Industrial Automation: PLC and SCADA
Course Code: 116h58C401
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What is Automation?
Automation Technology concerned with application of mechanical, electrical, electronic and
computer based system to operate and control production
• Use or introduction of automatic equipment in a manufacturing or other process
• This includes:
• Automatic machine tools to operate or process the parts
• Automatic assembly of machines
• Industrial robots
• Automatic material handling and storage systems
• Automatic inspection for quality control
• Feedback control and computer process control
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Benefits of automation
• Increased productivity
• Reduced the labor shortage
• Safety
• Improved product quality
• Good customer service
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Before programmable controllers..?
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Introduction to Programmable Logic Controller
• It is an industrial graded computer that is capable of being programmed to perform control
functions
• A PLC is an example of a real time system since the output of the system controlled by the
PLC depend on the input conditions
• PLC is capable not only performing relay switching tasks but also performing other
applications like timing, counting, calculating, comparing and processing of analog signals
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Definition of PLC
•
PLC is digitally operated/controlled electronic system, designed for use in industrial process
which uses programable memory for the internal storage of user defined instructions for
implementing specific functions like logic sequencing, timing, counting and arithmetic to
control the digital and analog inputs and outputs in a process.
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Advantages of using PLC
• Increased Reliability
• More flexibility
• Lower cost
• Communication capability
• Faster response
• Easier to troubleshoot
• Easier to test field devices
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Block Diagram of PLC
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Different types of PLC
Fixed/Integrated/Compact PLC
•
The processor and I/O are packaged together, and the I/O terminals will have a fixed number
of connections built in for inputs and outputs
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Different types of PLC
Modular PLC
• It is divided by different compartments into which separate modules can be plugged
• The basic modular controller consist of a rack, power supply, processor module (CPU), I/O
modules and an operator interface for programming and monitoring
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Types of PLC according to output
Relay Output
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Transistor Output
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Types of PLC according to the size
• Mini PLC : usually have 128 to 512 I/O points
• Micro PLC: have 15 to 128 I/O points. They are most commonly used in very small
automation or control systems like amusement rides
• Nano PLC: have less than 15 I/O points. Usually, they are seen in PLC trainer
systems
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PLC Hardware components
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The I/O section
• All field devices are connected to this section and provide the interface between them and
the CPU
• The processor receives the signal from the remote Input modules and sends signals back to
their Output modules via the communication module
• Memory system stores the information about the status of all the inputs and outputs
• An address is a label or number that indicates where a certain piece of information is located
in a PLC’s memory
• Module’s job is:
- verify the input signal from field device
- Isolate the high voltage field device signal from the low voltage CPU signal
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Types of Input/Output Module
Discrete I/O Module
• It connects field input devices of the ON/OFF nature such as selector switch, push buttons and
limit switches.
• Output control is limited to devices such as lights, relays, solenoids and motor starters that
requires simple ON/OFF switching
• Discrete I/O covers bit oriented inputs and outputs
• Each bit represents a complete information element in itself and provides the status of some
external contacts
• I/O modules are available in different AC and DC voltage ratings
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Discrete input module
• Block diagram of a AC discrete input module
• It sense when a signal is received from a field device
• Convert the input signal to the correct voltage level for the particular PLC
• Isolate the PLC from fluctuations in the input signal’s voltage or current
• Send a signal to the processor indicating which sensor originates the signal
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Discrete output module
• Block diagram of a AC discrete output module
• TRIAC outputs can be used only for the control of AC devices
• Transistor outputs can be used only for the control of DC devices
• Relay outputs can be used for the control of both AC and DC devices
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Types of Input/Output Module
Analog I/O Module
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Analog Input Module
• This module contains the circuit necessary to accept an analog voltage or current signal from
the field devices
• The transition of analog signal to digital value is accomplished by an Analog to Digital
converter
• Analog input modules are available in two types: Unipolar and Bipolar
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Analog Output Module
• It receives digital data from the processor which are converted into a proportional voltage or
current to control an analog field device
• This is done by using Digital to Analog converter
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Central Processing Unit (CPU)
• Two sections in Processor module : CPU section and memory section
• CPU section executes the program and makes the decisions needed by the PLC to operate
• Memory section electronically stores the PLC program
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PLC scan cycle
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Memory design
• Memory is the element that store information, programs and data in a PLC
• The user memory of PLC includes space for the user program as well as the addressable
memory locations for storage of data
• Data are stored in memory locations by a process called writing
• Data are retrieved from memory by what is referred to as reading
• Memory locations refers to an address in the CPU’s memory where a memory word can be
stored
• One location per coil or contact
• Sections of memory used to store the status of inputs and outputs are called input status files
or tables and output status files or tables
• These term simply refer to a location where the status of an input or output device is stored
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Programming terminal devices
• To enter, modify and troubleshoot the PLC program
• The simplest type of programming device is the hand held type programmer
• Another type is to use a PC in conjunction with the manufacturer's programming software
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Sinking and Sourcing
• Detecting input field device conditions
• construct a closed circuit containing the input device, the PLC input module, and a 24V DC
power supply
• If the switch is open, there is 0V at the module input terminal. If the switch is closed, there is
+24V at the module input terminal.
