 Measuring the dynamics of a continuously moving target, such as a vibrating element,
 Drive shaft monitoring
 Vibration measurements

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6. Hall effect sensor

Figure shows the principle of working of Hall effect sensor. Hall effect sensors work on the principle
that when a beam of charge particles passes through a magnetic field, forces act on the particles and
the current beam is deflected from its straight line path. Thus one side of the disc will become
negatively charged and the other side will be of positive charge. This charge separation generates a
potential difference which is the measure of distance of magnetic field from the disc carrying
current. 

The typical application of Hall effect sensor is the measurement of fluid level in a container. The
container comprises of a float with a permanent magnet attached at its top. An electric circuit with a
current carrying disc is mounted in the casing. When the fluid level increases, the magnet will come
close to the disc and a potential difference generates. This voltage triggers a switch to stop the fluid
to come inside the container.

These sensors are used for the measurement of displacement and the detection of position of an
object. Hall effect sensors need necessary signal conditioning circuitry. They can be operated at 100

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kHz. Their non-contact nature of operation, good immunity to environment contaminants and ability
to sustain in severe conditions make them quite popular in industrial automation.

7.Resistance temperature detectors (RTDs)

RTDs work on the principle that the electric resistance of a metal changes due to change in
its temperature. On heating up metals, their resistance increases and follows a linear relationship as
shown in Figure. The correlation is

Where Rt is the resistance at temperature T (°C) and R0 is the temperature at 0°C and α is the

constant for the metal termed as temperature coefficient of resistance. The sensor is usually made to
have a resistance of 100 Ω at 0°C

Figure 2.5.2 Behavior of RTD materials [1]

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Figure Construction of a Resistance temperature detector (RTD)

Figure shows the construction of a RTD. It has a resistor element connected to a Wheatstone
bridge. The element and the connection leads are insulated and protected by a sheath. A small
amount of current is continuously passing though the coil. As the temperature changes the resistance
of the coil changes which is detected at the Wheatstone bridge.

RTDs are used in the form of thin films, wire wound or coil. They are generally made of
metals such as platinum, nickel or nickel-copper alloys. Platinum wire held by a high-temperature
glass adhesive in a ceramic tube is used to measure the temperature in a metal furnace. Other
applications are:

 Air conditioning and refrigeration servicing

 Food Processing
 Stoves and grills
 Textile production
 Plastics processing
 Petrochemical processing
 Micro electronics
 Air, gas and liquid temperature measurement in pipes and tanks
 Exhaust gas temperature measurement

8.Thermistors

Thermistors follow the principle of decrease in resistance with increasing temperature. The
material used in thermistor is generally a semiconductor material such as a sintered metal oxide
(mixtures of metal oxides, chromium, cobalt, iron, manganese and nickel) or doped polycrystalline
ceramic containing barium titanate (BaTiO3) and other compounds. As the temperature of
semiconductor material increases the number of electrons able to move about increases which results
in more current in the material and reduced resistance. Thermistors are rugged and small in
dimensions. They exhibit nonlinear response characteristics.

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Thermistors are available in the form of a bead (pressed disc), probe or chip. Figure shows the
construction of a bead type thermistor. It has a small bead of dimension from 0.5 mm to 5 mm
coated with ceramic or glass material. The bead is connected to an electric circuit through two leads.
To protect from the environment, the leads are contained in a stainless steel tube.

Figure Schematic of a thermistor

Applications of Thermistors

 To monitor the coolant temperature and/or oil temperature inside the engine
 To monitor the temperature of an incubator
 Thermistors are used in modern digital thermostats
 To monitor the temperature of battery packs while charging
 To monitor temperature of hot ends of 3D printers
 To maintain correct temperature in the food Handling and processing industry equipments
 To control the operations of consumer appliances such as toasters, coffee makers,
refrigerators, freezers, hair dryers, etc.

9.Thermocouple

Thermocouple works on the fact that when a junction of dissimilar metals heated, it produces
an electric potential related to temperature. When two wires composed of dissimilar metals are
joined at both ends and one of the ends is heated, then there is a continuous current which flows in
the thermoelectric circuit. Figure shows the schematic of thermocouple circuit. The net open circuit
voltage is a function of junction temperature and composition of two metals. It is given by,

ΔVAB = αΔT                                                                                            

Where α, the Seebeck coefficient, is the constant of proportionality.

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Figure Schematic of thermocouple circuit

Generally, Chromel(90% nickel and 10% chromium)–Alumel(95% nickel, 2% manganese, 2%

aluminium and 1% silicon) are used in the manufacture of a thermocouple. Table 2.5.1 shows the
various other materials, their combinations and application temperature ranges.

