2. Books
References:
1. Robert H. Bishop. Editor-in-chief. “The Mechatronics Handbook”, CRC Press, with
ISA–The Instrumentation, Systems, Automation Society (50 Chapters), 2002. ISBN: 0-
8493-0066-5 44
2. G. Webster. Editor-in-chief. “Measurement, Instrumentation, and Sensors
Handbook” CRC Press. 1999. 0-8493-2145-X.
3. Dan S. Necsulescu, Mechatronics, Prentice Hall, 2002, (311 p.). ISBN: 0-201-44491-7
4. VICTOR GIURGIUTIU and SERGEY EDWARD LYSHEVSKI.
“MICROMECHATRONICS - Modeling, Analysis, and Design with MATLAB”. CRC
PRESS, Boca Raton London New York Washington, D.C. (ISBN: 0-8493-1593-X).
2004.
2 September 2023
3. Chapter one
Introduction to Mechatronics
CHAPTER
Ketema Bobe
Department of Mechanical Engineering
2 September 2023
5. What is Mechatronics?
Mechatronics is the synergistic combination of mechanical
engineering (“mecha” for mechanisms), electronic engineering
(“tronics” for electronics), and software engineering.
Mechatronics is the field of study concerned with the design,
selection, analysis and control of systems that
mechanical elements with electronic components,
combine
including
computers &/or microcontrollers.
The mechatronics field is not simply the
sum of these three major areas, but rather the
field defined as the intersection of these
areas when taken in the context of systems
design.
Mechatronics may alternatively be referred to as “electromechanical
systems.” 5
2 September 2023
7. Historical Background
Mechatronics: a concept of Japanese origin, 1970’s. This concept
applicable in 1980’s to produce industrial robots.
The Japanese were the first to recognize the limitations of
traditional mechanical engineering and introduced the term
“Mechatronics” to mean an integrative multidisciplinary approach
for design of mechanical systems and processes.
Virtually every modern electromechanical system has an
embedded computer controller. Therefore, computer hardware and
software issues (in terms of their application to the control of
electromechanical systems) are part of the field of mechatronics.
7
2 September 2023
8. Evolution of Mechtronic Systems
The development of mechatronics has gone through three stages.
The first stage corresponds to the years when this term was
introduced. During this stage, technologies used in mechatronics
systems developed rather independently and individually.
During the second stage, i.e., with the beginning of the eighties, a
synergistic integration of different technologies started taking
place. For example: Optoelectronics (i.e. an integration of optics
and electronics). The concept of hardware/software co-design also
started in those years.
The third and the last stage can also be considered as the
beginning of the mechatronics age since early nineties.
8
2 September 2023
9. Contd…
Important achievement of the third stage
Increased use of computational intelligence in mechatronic
products and systems. It is due to this development that we
can now talk about Machine Intelligence Quotient (MIQ).
It is the possibility of miniaturization of components; in the
form of micro actuators and micro sensors (i.e. micro
mechatronics).
9
2 September 2023
11. Significance of Mechatronics
The purpose of this interdisciplinary engineering field is
Ability to increase competitiveness of the product
through use of technology.
It automata from an engineering perspective.
It control advanced hybrid systems
Support and enable development of new product
High levels of precision and reliability (Enhance existing
products)
11
2 September 2023
12. Characteristics of Mechatronic Systems
Since Mechatronics is not just a marriage of electrical and
mechanical systems and is more than just a control system; it is a
complete integration all of them,
They are generally complex systems with high levels of
integration.
They have more functionality than conventional systems.
Functionality is transferred from the mechanical to the
electronic and software domain.
They are based on the development of some of real-time
system architecture, often involving distributed and devolved
intelligence.
Operation at the system level is generally transparent to the
user.
12
2 September 2023
13. The Why of Mechatronics
Mechatronics system designs can often leads to
L
„ow volume
M
„ore variety „
Lower cost of production
H
„igher levels of flexibility
Reduced lead time in manufacture „
Automation in manufacturing and assembly
Lower maintenance cost
13
2 September 2023
17. Contd…
An office copy machine consists of analog and digital
circuits, sensors, actuators and microprocessors.
Analog circuits control the lamp, heater and other power
circuits in the machine.
Digital circuits controls the digital displays, indicator
lights, buttons and switches forming the user interface.
Optical sensors and micro switches detects the presence
or absence of the paper, its proper positioning and
whether or not doors and latches are in their correct
positions.
17
2 September 2023
18. Contd…
include encoders used to track the motor
Other sensors
rotation.
Actuators include servo and stepper motors that load and
transport the paper, turn the drum and index the sorter.
Microprocessors coordinate all the functions in the machine
Scanner
Computer
disk drive
Exhibits quick response,
precision, and robustness
Fax
Photocopy
machine
18
2 September 2023
24. Contd…
a)Vehicle application area
Safety
Airbag system
Anti-lock breaking system
Electronic stability controls
Comfort
Door locks
Key less entry system
Heating system controls
Seat positioning controls
Power train
Engine control
Fuel pump control
Fuel sensing controls
Gearbox controls
24
2 September 2023
26. Contd…
b)High Speed Trains
•Train Position and Velocity
JR-Maglev
Top Speed: 574 km/h (357
mph) Country: Japan
constantly monitored from
main command center.
•Error margin in scheduling
no more than 30 seconds
•Fastest trains use magnetic levitation
Transrapid
Top Speed: 550 km/h (340
mph) Country: German
Magnetic Levitation
26
2 September 2023
27. Contd…
Advantages
•Simple and intuitive personal transportation
device
c) Segway
Systems Uses
•Tilt and pressure sensors
•Microcontroller
•Motors
•Onboard power source
27
2 September 2023
32. Contd…
Vacuum cleaner
Assisting solders in combat fields
Delivering food and medicine in hospitals
Operate in unstructured environments
Wheelchair
Vacuum cleaner
Obstacle avoiding mobile
robot
32
2 September 2023
37. Contd…
• Fully automated bending: load sheet metal and the finished
bent parts come out
• Can bend complex shapes
a) CNC Bending
37
2 September 2023
41. Contd…
System Can
•Carry 340 lb
•Run 4 mph
•Climb, run, and walk
•Move over rough terrain
BigDog
Advantages
•Robot with rough-terrain mobility that
could carry equipment to remote location.
41
2 September 2023
43. Contd…
System Can
•Collect specimens
•Has automated onboard lab for
testing specimens
Advantages
•Robot that can travel to other
planets and take measurements
automatically.
Phoenix Mars Lander's
43
2 September 2023
45. Contd…
•Used by patients with slow or erratic
heart rates. The pacemaker will set a
normal heart rate when it sees an
irregular heart rhythm.