• These voltage or no-voltage conditions are represented by 1’s and 0’s in the PLC memory.
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Sinking and Sourcing
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Sinking and Sourcing
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Sinking and Sourcing
1) Sinking PLC digital input modules
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2) Sourcing PLC digital input modules
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Sinking and Sourcing
Active Input Field Devices
1) If the input device is a sourcing type, the PLC input module must be a sinking type.
2) If the input device is a sinking type, the PLC input module must be a sourcing type.
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Sinking and Sourcing
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Sinking and Sourcing
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How Processor Works?
START UP MODE
RUN MODE
Process Image Input Memory ‘I’ is
Cleared
‘Q’ Memory is written to Physical
Output
Outputs are initialized with last
value
State of Physical Input is written to
‘I’ Memory
Any start up-logic is executed
Logic is executed
State of the physical Input is
copied to ‘I’ Memory
Self-test diagnostic is performed
Any interrupts presents are queued
to execute
Any interrupts presents are queued
to execute
Writing of
Process Memory ‘Q’ to Physical
O/P is enabled
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Interrupts and communications are
processed during any part of cycle
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Modes of operation
Program Mode:
• This mode is used to enter a new program, edit or update an existing program, upload files,
download files or change any software configuration file in the program
• All outputs from the PLC are forced off
RUN Mode:
• This is to execute the user program
• Input devices are monitored and output devices are
energized accordingly
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Modes of operation
Test Mode:
• This mode is used to operate or monitor the user program without energizing any outputs
• The processor still reads inputs, execute the program and updates the output status table files
but without energizing the output circuits
• Variation of test mode can include single step test mode, single scan test mode etc.
Remote Mode:
• This mode allows the PLC to be remotely changed between program and run mode by a
personal computer connected to the PLC processor
• This mode is beneficial when the controller is in a location that is not easily accessible
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Operation mode of CPU
The CPU has three modes of operation: STOP mode, STARTUP mode, and RUN mode. Status LEDs
on the front of the CPU indicate the current mode of operation
In RUN mode, the scan cycle is
executed repeatedly. Interrupt events
can occur and be processed at any time
within the program cycle phase
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In STOP mode, the CPU is not executing
the program, and you can download the
project.
You can download the project only when
the CPU is in STOP mode.
In STARTUP mode, the
CPU executes any
startup logic (if present).
Interrupt events are not
processed during the
startup mode.
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Memory area in S7-1200
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Memory Area
Description
I-Process Image
Input
The CPU copies the state of physical inputs to I memory at the beginning
of the scan cycle.
Q-Process Image
Output
The CPU copies the state of Q memory to the physical outputs at the
beginning of the scan cycle
M
Bit Memory
The user program reads and writes the data stored in M Memory. Any
code block can access the M memory. You can configure addresses
within M memory to retain the values of the data after a power cycle
L
“Temp” memory
Whenever a code block is called, the CPU allocates the temporary, or
local memory (L) to be used during the execution of the block. When the
execution of the code block finishes, the CPU reallocates the local
memory for the execution of other code blocks.
DB
Data Block
Use the DB memory for storing various types of data, including
intermediates status of an operation or other control information
parameters for FBs, and data
Structures required for many instructions such as timers and counters.