Applications of Thermocouples

 To monitor temperatures and chemistry throughout the steel making process

 Testing temperatures associated with process plants e.g. chemical production and petroleum
refineries
 Testing of heating appliance safety
 Temperature profiling in ovens, furnaces and kilns
 Temperature measurement of gas turbine and engine exhausts
 Monitoring of temperatures throughout the production and smelting process in the steel, iron
and aluminum industry

10.Light sensors
A light sensor is a device that is used to detect light. There are different types of light sensors
such as photocell/photo resistor and photo diodes being used in manufacturing and other industrial
applications.
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Photo resistor is also called as light dependent resistor (LDR). It has a resistor whose resistance
decreases with increasing incident light intensity. It is made of a high resistance semiconductor
material, cadmium sulfide (CdS). The resistance of a CdS photoresistor varies inversely to the
amount of light incident upon it.Photoresistor follows the principle of p hotoconductivity which
results from the generation of mobile carriers when photons are absorbed by the semiconductor
material.

Figure shows the construction of a photo resistor. The CdS resistor coil is mounted on a
ceramic substrate. This assembly is encapsulated by a resin material. The sensitive coil electrodes
are connected to the control system though lead wires. On incidence of high intensity light on the
electrodes, the resistance of resistor coil decreases which will be used further to generate the
appropriate signal by the microprocessor via lead wires.

Figure Construction of a photo resistor

Photoresistors are used in science and in almost any branch of industry for control, safety,
amusement, sound reproduction, inspection and measurement.

Applications of photo resistor

 Computers, wireless phones, and televisions, use ambient light sensors to automatically
control the brightness of a screen
 Barcode scanners used in retailer locations work using light sensor technology
 In space and robotics: for controlled and guided motions of vehicles and robots. The light
sensor enables a robot to detect light. Robots can be programmed to have a specific reaction if a
certain amount of light is detected.
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 Auto Flash for camera

 Industrial process control

11. Photo diodes

Photodiode is a solid-state device which converts incident light into an electric current.  It is
made of Silicon. It consists of a shallow diffused p-n junction, normally a p-on-n configuration.
When photons of energy greater than 1.1eV (the band gap of silicon) fall on the device, they are
absorbed and electron-hole pairs are created. The depth at which the photons are absorbed depends
upon their energy. The lower the energy of the photons, the deeper they are absorbed. Then the
electron-hole pairs drift apart. When the minority carriers reach the junction, they are swept across
by the electric field and an electric current establishes.

Photodiodes are one of the types of photo detector, which convert light into either current or
voltage. These are regular semiconductor diodes except that they may be either exposed to detect
vacuum UV or X-rays or packaged with a opening or optical fiber connection to allow light to reach
the sensitive part of the device.

Figure Construction of photo diode detector

Figure shows the construction of Photo diode detector. It is constructed from single crystal silicon
wafers. It is a p-n junction device. The upper layer is p layer. It is very thin and formed by thermal
diffusion or ion implantation of doping material such as boron. Depletion region is narrow and is
sandwiched between p layer and bulk n type layer of silicon. Light irradiates at front surface, anode,
while the back surface is cathode. The incidence of light on anode generates a flow of electron
across the p-n junction which is the measure of light intensity.

Applications of photo diodes

Camera: Light Meters, Automatic Shutter Control, Auto-focus, Photographic Flash Control

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Medical: CAT Scanners - X ray Detection, Pulse Oximeters, Blood Particle Analyzers

Industry

 Bar Code Scanners

 Light Pens
 Brightness Controls
 Encoders
 Position Sensors
 Surveying Instruments
 Copiers - Density of Toner

Safety Equipment

 Smoke Detectors
 Flame Monitors
 Security Inspection Equipment - Airport X ray
 Intruder Alert - Security System

Automotive

 Headlight Dimmer
 Twilight Detectors
 Climate Control - Sunlight Detector

Communications

 Fiber Optic Links

 Optical Communications
 Optical Remote Control

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Two mark questions in Unit 1

1. Define Mechatronics.

If an ideal mechanical system is controlled by electrical, electronics, control system engineering and
computer system then it is called Mechatronics system, and the technology is called Mechatronics.

2. What is a system? Give an example.

A system is a collection of physical components connected together to perform a desired task. A

system can be considered as a box, which has an input, and an output and the relationship between
the output and the input. Example: A motor may be thought of as a system, which has as its input
electric power and as output the rotation of a shaft.

3. What is a measurement system?

A measurement system can be considered as a black box, which is used for making measurements. It
has as its input the quantity being measured and its output the value of that quantity.

4. Write about transducer and sensor and give an example.

A transducer is a device that converts one form of energy to another. Usually a transducer converts

a signal in one form of energy to a signal in another. Examples: LED quartz, speaker etc
A sensor is a device which detects one form of energy and converts the data to electrical energy. A
microphone, thermocouple, LVDT are the good examples.

5. Write about the signal conditioner?

A signal conditioner takes the signal from the sensor and manipulates it in to a condition, which is
suitable for either display, or in the case of a control system, for use to exercise control.

6. What are the elements of the closed loop control system?

The various elements of a closed loop control system are,

a. Comparison element
b. Control element
c. Correction element
d. Process element
e. Measurement element

7. What are the two types of feedback loop?

The two types of feedback loop are,

a. Positive feedback loop, b. Negative feedback loop.