•Monitors the heart. If heart fibrillates
or stops completely it will shock the
heart at high voltage to restore a
normal heart rhythm.
Pace Maker
Implantable Defibrillation
45
2 September 2023
47. Contd…
System Uses
•Proximity sensors
•Control circuitry
•Electromechanical valves
•Independent power source
Advantages
•Reduces spread of germs by making
device hands free
•Reduces wasted water by automatically
turning off when not in use
47
2 September 2023
48. Contd…
Advantages
• Reduces spread of germs by making device
hands free
• Reduces wasted materials by controlling how
much is dispensed
Systems Uses
•Motion sensors
•Control circuitry
•Electromechanical actuators
•Independent power source
Soap Dispenser
Paper Towel Dispenser
48
2 September 2023
49. Basic Elements of Mechatronics System
system is an integration of the
Generally any Mechatronic
following major components:
Sensors
Actuator
Controller
The control logic
Signal Processing
49
2 September 2023
50. Design of mechatronic systems
Stages in design process
The need
Analysis of problem
Preparation of Specification
Generation of possible solutions
Selection of a suitable solution
Production of a detailed design
Production of working drawings
50
2 September 2023
51. Contd…
Advantages of mechatronics design
High resolution and accuracy
Reduces house hold heating cost
Self calibrating
Flexible design
Environmental friendly
51
2 September 2023
53. Sensors and Actuators
Contents
Sensor and transducer
Terminologies
Displacement, position and proximate
Velocity and motion
Force and fluid pressure
Liquid flow and level
Temperature
Light sensor
Selection of sensor
Inputting data by switches
53
2 September 2023
54. /
Sensors and Transducer
69
is a device that produces an output signal for the purpose of
sensing of a physical phenomenon.
It is used for an input device that provides a usable output in
response to a specified physical input.
For example, a thermocouple is a sensor that converts a temperature
difference into an electrical output.
is a device that converts a signal from one form to a
different physical form.
It is a device that converts one type of energy to another.
Energy types include (but are not limited to) electrical,
mechanical, electromagnetic (including light), chemical,
2 September 2023
55. Terminologies
generally
filtering,
includes
electrical
a front-end preprocessing, which
functions such as signal amplification,
isolation, and multiplexing.
In addition, many transducers require excitation currents or
voltages, bridge completion, linearization, or high amplification
for proper and accurate operation.
Charge amplifiers, lock-in amplifiers, power amplifiers,
switching amplifiers, linear amplifiers, tracking filters, low-
pass filters, high-pass filters, and notch filters are some of the
signal-conditioning devices used in mechatronics systems.
55
Chapter 2, Dr. Besufekad Negash
2 September 2023
56. Contd…
- it is the limits between which the input can vary.
For example – Load cell for the measurement of forces might have
a range of 0-50 kN.
- the difference between the result of the measurement and the
true value of the quantity being measured.
Error= Measured value – True value
- is the extent to which the value indicated by a
measurement system might be wrong. It is the summation
of all possible errors that are likely to occur, as well as
the accuracy to which the transducer has been calibrated.
For Example – A sensor might be specified as having an accuracy of
+5% of full range output. Given: Temp Range 0-200 °C. Reading could be
within + 10 °C of the true reading.
56
2 September 2023
57. Contd…
- is the relationship indicating how much output you get
per unit input, ie. Output/input.
For example: A resistance thermometer may have sensitivity of 0.5
ohms/ °C
Sensitivity is the ability of the measuring instrument to respond to
changes in the measured quantity. It is also the ratio of the change of
output to change of input.
57
2 September 2023
58. Contd…
Hysteresis Error
The error of a measurement is the difference between the result of
the measurement and the true value of the quantity being measured.
- is the maximum difference in output for increasing
and decreasing values.
Hysteresis is an error caused by when
the measured property reverses
direction, but there is some finite lag in
time for the sensor to respond, creating
a different offset error in one direction
than in the other.
58
2 September 2023
59. Contd…
Fig. Some source of error: (a) Nonlinearity and (b) Hysteresis
59
The error associated in the deviation from linearity between the
input and the output. The error is quoted as the percentage of the
full range output.
Nonlinearity and hysteresis
2 September 2023
60. Contd…
the repeatability of the transducer is its ability to give
the same output for repeated applications of the same
input value.
For example: Angular velocity => repeatability + 0.01% of the full
range at a particular angular velocity.
the ability to give the same output when used to
measure a constant and is measured on a number of
occasions.
the stability of a transducer is its ability to give the same
output when used to measure a constant input over a
period of time.
60
2 September 2023
61. Contd…
is often used to describe the change in output that occurs over
time.
The drift expressed as a percentage of the full range output.
The term zero drift is used for the changes that occur in
output when there is zero input.
is the range of input values for which
there is no output.
For example: bearing friction in a flow meter using a rotor might
mean that there is no output until the input has
reached a particular velocity threshold.
61
2 September 2023
62. Contd…
The resolution of a sensor is the smallest change it can
detect in the quantity that it is measuring.
The resolution is related to the precision which the
measurement is made.
For example: a scanning tunneling probe (a fine tip near a surface
collects an electron tunneling current) can resolve
atoms and molecules
62
2 September 2023
63. Sensors and transducers
Displacement, position and proximity
Potentiometer
Strain-gauged element
C
„apacitive element „
Linear variable differential transformers „
Eddy current proximity sensors „
Inductive proximity switch
Optical encoders
P
„neumatic sensors
P
„roximity switches (magnetic)
Hall effect sensors
63
2 September 2023
65. Sensors
L
„iquid level „
Floats „
Differential pressure
Temperature
B
„imetallic strips „
Resistance temperature detectors „
Thermistors „
Thermo-diodes and transistors „
Thermocouples
Light sensors
P
„hoto diodes
Photo resistors
P
„hoto transistor
93
2 September 2023
66. Contd…
Displacement sensor- is measure the distance between the present
position of the target and the previously
recorded position.
- how much the object has been moved
Position sensor- is used for a sensor that gives a measure of the
distance between a reference point and the
current location of the target
- position of an object with a reference point
Proximity- Form of position sensors, it detects when an object has
moved
66
2 September 2023
68. Contd…
Two groups
Linear
Angular
Linear displacement sensors might be used to monitor the
thickness or other dimensions of sheet materials, separation of
rollers, the position or presence of a part, the size of a part.
Angular displacement methods might be used to monitor the
angular displacement of shafts.
68
2 September 2023
70. Contd…
Two basic types of displacement / position sensor:-
1. Contact devices
• Limit switches
• Resistive position transducers
2. Non-contact devices
• Magnetic sensors, including Hall effect and magneto-resistive
sensors
• Ultrasonic sensors
• Proximity sensors
• Photoelectric sensors
70
2 September 2023
71. Measuring Displacement
99
• With the supply voltage (Vs), the output voltage (V
o) will vary
between zero and the supply voltage.