You can specify data block to be either read/write or read only. You40can
access data block memory in bits, bytes, words, or double words
Programming Methods of PLC
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Programming Methods of PLC
Rules for PLC Ladder Diagram Programming
➢ 1. Inputs can be used in Series as well as Parallel to form a connection
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Programming Methods of PLC
➢
2. Outputs (or coil) can be used only in Parallel
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Programming Methods of PLC
➢
3. One Input can be used in multiple times in one program
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Programming Methods of PLC
➢
4. One Output cannot be used multiple times in one
program, except in Set/Reset and Latch/ Unlatch functions
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Programming Methods of PLC
➢ 5. Input Address cannot be used as an Output Address
➢ 6. Outputs Address can be used as Inputs Address
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Case 1: Converting Schematic to Ladder Logic
Schematic Diagram
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Ladder Diagram
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Case 1: Converting Schematic to Ladder Logic
Schematic Diagram
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Ladder Diagram
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Basic Electrical Circuits- Fundamentals
Schematic Diagram
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Ladder Diagram
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Basic Electrical Circuits- Fundamentals
Schematic Diagram
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Ladder Diagram
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Bit Logic Instructions in LAB- NO, NC, OUT
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Ladder Diagram: Logic Gates
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Ladder Diagram: Logic Gates
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Ladder Diagram: Logic Gates
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Data Storage in PLC
The smallest unit of information in a digital system is known as a “bit”. A bit stores one of
the two possible states, either a “0” (False or not True) or “1” (True).
A light switch is an example of a “binary” system with only two states. The light switch
determines either a “light on” or a “light off” state, and this value can be stored in one bit. If the
light switch is on (“true”), then the value is 1. if the light is switched off (“off”), then the value is 0.
1 WORD = 16 BITS = 2 BYTE
1 BYTE = 8 BITS
BIT
𝟐𝟏𝟓
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𝟐𝟏𝟒
𝟐𝟏𝟑
𝟐𝟏𝟐
𝟐𝟏𝟏
𝟐𝟏𝟎
𝟐𝟗
𝟐𝟖
𝟐𝟕
𝟐𝟔
𝟐𝟓
𝟐𝟒
𝟐𝟑
𝟐𝟐
𝟐𝟏
𝟐𝟎
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Data Type Supported by S7-1200
Few are some of the widely used data type supported in S7-1200.
Data Type
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Size
Range
Bool
Byte
1 bit
8 bits
0~1
00 h ~ FF h
Word
DWord
Char
16 bits
32 bits
8 BITS
0000 h ~ FFFF h
00000000 h ~ FFFFFFFF h
00 h ~FF h
Int
Dint
16 bits
32 bits
-31768 ~ 32767
-2,147,483,648 ~ 2,147,483,647
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Pulse Timer (TP)
TIMER OERATIONS
• Generate pulse instruction to set the output Q for a programmed duration.
• The instruction is started when the result of the input IN changes from 0 to 1 (positive
edge).
• Programmed time (PT) begins when the instruction starts. In this timer even if a new
positive edge is detected, the signal state at the output Q is not affected as long as the
PT time duration is running.
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Pulse Timer (TP)
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ON-Delay Timer (TON)
•
•
TIMER OERATIONS
ON delay timer instruction to delay setting of the Q output by the programmed duration PT. The
instruction is started when the result of the input IN changes from 0 to 1 (positive edge).
The timer value starts at T#0s and ends when the value of duration PT is reached. The ET output is
reset as soon as the signal state at the IN input changes to 0.
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TIMER OERATIONS
ON-Delay Timer (TON)
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TIMER OERATIONS
OFF - Delay Timer (TOF)
•
Off delay timer instruction to delay resetting of the Q output by the programmed duration
PT.
•
The Q output is set when the result of logic operation (RLO) at input IN changes from 0 to
1 (positive signal edge).
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TIMER OERATIONS
OFF - Delay Timer (TOF)
•
•
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Changing PT has no effect while the timer runs
Changing IN to TRUE, while the timer runs, reset
and initialize the timer
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TIMER OERATIONS
• RETENTIVE ON Delay (TONR)
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TIMER OERATIONS
• RETENTIVE ON Delay (TONR)
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COUNTER OPERATION
Count Up
• The “Count Up” counter (CTU) counts up by 1 when the value of the parameter
CU changes from 0 to 1.
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COUNTER OPERATION
Count Down
• The “Count Down” counter (CTD) counts down by 1 when the value of the input
parameter CD changes from 0 to 1.
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COUNTER OPERATION
Count Up and Down (CTUD)
• The “count up and down” counter (CTUD) counts up or down by 1 on the 0 to 1
transition of the count up (CU) or count down(CD) inputs.
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Various Data Types
Data Types
• The data type defines the properties of the data, for example, the representation of
the contents and the valid memory areas
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SET & RESET Operation
SET Instruction
• When S (SET) is activated, then the data value at the OUT address is set to 1.
When S is not activated, OUT is not changed.
RESET Instruction
• When R (Reset) is activated, then the data value at the OUT address is set to 0.
When R is not activated, OUT is not changed.