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"The feedback is said to be negative/positive feedback when the signal; which is feedback,
subtracts/adds from the input value. It is required to control a system. The control elements decide
what action to take when it receives an error signal"

8. What is mean by control system?

The output of the machine, mechanism or an equipment is maintained or altered accordance with the
desired manner is called the control system

9. What are the various elements of a closed loop system for a person controlling the
temperature?

The various elements of a closed loop system are,

1. Controlled variable 2. Comparison element 3. Error signal 4. Control unit 5. Measuring device

10. List some of the applications of Mechatronics?

1. Home Appliances: Washing machine, Bread machines, Dish washers, micro oven etc
2. Automobile: Electrical fuel injection, Antilock brake system, engine management system (EMS)
3. Aircraft: Flight control, Navigation system
4. Automated Manufacturing
5. Robot and CNC
6. Sorting and packaging system
7. Auto focus camera

11. What are the components of Mechatronics System?

1. input and outputs

2. Actuators and controllers
3. Sensors
4. Mechanical system
5. Micro processor, micro controllers and Programmable logic controllers

12. What is meant by a system in Mechatronics?

The System is the group of physical component combined to perform a specific function. Any
Mechatronics devices consists of systems or system is a box or a block diagram which has the input
and the output and has the relationship between the input and outputS

13. Draw the block diagram of measurement system.

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14. Obtain the basic functions of control systems.

1. To minimize the error between the actual and desired output

2. To minimize the time response to load changes in the system

15. What are the types of control system?

Open loop system, closed loop system

16. List down the requirements of control systems.

Stability, Accuracy, Response

17. Give an example for open loop system and closed loop systems.

1. Closed loop system – Automatic water level controller, pressure cooker, water heater, robot, CNC
etc
2. open loop system - Electric fan, traffic light, immersion heater etc

18. Compare open loop control system and closed loop control system.

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19. What are the advantages and disadvantages of Mechatronics system?

Advantages:
Accuracy, flexibility, reliability, less cost, compact in size, high speed of operation, easy to redesign
using programs

Disadvantages:
More maintenance cost, more initial cost, complex design

20. What is meant by measurement?

Measurement is an act or the result of comparison between the quantity and a predefined standard.

21. Explain the function of measurement system.

The measurement system consists of a transducing element which converts the quantity to be
measured in an analogous form. the analogous signal is then processed by some intermediate means
and is then fed to the end device which presents the results of the measurement.

22. Write the characteristics of the measurement system.

Characteristics of measurement system is divided into two categories:
i. Static characteristics
ii. Dynamic characteristics
47. Write the main static characteristics?
The main static characteristics are:
i. Accuracy
ii. Sensitivity
iii. Reproducibility
iv. Drift
v. Static error
vi. Dead zone
vii. Resolution

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viii. Precision
ix. Repeatability
x. Stability

23. Define static characteristics?

The static characteristics are the values given when the steady – state conditions occur. i.e., the
values given when the transducer has settled down after having received some input.

24. Define dynamic characteristics?

The dynamic characteristics refer to the behavior between the time that the input value changes and
the times that the value given by the transducer settles down to the steady – state value. Dynamic
characteristics are stated in terms of the response of the transducer to inputs in particular forms.
25. What are the terms that you can find from the dynamic characteristics?
1. Response time.
2. Time constant.
3. Rise time
4. Settling time.
26.. Define gauge factor.
The gauge factor is defined as the ratio of per unit change in resistance to per unit change in
length.
Gauge factor Gf= ∆R/R

27. What is the capacitance of a parallel plate capacitor?

The capacitance of a parallel plate capacitor is given by,
C = εA/d = εrεoA/d
Where
ε = Permitivity of the medium/m
εr = Relative permitivity
εo = Permitivity of the free space = 8.85x10-12F/m
A = Area of plates
D = Distance between two plates
28. Define LVDT?

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The Linear Variable Differential Transformer consists of three coils symmetrically spaced along
an insulated tube. The central coil is the primary coil and the other two are identical secondary
coils, which are connected in series in such a way that their outputs oppose each other.

29. Determine the working Principle of LVDT?

When there is an alternating voltage input to the primary coil, alternating e.m.f.s are induced
in the secondary coils. With the magnetic core central, the amount of magnetic material in
each of the secondary coil is the same.
30. What are the uses of LVDT?
The uses are as follows.
a. Widely used as primary transducers for monitoring displacements.
b. Also used as secondary transducers in the measurement of force, weight and pressure.

31. Write about inductive proximity switch?

Inductive proximity switch consists of a coil wound round a core. When the end of the coil is
close to a metal object is inductance changes. This change can be monitored by its effect on a
resonant circuit and the change used to trigger a switch. It can only be used for the detection of
metal objects and is best with ferrous metals.

32. Write about Hall effect sensors?

When a beam of charged particles passes through a magnetic field, forces act on the particles and
the beam is deflected from its straight line path. A current flowing in a conductor is like a beam
of moving charges and thus can be deflected by a magnetic field.
33. What is Hall co-efficient?
The transverse potential difference is given by, V = KHBI
Where, b
KH = Hall co-efficient
B = Magnetic flux density at right angles to the plate,
I = Current

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