• Displacement is measured based on potential difference
•„Plastic resin embedded with carbon powder
• Potentiometers are very common devices used to measure
displacement. A linear potentiometer is used for linear measurements
and an angular potentiometer is used for angular measurements.
• The linear potentiometer is a device in which the resistance varies as a
function of the position of a slider, shown below.
2 September 2023
72. Contd…
• It should be noted that the device measuring Vo must have a high
impedance to maintain a linear response and avoid loading error.
•Linear potentiometers can be used to measure displacements as
small as 0.1 to 0.2 in. (2.5 to 5 mm) up to displacements of more than
1 ft.
72
2 September 2023
74. Contd…
The electrical resistance strain gauge is a metal wire, metal foil strip, or
a strip of semiconductor material which is wafer like and can be stuck
into surfaces like a postage stamp.
When subject to strain, its resistance R changes, the fractional change
in resistance ∆R/R being proportional to the strain E, that is
∆R/R=GE
Where G, the constant of proportionality, is termed as the gauged
factor.
The resistance change of a strain gauge is a measurement of the change
in length of the element to which the strain gauge is attached
74
2 September 2023
75. Contd…
Electric-resistance strain gauge
Metal wire, metal foil strip, a strip of semiconductor material
„
∆R/R= Gε
G = constant of proportionality, Gauge factor
G
„ = 2, Calibration based on actual experiments „
Constantan alloy: copper-nickel (55-45%) alloy
75
2 September 2023
76. Contd…
Example: An electrical resistance of 100 ohms and a gauge factor of
2.0. What is the change of resistance ΔR of the gauge
when it is subject to a strain of 0.001.
Answer:
ΔR = R×G × strain
ΔR =100×2.0×0.001
ΔR =0.2 ohms
76
2 September 2023
77. Contd…
Strain gauges
• „Deflection or deformation of flexible
elements
• Attach to flexible elements „viz.
cantilevers, pipes, U shaped elements
• „Linear displacement in the order of 1 to
30 mm
•„Nonlinearity error 1% of the full range
77
2 September 2023
79. Contd…
Monitoring of displacement „
Non-contact type displacement
sensor
C
„= (εrεoA)/d
ε
„r= relative permittivity of
dielectric between the plates
ε„o=permittivity of free space
„
A
= area of overlap „
d = plate separation
Example: T
„
ouch-screen: Apple „
79
2 September 2023
80. Contd…
Fig. a Capacitive proximity sensor detects a change
in capacitance incurred by the presence of a seal ring
target
80
Fig. Presence of the metal target reduce the metal target
reduces the effective distance between electrodes (by the
factor t), resulting in an increase in capacitance.
2 September 2023
81. Contd…
It is a mechanical displacement transducer.
It gives an a.c. voltage output proportional to the distance of the
transformer core to the windings.
The LVDT is a mutual-inductance device with three coils and a core An
external a.c. power source energizes the central coil and the two-
identical secondary coils connected in series in such a way that their
outputs oppose each other.
81
2 September 2023
82. Contd…
Fig. LVDT 82
A magnetic core is moved through the central tube as a result of
displacement being monitored. However when the core is displaced
from the central position there is a greater amount of magnetic core
in one coil than the other.
A greater displacement means even more core in one coil than the
other, the output, the difference between the emf increases, the
greater the displacement being monitored.
2 September 2023
83. Contd…
A greater displacement means even more core in one coil than the
other, the output, the difference between the emf increases, the
greater the displacement being monitored.
83
2 September 2023
84. Contd…
Primary transducer „
Operating range ±2 to ±400 mm „
Non-linearity error ±0.25% of
full range „
Absolute position sensor „
Good repeatability and
reproducibility „
Highly reliable
N
„on-contact, no friction or
sliding „
Completely sealed „
Servomechanisms, automated
measurement in machine tools „
Works with phase sensitive
demodulator and low pass filter
84
2 September 2023
85. Contd…
Detection of non-magnetic conductive material
Relatively inexpensive
Small in size
High reliability
High sensitivity for small displacements
85
2 September 2023
86. Contd…
Coil wound on acore
close to a metallic object
inductance changes metallic object
inductance changes
monitored by a resonant circuit
triggers a switch
Detection of metallic objects
86
2 September 2023
87. Contd…
An encoder is a device that provides digital output as a result of
linear and angular displacement.
Position encoders are of two types:
1.Incremental
2.Absolute
Incremental encoders : Detect changes in rotation from some datum
while the absolute encoders give the actual angular position.
Absolute encoder
Incremental encoder
87
2 September 2023
88. Contd…
Digital output as result of linear / angular displacement angular
displacement
Number of pulses proportional to angular displacement
Angular position = number of pulses from the datum position
Sequential output of the sensor = No in the binary code
88
2 September 2023
90. Contd…
Micro switches: electrical contact type switches
Conveyor belts
Reed switch: non-contact magnetic switch
Widely used in checking the closure of doors
Can be used with tachometers Reed Switch
Lever operated Roller operated Cam operated
Output : on or off
90
2 September 2023
91. Contd…
„When a beam of charge particles
passes through a magnetic field,
forces act on the particles and
the beam is deflected from its
straight line path.
91
2 September 2023
92. Contd…
Displacement, position a well as proximity detection „
Needs necessary signal conditioning circuitry
A
„dvantages
C
„an be operated at 100 kHz „
Non-contact „
Immune to environment contaminants „
Can be used under severe conditions
92
2 September 2023
93. Contd…
This can be used for measuring angular velocity, number of pulses
produced per second being determined.
Used to measure angular velocity. It is essentially a small electric
generator, consisting of coil mounted in magnetic field .when the coil
rotates an alternating emf is induced in the coil, the size of the
maximum emf being a measure of the angular velocity. when used
with a commutator a dc output can be obtained which is a measure of
the angular velocity.
93
2 September 2023
95. Contd…
L
„ithium tantalate, crystal material
Generates charge in response to heat
flow „
Material > heat + electric field >
electrical dipoles line up > polarization>
retains the polarization after cooling „
Such polarized material > infrared
radiation > rise in temp > reduces the
polarization „
Pyroelectric sensor
polarized material +
= pyroelectric
thin metal film
electrodes on opposite faces
∆q= kp∆T 95
2 September 2023
96. Contd…
Force: The measurement of the interaction between bodies.
The most commonly used sensors are generally based on either
piezoelectric quartz crystal or strain gage sensing elements.
Technology Fundamentals
Quartz force sensors suited for the measurement of dynamic
oscillating forces, impact, or high speed compression/tension
forces.