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Example:
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SET & RESET Operation
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SET & RESET Operation
Exercise:
Write a logic to latch two outputs Q0.0 and Q0.1 with I0.0 and unlatch using I0.1
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SET & RESET (Field)
SET Instruction
• when SET_BF is activated, a data value of 1 is assigned to “n” bits starting at
address tag OUT. When SET_BF is not activated, OUT is not changed.
RESET Instruction
• RESET_BF writes a data value of 0 to “n” bits starting at address tag OUT. When
RESET_BF is not activated, OUT is not changed.
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SET & RESET (Field)
Example:
Write a logic to latch three outputs Q0.0-Q0.2 with I0.0 and unlatch all
using I0.1
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SET Dominant & RESET Dominant
SET/Reset Flip Flop (SR)
• SR is a Reset dominant latch where the reset dominates. If the set (S)
and reset (R1) signals are both true, the value at address Q0.0 will be 0.
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SET Dominant & RESET Dominant
Reset/SET Flip Flop (RS)
• RS is a dominant latch where the set dominates. If the set (S1) and
Reset (R ) are both true, the value at address Q0.0 will be 1.
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SET Dominant & RESET Dominant
Example
Write a logic to latch the motor Q0.0 with I0.0 (PB) and include two
emergency switches I0.2 and I0.3 to unlatch it. Which flip flop you will
use?
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Positive and Negative Edge
Positive Edge- SCAN Operand
• The state of this contact is TRUE when a positive transition (OFF to ON) is
detected on the assigned bit I0.0.
• The bit M0.0 will be ON for one clock cycle.
Negative Edge- SCAN Operand
• The state of this contact is TRUE when a negative transition (ON to OFF) is
detected on the assigned bit I0.1.
• The bit M0.1 will be ON for one clock cycle.
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Positive and Negative Edge
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Positive and Negative Edge
• Example:
• Write a logic to latch the motor when I0.0 goes from OFF to ON and unlatch the
motor when I0.1 goes from ON to OFF.
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P_TRIG and N_TRIG
P_TRIG-SCAN RLO
• The Q output power flow or logic state is TRUE when a positive transition (OFF to
ON) is detected on the CLK power flow.
N_TRIG – SCAN RLO
• The Q output power flow or logic state is TRUE when a negative transition (ON to
OFF) is detected on the CLK power flow.
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P_TRIG and N_TRIG
Write a logic to latch the motor when either I0.0 or I0.1 goes from OFF to ON and
unlatch the motor when either I0.2 or I0.3 goes from ON to OFF
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Comparator Operations
The Compare Instructions perform a Comparison of two values with the same data
type.
•
•
•
•
•
•
•
•
Equal (==)
Not Equal (<>)
Greater or Equal (>=)
Less or Equal (<=)
Greater than (>)
Less than (<)
IN_Range – Value within Range
OUT_Range – Value outside Range
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Example- Comparator Operations
Take an example of Counter with PV 10 and utilize all the comparison operators
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Math Operations
ADDITION- For addition of two or more inputs
SUBTRACT- for subtraction of two inputs
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Math Operations
MULTIPLICATION- for multiplication of two or more inputs
DIVISION- for division of two inputs
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Math Operations
• MOD- return remainder of division
• CALCULATE- to calculate the pre-defined equation
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Math Operations
• INC- used to increment data by +1
• DEC- used to decrement data by 1
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Math Operations
• GET MINIMUM- Compare the value at the input and write the lowest value to the
output
• GET MAXIMUM- Compare the value at the input and write the highest value to
the output
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Math Operations
• SET LIMIT- limit the value at the input to the values at MN and MX input
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Math Operations
• SET LIMIT- limit the value at the input to the values at MN and MX input
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Program Control Operations
• JUMP & LABEL
• JUMP LIST
• SWITCH: Jump Distributor
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JUMP & LABEL
• If the result of logic operation
(RLO) at the input of the
instruction is “1”, the jump to the
network identified by the specified
jump label is executed
• If the condition at the input of the
instruction
is
not
fulfilled
(RLO=0), execution of the program
continues in the next network.