The basic design utilizes the piezoelectric principle, where applied
mechanical stresses are converted into an electrostatic charge that
accumulates on the surface of the crystal.
96
2 September 2023
97. Contd…
Devices to measure these small changes in dimensions are called
strain gages.
Strain Gauge Load Cell –use of electrical resistance to monitor the
strain produced in some member when stretched, compressed or bent.
S
„pring balance
S
„train gauge load cell
Electrical resistance „
Forces up to about 10 MN „
Non-linearity error ±0.03%
Repeatabilityerror±002
97
2 September 2023
98. Contd…
Technology Fundamentals
Sensors based on foil strain gage
technology are ideally designed for the
precise measurement of a static weight or
force.
The applied input is translated into a
voltage by the resistance change in the
strain gauges.
The amount of change in resistance
indicates the magnitude of deformation in
the transducer structure and hence the load
that is applied.
98
2 September 2023
99. Contd…
a) Metal wire b) Metal foil c) Semiconductor
A strain gauge, a device whose electrical resistance varies in
proportion to the amount of strain in the device. The most widely
used gauge is the bonded metallic strain gauge. 99
2 September 2023
100. Contd…
Two common arrangements of the three strain gages are:
Rectangular rosette
Equiangular rosette
In rectangular rosette, the gages are placed at angles of 0, 45 and
90 degrees.
In equiangular rosette, the gages are arranged at 0, 60 and 120
degrees.
100
2 September 2023
101. Contd…
In industrial processes, chemical
petroleum, power industry
E
„lastic deformation of diaphragms,
capsules, bellows „
Absolute pressure measurement
Use of strain gauges „
S
„ilicon diaphragms with doped
strain gauges Capsule (more sensitive
than diaphgm)
Bellows
Flat diaphragm
101
Corrugated diaphragm
2 September 2023
102. Contd…
Stretched or compressed generates electric charge > voltage „
Ionic crystals
q = kx= SF „
Measurement of forces, pressure, acceleration
102
2 September 2023
104. Contd…
Based on measurement of pressure
drop „
Quantity of fluid flow is proportional
to square root of pressure difference
O
„rifice plate : simple, cheap with no
moving parts „
Does not work with slurries „
Accuracy ±1.5%, nonlinear „
Turbine meter: multi bladed rotor
and a magnetic pick-up „
Accuracy ±0.3%, expensive
104
2 September 2023
105. Contd…
D
„ irect method : monitoring the
position of liquid surface, floats „
Indirect method : measurement of
some variable related to the height,
weight, pressure difference
105
2 September 2023
107. Contd…
Mixtures of metal oxides, chromium, cobalt, iron, manganese and
nickel : semi conductors „
Resistance decreases in a very nonlinear manner with increase in
temperature „
Largechange in resistance per degree change in temperature
Highly nonlinear
107
2 September 2023
108. Contd…
T
„wo metals held together, potential difference (PD) occurs at the
junction
PD depends upon metals and temperature „
Complete circuit involving two junctions „
Reference junction 0⁰C (Ice and water)
Compensation circuit, to compensate emf by dropping voltage
across a resistance thermometer element „
Use of sheath, low response time
108
2 September 2023
109. Selection of sensors
Nature of measurement required „
Variable V
„ariable „
Nominal value „
Range
Accuracy
Speed „
Reliability
Environmental conditions
Nature of output, decides signal conditioning requirement „
Maintainability L
„ife L
„ife „
Power supply requirements „
Ruggedness „
Availability „
Cost
109
2 September 2023
111. • Signal conditioning circuits are used to process
the output signal from sensors of a measurement
system to be suitable for the next stage of
operation
112.
113. The sensing element converts the non-electrical signal (e.g.
temperature) into electrical signals (e.g. voltage, current,
resistance, capacitance etc.).
The job of the signal conditioning element is to convert the
variation of electrical signal into a voltage level suitable for
further processing.
The next stage is the signal processing element.
It takes the output of the signal conditioning element and
converts into a form more suitable for presentation and
other uses (display, recording, feedback control etc.).
Analog-to-digital converters, linearization circuits etc. fall
under the category of signal processing circuits.
114. • The success of the design of any measurement
system depends heavily on the design and
performance of the signal conditioning circuits.
• Even a costly and accurate transducer may fail to
deliver good performance if the signal conditioning
circuit is not designed properly.
• Nowadays, many commercial sensors often have in-
built signal conditioning circuit.
• This arrangement can overcome the problem of
incompatibility between the sensing element and the
signal conditioning circuit.
115.
116. The function of the signal conditioning circuits
include the following items:
Signal amplification
Filtering
Interfacing with Data Acquisition (ADC)
Protection(Zener & photo isolation),
Linearization,
Current – Voltage change circuits,
Resistance change circuits (Wheatstone bridge),
Error compensation
120. Filtering
we can also use filters to reject unwanted noise within a certain
frequency range.
Many systems will exhibit 60 Hz periodic noise components from
sources such as power supplies or machinery.
Many signal conditioners include low pass noise filters
to remove unwanted noise, an extra precaution is to use
software averaging to remove additional noise.
121. Low pass filters on our signal conditioning circuitry can
eliminate unwanted high-frequency components.
However, be sure to select the filter bandwidth carefully so
that we do not affect the time response of our signals.
Software averaging is a simple and effective technique of
digitally filtering acquired readings; for every data point
you need, the Data Acquisition (DAQ) system acquires and
averages many voltage readings.
For example, a common approach is to acquire 100 points
and average those points for each measurement you need.
For slower applications in which you can oversample in
this way, averaging is a very effective noise filtering
technique.
122.
123.
124. Operational Amplifiers
Many sensors develop extremely low-level output signals.
The signals are usually too small for applying directly to
low-gain, multi flexed data acquisition system inputs, so
some amplification is necessary.
Two common examples of low-level sensors are
thermocouples and strain-gage bridges that typically deliver
full-scale outputs of less than 50 Mv
125. Amplification
Unwanted noise can play havoc with the measurement
accuracy of system.
The effects of system noise on the measurements can be
extreme if we are not careful.
An amplifier, located directly on the in external signal
conditioners and can apply gain to the small signal before
the Analogue to Digital Converter (ADC) converts the
signal to a digital value.
Boosting the input signal uses as much of the ADC input
range as possible.
126. Isolation
Improper grounding of the DAQ system is the most common
cause of measurement problems and damaged DAQ boards.
Isolated signal conditioners can prevent most of these problems
by passing the signal from its source to the measurement device
without physical connection.
Isolation breaks ground loops, rejects high common-mode
voltages, and protects expensive DAQ instrumentation.
Common methods for circuit isolation include using optical,
magnetic, or capacitive isolators.
127. Magnetic and capacitive isolators modulate the signal to convert
it from a voltage to a frequency.
The frequency can then be transmitted across a transformer or
capacitor without a direct physical connection before being
converted back to a voltage value.
When you connect your sensor or equipment ground to your
DAQ system, you will see any potential difference in the
grounds on both inputs to your DAQ system.
This voltage is referred to as common-mode voltage.
Most data acquisition systems use a number of different types of
circuits to amplify the signal before processing.
128. Modern analog circuits intended for these data acquisition
systems comprise basic integrated operational amplifiers,
which are configured easily to amplify or buffer signals.
Integrated operational amplifiers contain many circuit
components, but are typically portrayed on schematic
diagrams as a simple logical functional block.
A few external resistors and capacitors determine how they
function in the system.
Their extreme versatility makes them the universal analog
building block for signal conditioning.
130. M e c h a n i c a l a c t u a t i o n s y s t e m
Mechanical system involving:
Linkages
Cams
Gears
ratchet and pawl
belt and chain drives
131. Cont.…
Provide function as:
Motion converters
rotational to linear
Force amplification
lever
Change of speed
• gears
Transfer of rotation axis
timing belt
Particular types of motion
quick return mechanism, cam
132. Types of motion
Translational, rotational and its combination
Degree of freedom, dof
dof = 6 – number of constrain
Cont.…
133. Ty p e s o f m o t i o n
Translational, rotational and its combination
Degree of freedom, dof
dof = 6 – number of constrain
For planar
dof = 3(N-1) – 2L
where:
N = number of link
L = number of join
Cont.…
134. Kinematic chains
A link is part of a mechanism
A joint is a connection between link
Kinematic chain is a sequence of
link and joints
Cont.…
135. K i n e m a t i c c h a i n s
Open loop kinematic chain
Cont.…
136. K i n e m a t i c c h a i n
Slider crank mechanism
Cont.…
137. K i n e m a t i c c h a i n
The four bar chain
Grashoff theorem
Lmax + Lmin less than or equal to La + Lb
for one link to rotate 360 deg
Double crank
Double lever Lever crank
Cont.…
142. G e n e v a w h e e l
Lower Wheel
Upper Wheel
Upper wheel axis of rotation
Lower wheel axis of rotation
Driving pin
Mechanism is used for achieving intermittent motions.
The component has two wheels; upper & lower
Continuous rotational movement of the lower wheel
Intermittent motion of the upper wheel; rotates step-wise
143. G e a r t r a i n s
Used to change speed or torque of rotating device
Cont.…
144. G e a r t r a i n s
Used to change speed or torque of rotating device
Cont.…
145. G e a r t r a i n s
• G = A / B = dB / dA= B / A
G = A / B x B / C = A / C
Cont.…
146. Epycylic gear train
Consists of groups of gears
3 possibility of gear ratios
Cont.…
147. Ratchet and pawl
Used to lock a mechanism when its holding a load
Cont.…
148. B e l t a n d c h a i n d r i v e s
Torque on A, A = (T1 - T2) rA
Torque on B, B = (T1 - T2) rB
Power = (T1 - T2)v
–where belt speed v = A rA
Cont.…
149. B e l t a n d c h a i n d r i v e s
Reversing drive
Cont.…
150. STATIC CHARACTERISTICS OF DEVICE
As mentioned earlier, the static characteristics are defined
for the instruments which measure the quantities which do
not vary with time.
The various static characteristics are :-
1. ACCURACY
2. PRECISION
3. RESOLUTION
4. ERROR
5. SENSITIVITY
6. THRESHOLD
7. REPRODUCIBILITY
8. ZERO DRIFT
9. STABILITY
10.LINEARITY
151. 1. Accuracy
It is the degree of closeness which the instrument reading approaches to
true value of the quantity to be measured.
It denotes the extent to which we approach the actual value of the quantity.
It indicates the ability of instrument to indicate the true value of the quantity.
The accuracy can be expressed in the following ways
i. Accuracy as Percentage of Full Scale Reading:
In case of instruments having uniform scale, the accuracy can be expressed
as percentage of full scale reading.
E.g. The accuracy of an instrument having full scale reading of 50 units may
be
expressed as ± 0.1 % of full scale reading. From this accuracy indication,
practically
accuracy is expressed in terms of limits of error. So for the accuracy limits
specified above, there will be ± 0.05 units error in. any measurement
ii. Accuracy as Percentage of True Value:-
This is the best method of specifying the accuracy.
It is to be specified in terms of the true value of quantity being measured.
For example, it can be specified as ± 0.1% of true value.
This indicates that in such cases, as readings get smaller, error also gets
152. iii. Accuracy as Percentage of Scale Span:-
For an instrument, if amax is the maximum point for which scale is calibrated,
i.e. full scale reading and amin is the lowest reading on scale.
Then (amax - amin) is called scale span or span of the instrument.
Accuracy of the instrument can be specified as percent of such scale span.
Thus for an instrument having range from 25 units to 225 units, it can be
specified as ± 0.2 % of the span i.e.± [(0.2/l00)x (225 - 25)] which is ± 0.4 units
error in any measurement.
iv. Point Accuracy :
Accuracy is specified at only one particular point of scale.
It does not give any information about the accuracy at any other point on the
scale. Therefore, general accuracy of an instrument cannot be specified, in this
manner. But the general accuracy can be specified by providing a table of the
point accuracy values calculated at various points throughout the entire range of
instrument.
2. PRECISION: It is the measure of consistency or repeatability of
measurement.
Precision means sharply or clearly defined and the readings agree among
themselves. But there is no guarantee that readings are accurate.
153. Example 1 The table shows the set of 5 measurements recorded in a
laboratory.
Calculate the precision of the 3rd measurement
3 Error: The most important static characteristics of an instrument is its
accuracy, which is generally expressed in terms of the error called static
error.
The algebraic difference between the indicated value and the true value
of the quantity to be measured is called an error.
Mathematically it can be expressed as
154. 154
In this expression, the error denoted as e is also called absolute error.
The absolute error does not indicate precisely the accuracy of the
measurement.
For example, absolute error of ±1V is negligible when the voltage to be
measured is of the order of 1000V but the same error of ±1 V becomes
significant when the voltage under measurement is 5V or so. Hence,
generally instead of specifying absolute error, the relative or percentage
error is specified.
155. Example 2: The expected value of the voltage to be measured is 150 V.
However, the measurement gives a value of 149 V. Calculate (i) Absolute error;
(ii) Percentage error; (iii) Relative accuracy; (iv) Percentage accuracy and (v)
Error expressed as percentage of full scale reading, if the scale range is 0-200 V.