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JUMP_LIST
• Jump List Operation
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JUMP_LIST
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SWITCH: Jump Distributor
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Word Logic Operations
•
•
•
•
•
•
•
•
•
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AND
OR
XOR
INV
DECODE
ENCODE
SELECT
MUX
DEMUX
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AND Operation
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AND Operation
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OR Operation
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OR Operation
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XOR Operation
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XOR Operation
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INV Operation
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INV Operation
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DECODE Operation
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DECODE Operation
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ENCODE Operation
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ENCODE Operation
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SELECT Operation
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MUX Operation
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DEMUX Operation
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Interfacing of PLC with I/Os
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SWITCH
• Push Buttons - 1) momentary Push Button 2) Maintained Push Button
• Selector Switch
• Limit Switches
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SWITCH
• Push Buttons - 1) momentary Push Button 2) Maintained Push Button
• Selector Switch
• Limit Switches
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SENSORS
• Inductive Proximity Sensors
• Capacitive Proximity Sensors
• Photo Electric Proximity Sensors
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How Proximity Sensor Works?
• A proximity sensor is a sensor which detects the presence of nearby objects without
any physical contact
• This can be done using the electromagnetic field or electromagnetic radiation beam
in which the field or return signal changes in the event of the presence of any object
in its surrounding. This object sensed by the proximity sensor is termed as a target.
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Features of the Proximity Sensor
1. Contactless Sensing
2. Unaffected by Surface Condition
3. Suitability for a Wide Range of Applications
4. Longer Service Life
5. High-Speed Response
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Capacitive Sensor
• Capacitive proximity sensors are non-contact devices that can detect the presence or
absence of virtually any object regardless of material
• They utilize the electrical property of capacitance and the change of capacitance based
on a change in the electrical field around the active face of the sensor
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Capacitive Sensor
Principle of operation
• A capacitive sensor acts like a simple capacitor
• A metal plate in the sensing face of the sensor is electrically connected to an internal
oscillator circuit and the target to be sensed acts as the second plate of the capacitor
• Unlike an inductive sensor that produces an electromagnetic field a capacitive sensor
produces an electrostatic field
• The external capacitance between the target and the internal sensor plate forms a part
of the feedback capacitance in the oscillator circuit
• As the target approaches the sensors face the oscillations increase until they reach a
threshold level and activate the output
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Capacitive Sensor
Principle of operation
• The capacitive proximity sensor consist a high-frequency oscillator along with a
sensing surface formed by two metal electrodes. When an object comes near the
sensing surface, it enters the electrostatic field of the electrodes and changes the
capacitance of the oscillator.
• the oscillator circuit starts oscillating and changes the output state of the sensor when it
reaches certain amplitude. As the object moves away from the sensor, the oscillator’s
amplitude decreases, switching the sensor back to its initial state
• The capacitive proximity sensor detects the larger dielectric constant of a target easily
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Capacitive Sensor
• Capacitive sensors have the ability to adjust the sensitivity or the threshold level of the
oscillator
• The sensitivity adjustment can be made by adjusting a potentiometer, using an integral
teach pushbutton
• If the sensor does not have an adjustment method then the sensor must physically be
moved for sensing the target correctly
• Increasing the sensitivity causes a greater operating distance to the target
• Large increases in sensitivity can cause the sensor to be influenced by temperature,
humidity, and dirt.
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Sensor connection
The colors of these wires are brown, blue, black, and white
1) The brown wire gets connected to twenty-four volts DC positive
2) The blue wire gets connected to twenty-four volts DC negative
3) The black and white wires are the sensor output wires. The black wire is the sensor’s
normally open output wire. The sensor will send out a signal on the black wire when it
detects the target. The sensor stops sending this signal when it does not detect a target.
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Sensor connection
• 4) The white wire is the sensor’s normally closed output wire. The sensor will send
out a signal on the white wire when it does not detect a target. The sensor stops
sending this signal when the target is detected.
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Capacitive sensor’s outputs
• A capacitive sensor’s outputs can be a positive signal (or PNP) or a negative signal
(or NPN). Depending on how the sensor outputs will be connected will determine
what style of sensor outputs are needed.
•
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Inductive Proximity Sensor
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•
•
•
•
Inductive Proximity Sensor
The sensor itself contains an oscillator circuit and a coil from which an
electromagnetic field radiates out and induces eddy currents in any nearby metallic
objects
Detector circuit and output circuit
The eddy currents have the effect of attenuating the oscillations from the amplifier.
This reduction in oscillations is registered as the presence of a metallic object.
Because only metallic objects have inductive properties, inductive sensors cannot be
used to detect plastic or cardboard or other non-metallic objects
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Inductive Proximity Sensor
Working Principle
• The oscillator creates a symmetrical, oscillating magnetic field that radiates from the
ferrite core and coil array at the sensing face
• When a ferrous target enters this magnetic field, small independent electrical currents
(eddy currents) which are induced on the metal’s surface.