156. SENSITIVITY:
Denotes the smallest change in the measured variable to which the
instrument responds. It is defined as the ratio of the changes in the output
of an instrument to a change in the value of the quantity to be measured.
Mathematically it is expressed as,
The sensitivity is always expressed by the manufacturers as the ratio
of the magnitude of quantity being measured to the magnitude of the
response.
Actually, This definition is the reciprocal of the sensitivity is called
inverse sensitivity or deflection factor.
157. Example 3: A particular ammeter requires a change of 2A in its coil to
produce a change in deflection of the pointer by 5mm. Determine its
sensitivity and deflection factor.
Solution : The input is current while output is deflection.
Sensitivity= change in output / change in input = 5 mm /2A . = 2.5 mm / I A
158. Statistical Analysis: Out of the various possible errors, the random
errors can not be determined in the ordinary process of measurements.
Such random errors are treated mathematically.
The mathematical analysis of the various measurements is called
statistical analysis of the data.
For such statistical analysis, the same reading is taken number of times,
generally using different observers, different instruments and by different
ways of measurement.
The statistical analysis helps to determine analytically the uncertainty of
the final test results.
Arithmetic Mean and Median: When the number of readings of the
same measurement are taken, the most likely value from the set of
measured variable values is the arithmetic mean of the number of
readings taken.
The arithmetic mean value can be obtained mathematically as,
159. The approximation with the help of mean value is valid for all data sets if
the measurement errors are distributed equally. about the zero error line.
This means the positive errors are balanced in quantity and magnitude by
the negative errors.
This mean is very close to true value, if number of readings is very large.
But when the number of readings is large, calculation of mean value is
complicated.
In such a case, a median value is obtained which is a close approximation
to the arithmetic mean value.
For a set of measurements xl, x2, x3…….. xn written down in the
ascending order of magnitudes, the median value is given by,
Thus, for a set of eleven measurements xl, x2, ..... xll' the median
value is x(11+l)/2 = x6
For the even number of data values, the median value is midway
between the centre two values.
For twelve measurements xl, ,x2, to xl2 the median value is given by (x6
+x7) /2
160. Deviation from Mean
The deviation tells us about the departure of a given reading from the
arithmetic mean of the data set. This is denoted as d and calculated for
each reading as
160
Key Point: This departure of reading from the arithmetic mean may be
positive or negative.
Average Deviation: The average deviation is defined as the sum of the
absolute values of deviations divided by the number of readings.
This is also called mean deviation.
Standard Deviation:-The amount by /which the n measurement values
are spread about the mean is expressed by a standard deviation. It is also
called root mean square deviation.
The standard deviation is defined as the square root of the sum of the
individual deviations squared, divided by the number of readings.
161. Variance: The variance means mean square deviation, so it is the square of
the standard deviation. It is denoted as V .
in practice for small number of readings less than 20, the denominator in
equation (4a) is expressed as n - 1 rather than n.
162. 1. Problem: Find the mean, median, standard deviation and variance of
the measured data. The following 13 observations are recorded when
measuring a temperature of a same quantity.1089, 1092, 1094, 1095,
1098, 1100, 1104, 1105, 1107, 1108, 1110, 1112, 1115.
Least square fit of experimental data in measurement systems
Where: Yi is the linearized output, yi is the non-linear output.
Substitute a & b values into Y = axi +b, which is then called the least-squares
best fit.
164. SENSITIVITY: Sensitivity is the ratio of change in magnitude of the output
to the change in magnitude of the measured • Sensitivity =
D(output)/D(input)
High Sensitivity is desirable in the Instruments.
Highly sensitive instruments produce less error.
LINEARITY; The maximum deviation of calibration curve from straight line
drawn between no load and full load output.
It is expressed as a percentage of full scale output or as a percentage of
actual reading. % of linearity= (Max. deviation/ Full scale reading) X100
It is highly desirable that the measurement system has a linear
relationship between input and output means that the change in output is
proportional to the change in the value of the measured.
Deviation from true linearity is called linearity error.
The input and output relationship of a linear transducer can be
represented by the following equation: y = mx + c where y is the output
of transducer, x is the input of transducer, m is the slope of curve
(transfer function), c is the offset.
Often, the straight line approach is used for certain range of operation for
165. Problem 1. In an experiment, the following output voltages are obtained
when the displacements are measured by a displacement sensor. Obtain the
best linear relation in accordance with a least square analysis and estimate
(i) output voltage when a displacement of 6.5 mm is measured.
(ii) Sensitivity of the sensor
(iii) % of Non-linearity of the sensor
(iv) Calculate the mean deviation and standard deviation of the Output
Voltage data.
Problem 2. In an experiment, the following output voltages are obtained
when the displacements are measured by a displacement sensor. Obtain the
best linear relation in accordance with a least square analysis and estimate
output voltage when a displacement of 5.5 cm is measured. Calculate the
mean deviation and standard deviation of the Voltage-data.
166. Limiting Errors:
The manufacturers specify the accuracy of the instruments within a certain
percentage of full scale reading.
The components like the resistor, inductor, capacitor are guaranteed to be
within a certain percentage of rated value.
This percentage indicates the deviations from the nominal or specified value
of the particular quantity.
These deviations from the specified value are called Limiting Errors. These
are also called Guarantee Errors.
Example Resistor is specified by the manufacturer as 4.7 k with a
tolerance of ± 5 % then the actual value of the resistance is guaranteed to be
within the limits.
R = 4.7 k ± (5 % of 4.7 k ) = 4.7 k ± 0.235 k = 4.935 k and 4.465
k .
Thus the actual value with the limiting error can be expressed
mathematically a
167. • Relative Limiting Error:
• This is also called fractional
error.
• It is the ratio of the error to the
specified magnitude of a
quantity.
e = relative limiting error
From the above equation, we can
write
• The percentage relative limiting
error is expressed as
The relative limiting error can be
also be expressed as,
168. Combination of Quantities with
Limiting Errors
When the two quantities are
combined, each having limiting
error, then it is necessary to
calculate the overall limiting error.
Let us consider the various
combinations of two quantities and
methods to obtain the
corresponding limiting error.
169. Key Point: The total limiting error is sum of the products obtained by
multiplying the individual limiting error by the ratio of each term to the
resultant function.
171. • Let
The result is same as that obtained
for the product.
If there is product or division of
more than two quantities, then,
If the result is the product of
different powers of two quantities i.e,
172. Example: The r.m.s. current
passing through a resistor of
120±0.5 ohms is 2 ±0.02 A.
Calculate the limiting error in the
value of power dissipation.
el= limiting error while the limiting
error due to resistance is e2.
• As power is the product of I2 and R,
the resultant error is the sum of the
2
• Example: Three resistances have
the following ratings
;R1=15±5%; R2=33 n ± 2 %;
R3 = 75 ± 5 %.
• Determine the magnitude and
limiting error in ohms, if the
resistances are connected in series.
Also obtain percentage relative
limiting error in the resultant.
173. Solution : a) Errors as limiting
errors
Example: Voltmeter reads 111.5V.
The error taken from an error curve is
5.3 %. Find the true value of the
voltage.
Thus, the resultant is 123 with the
limiting error of 5.16 . Thus, δPT=
5.16 and RT=123.Hence the %
relative limiting error is,
Example: In a series circuit of two
resistances, the voltage across R1is
150 ±2V and that across R2 is
75±3V. Determine the percentage
error in the total voltage across the
combination,
a) Considering the errors in two
174. Example: Three resistances are
specified as :R1= 200Ω ±5%, R2=
100Ω±5%, R3=50Ω ±5%.
Determine the magnitude of the
resultant resistance and the
limiting error in percentage and in
ohms if the resistances are
connected in series.
Solution : The resistances are in
series
175. Example Current was measured during
a test as 20.5 A, flowing in a resistor of
0.2Ω . It was found that the ammeter
reading was low by 1.3 % while the
resistance value was high by 0.5 %.
Find the true power as a percentage of
the power that was originally
calculated.
Solution: The ammeter reading is
20.5A
But true reading is higher by 1.3 % as
ammeter is showing low reading.
Example : A particular bridge gives
the value of the unknown resistance
as,
176. Basic D.C. Ammeter
The basic D.C ammeter is
galvanometer.
The coil winding of a basic
movement is very small and light
and hence it can carry very small
currents.
For large currents, the major part
of current is required to be
bypassed using a resistance called
shunt. It is shown in the Fig.
below.
Let
Fig. Basic d.c, ammeter
177. As the two resistances Rsh and Rm
are in parallel, the voltage drop
across them is same.
The m is called multiplying power
of the shunt and defined as the ratio
of total current to the current
through the coil. It can be expressed
as,
Example 1: A 2mA meter with an
internal resistance of 100Ω is to be
converted to 0-150 mA ammeter.
Calculate the value of the shunt
resistance required.
Solution: Given values are,
.
178. Example 2. A moving coil
ammeter has fixed shunt of 0.01Ω.
With a coil resistance of 750 Ω and
a voltage drop of 400 mV across it,
the full scale deflection is
obtained.
a) Calculate the current through
shunt.
b) Calculate the resistance of meter
to give full scale deflection if
the shunted current is 50 A.
Solution:(a) The drop across the
shunt is same as drop across the
coil.
b) The voltage across shunt for
shunted current of 50 A is,
For this voltage the meter
should give full scale deflection.
In first case, the current through
meter for full scale deflection
was,
The same 1m must flow for new
voltage across the meter of 0.5
V.
This is the resistance of the
meter required for 50 A shunted
current to give full scale
deflection.
179. Basic D.C. Voltmeter :The basic d.c. voltmeter is galvanometer. The
resistance is required to be connected in series with the basic meter to use it
as a voltmeter.
This series resistance is called a multiplier. The main function of the
multiplier is to limit the current through the basic meter so that the meter
current does not exceed the full scale deflection value.
The voltmeter measures the voltage across the two points of a circuit or a
voltage across a circuit component. The voltmeter must be connected across
the two points or a component, to measure the potential difference, with the
proper polarity. The multiplier resistance can be calculated as :
Rm = Internal resistance of coil i.e. meter
Rs = Series multiplier resistance
Im =Full scale deflection current
V = Full range voltage to be measured
Example :A moving coil instrument gives a full scale deflection for a
current of 20mA with a potential difference of 200mV across it. Calculate :
i) Shunt required to use it as an ammeter to get a range of 0- 200 A.
ii) ii) Multiplier required to use it as a voltmeter of range 0- 500V.
180. Multi range Voltmeters
The range of the basic d.c. voltmeter can be extended by using number of
multipliers and a selector switch. Such a meter is called multi range
voltmeter
The R1, R2, R 3 and R4 are the four
series multipliers. When connected in
series with
the meter, they can give four different
voltage ranges as V1,V2, V3 and V4. The
selector
switch S is multi position switch by
181. The mathematical analysis of basic d.c. voltmeter is equally applicable for
such multi range voltmeter.
Practical Multirange Voltmeter
More practical arrangement of multiplier resistances In this arrangement, the
multipliers are connected in a series string.
The connections are brought out from the junctions of the resistances. The
selector switch is used to select the required voltage range.
When the switch S is at position VI' RI + R2 + R 3 + R4 acts as a multiplier
resistance. While when the switch S is at position V4 then the resistance R4
only acts as multiplier resistance. The V4 is the lowest voltage range while
VI is the maximum voltage range. The multiplier resistances can be
calculated as :
In position V4 , the multiplier is R4 only.
The total resistance of the circuit is say RT.
182. Example : A basic galvanometer.
movement with an internal resistance of
50 Q and a full scale deflection current
of 2mA is to be used as a multi range
voltmeter. Design the series string of
multipliers to obtain the voltage ranges
of 0 - 10 V, 0 - 50 V, 0 - 100 V, 0- 500 V
186. What is PLC?
A PLC is a solid state / industrial computer that performs
discrete or sequential logic in a factory environment.
It was originally developed to replace mechanical relays,
timers, counters.
A sequence of instructions is programmed by the user to the
PLC memory. Its purpose is to monitor crucial process
parameters and adjust process operations accordingly.
2 September 2023
Introduction
187. History and Origin
Developed to replace relays in the late 1960s
PLC began in the 1970s, and has become the most common
choice for manufacturing controls.
The PLC was invented in response to the needs of the American
automotive manufacturing industry (primarily General motors).
Costs dropped and became popular by 1980s
Now used in many industrial designs
2 September 2023
188. Programmable Logic Devices (PLD)
Programmable Logic Devices (PLD) - to perform different
control functions, according to the programs written in its
memory, using low level languages of commands.
Microprocessor, a digital integrated circuit –digital functions
necessary to process information
Microcomputer - uses microprocessor as its central
processing unit and contains all functions of a computer
Programmable Logic Controller (PLC) - to control the
operation of electro-mechanical devices
2 September 2023
189. Contd…
What is a Microprocessor (MP)?
The word Microprocessor is a combination of two words micro and
processor
In our context processor means a device which processes binary
numbers (0’s and 1’s)
Micro means small
Before the birth of microchip, processors were large discrete
elements
After invention of microchip, the size of the processor became
much smaller
A microprocessor is a multi-purpose, programmable, integrated
logic device that reads binary instructions from a storage device
called memory, accepts binary data as input and processes the data
according to those instructions and provides result as an output.
2 September 2023
190. Contd…
Differences between microcomputer, microprocessor and
microcontroller
Microcomputer– a computer with a microprocessor as its CPU.
Includes memory, I/O
Microprocessor– silicon chip which includes ALU, register circuits
and control circuits
Microcontroller– silicon chip which includes microprocessor,
memory and I/O in a single package.
2 September 2023
191. Organization of Microcomputers
Microcomputer – a computer with a microchip(microprocessor) as
its CPU.
It Includes memory and I/O
It combines three basic components
Microprocessor, memory and I/O
Block diagram of Micro-computers
2 September 2023
193. Contd…
A typical programmable machine has basic three components :
1. Processor,
2. Memory
3. I/O (input/output) :Hardware
A set of instructions written for the processor to perform a task is
called program
A group of programs is called software.
2 September 2023
194. Microprocessor
a multi-purpose, programmable device
Reads binary instructions from a storage device called
memory
Processes data according to the instructions
Provides results as output
2 September 2023
195. Contd…
Microprocessor applications are in two classified primarily
categories :
Reprogrammable Systems : Micro computers
Embedded Systems : photocopying machine, Digital camera
Operates in binary digits 0 and 1, bits.
Electrical voltages in the machine, generally 0 - low
Voltage level and 1 level, - high voltage level
A group of bits, word
Word length of 8 bits - byte
Word length of 4 bits - Nibble
A command in binary to accomplish a task- instructions.
Instructions
entered through input devices
can be stored in a storage device called memory
2 September 2023
197. Contd…
Microprocessor based programmable controllers
A controller or microprocessor-based controller can be
subdivided into two categories :
1. Programmable Logic Controllers
2. Microcontroller
2 September 2023
198. Contd…
Micro controller
A microprocessor-based system
Implements the functions of a computer and a controller on a
single chip
Typically programmed for one application
Dedicated to a specific control function
Automobiles, aircraft, medical electronics and home
appliances
It is small and can be embedded in an electromechanical
system without taking up much space
Functions are completely designed into the chip.
Very little user programmable memory
Motorola 68HC11, Zilog Z8 and Intel MCS51 and 96 series.
2 September 2023
200. Contd…
special form of
microprocessor-based controller that uses a programmable
memory to store instructions and to implement functions such as
logic, sequencing, timing, counting and arithmetic in order to
control machine and process.
The main advantage of PLC is that:
It is flexible
Cost effective
Can be used for any control system complexity
Easer to troubleshoot
Programmable Logic Controller
A programmable logic controller is a
2 September 2023
201. Contd…
Advantages
PLC Saves
Material cost
Installation cost
Troubleshooting
Labor cost
By Reduced wiring & associated
errors
Less space
No moving parts - rugged
Possibility of reprogramming
Value added benefits
Reliability
Flexibility
Advanced Function
Communication
Speed
Diagnostics
2 September 2023
202. Contd…
Disadvantages
Too much work required in connecting wires.
Difficulty with changes or replacements.
Difficulty in finding errors; requiring skillful work force.
2 September 2023
203. Contd…
Basic Components of a PLC System
Network Interface
Most PLCs have the ability to communicate with other devices.
The PLC will communicate to the other devices through a
network interface.
Various Brands in PLC
Allen Bradley
Siemens
Modicon
Mitshubishi
GE Fanuc
Omron
USA
Germany
France
Japan
USA
Japan
2 September 2023
204. Contd…
PLC’s Come in a Variety of Sizes...
Pico
Typically less than 20 I/O
Micro
Typically less than 32 I/O
Small
Typically less than 128 I/O
Medium
Typically less than 1024 I/O
Large
Typically greater than 1024 I/O
2 September 2023
205. Contd…
Variety of Shapes/Configurations
Packaged
MicroLogix 1000,1200 and 1500
Packaged with expansion
MicroLogix 1200 and 1500
Modular (rack less)
MicroLogix 1200 and 1500
Modular (rack based)
SLC 500 and PLC5
Distributed
SLC 500 and PLC5
2 September 2023
206. Contd…
Packaged PLC
Power supply, inputs, outputs and communication port are
enclosed in a single package. Input and output devices are wired
individually to the packaged controller.
Packaged PLC With Expansion
Base is identical to the standard Packaged PLC, but it also has the
ability to drive additional I/O. The most common form of
expansion is a block of I/O that uses the same base, or makes use
of different types of expansion “modules”.
2 September 2023
207. Contd…
Modular PLC’s
Mix N Match Components
Processors, Power Supplies and I/O are plugged into a rack
or chassis
Available in Small, Medium, and Large platforms
Flexibility results in higher costs when compared to
packaged
Modular Rack-Less PLC’s
Identical in functionality to rack based PLC’s
Typically not as robust (packaging)
Typically found on “smaller” (small and medium) sized PLC’s. Will
likely become the prevalent form of packaging in the future
2 September 2023
208. Contd…
One of the benefits of a PLC system is the ability to locate the I/O
modules near the field devices to minimize the amount of wiring
required.
PLC Hardware System
A PLC system has five basic components
The processor unit
Memory
The power supply unit
Input / output interface
Programming device
PLCArchitecture
The Structure of PLC is based on the same principles as those
employed in computer architecture.
2 September 2023
209. Input –output devices
Input devices are connected to the terminal strip under the bottom
cover of the PLC.
Electrical contacts, pushbuttons and switches as input devices
2 September 2023
210. Input –output devices
Output devices, such relays and light, are connected to the
terminal strip under the top cover of the PLC.
Actuators, relays, indicator lamps, solenoids etc are out put
devices
2 September 2023
213. Contd…
Actuators and Switches
The device, which changes the state of a contact is called an
actuator
The combination of an actuator and one or more contacts is
called a switch
Push button switch
A key selector
Foot switches
Roller lever switches and plunger operated switches : limit
switches
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216. Bit Logic
Bit Logic
POSITIVE & NEGATIVE Transition
The Positive Transition (EU) contact allows power to flow for
one scan for each off-to-on transition.
The Negative Transition (ED) contact allows power to flow for
one scan for each on-to-off transition.
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217. Contd…
Bit Logic
SET & RESET
The Set (S) and Reset (R) instructions set (turn on) or reset (turn
off) the specified number of points (N), starting at the specified
address (Bit). You can set or reset from 1 to 255 points.
If the Reset instruction specifies either a timer bit (T) or counter
bit (C), the instruction resets the timer or counter bit and clears
the current value of the timer or counter.
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218. Timers
Timers are devices that count increments of time. They are used
with traffic lights, for example, to control the length of time
between signal changes.
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