• Because of magnetic field limitations, inductive sensors have a relatively narrow
sensing range like from fractions of millimeters to 60 mm on an average
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Inductive Proximity Sensor
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Housing Designs
➢ Cylindrical
• M3, M4 , M4.5….M8….M12….M18…M30
➢ Surface / Rectangular
➢
•
➢
•
Slot
2-30mm slot width
Ring
10-100 mm Ring diameter
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Inductive Proximity Sensor
Electrical Connections
AC Sensors
• 20-250V AC
• 2 or 3 wires
• NO/NC
• Programmable NO/NC
DC Sensors
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8 or 10-30 or 10-60 VDC
2,3 or 4 wires
Open/closed
Current sourcing (PNP)
Current Sinking (NPN)
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Applications:
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Photoelectric Proximity Sensor
• They are able to detect both metallic and non-metallic targets
• The main components of this sensor are :
• Emitter, Detector and associated electronics
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Photoelectric Proximity Sensor
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Working Principle of Photoelectric Sensor
There are three main sensing methods:
• Through beam method
• Retro-reflective method
• Diffuse or Reflective method
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Working Principle of Photoelectric Sensor
Through beam method
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Working Principle of Photoelectric Sensor
Retro-reflective method
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Working Principle of Photoelectric Sensor
Diffuse or Reflective method
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Applications
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Resistance temperature detector (RTD)
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Resistance temperature detector
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Also known as a Resistance Thermometer or RTD
Electronic device used to determine the temperature by measuring the resistance of an
electrical wire
This wire is referred to as a temperature sensor
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Resistance temperature detector
The variation of resistance of the metal with the variation of the temperature is given as,
Rt and R0 are the resistance values at toC and 0oC temperatures. α and β are the constants
depends on the metals
For small range of temperature
In RTD devices; Copper, Nickel and Platinum are widely used metals
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Resistance temperature detector
• Copper, Nickel and Platinum are having different resistance variations with respective
to the temperature variations
• That is called resistance-temperature characteristics
• Platinum has the temperature range of 650oC, and then the Copper and Nickel have
120oC and 300oC respectively
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Construction of Resistance Temperature Detector or RTD
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The wire is wound on a form (in a coil) on notched mica cross frame to achieve small
size, improving the thermal conductivity, to decrease the response time and a high rate
of heat transfer
In the industrial RTD’s, the coil is protected by a stainless steel sheath or a protective
tube
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Construction of RTD
• Mica is placed in between the steel sheath and resistance wire for better electrical
insulation
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Signal Conditioning of RTD
• the RTD value is measured by using a bridge circuit
• By supplying the constant electric current to the bridge circuit and measuring
the resulting voltage drop across the resistor, the RTD resistance can be
calculated
• The temperature is determined by converting the RTD resistance value using
a calibration expression
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Thermistor
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Thermistor
• Type of resistor whose electrical resistance varies with changes in temperature
• Thermistors act as a passive component in a circuit
• Thermistor principle is its dependency on-resistance values on the change in
temperature
• The value of resistance can be measured by using an ohmmeter
• The change in the resistance is depending upon the material chosen in the
construction of the thermistor
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Thermistor
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The exact relationship between how the changes in the temperature will affect the
resistance of the thermistor – then by measuring the thermistor’s resistance we can
derive its temperature
The resistance changes depends on the type of material used in the thermistor
The relationship between a thermistor’s temperature and resistance is non-linear
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Thermistor Types
There are two types of thermistors:
1. Negative Temperature Coefficient (NTC) Thermistor
2. Positive Temperature Coefficient (PTC) Thermistor
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NTC Thermistor
When the temperature increases, resistance decreases and when temperature
decreases, resistance increases
Temperature and resistance are inversely proportional
These are the most common type of themistor
The relationship between resistance and temperature in an NTC thermistor is
governed by the following expression:
RT -- is the resistance at temperature T (K)
R0 -- is the resistance at temperature T0 (K)
T0 --is the reference temperature (normally 25oC)
β --nominal value is taken as 4000
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NTC Thermistor
• A higher value of β means a higher variation in resistance for the same rise in
temperature –the sensitivity (and hence accuracy) increases
• thermistors is a non-linear sensor
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PTC Thermistor
• When temperature increases, the resistance increases and when temperature decreases,
resistance decreases
• they are frequently used as a form of circuit protection
• PTC thermistors can act as current-limiting device
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Digital thermometers (thermostats)
Automotive applications (to measure oil and coolant temperatures in cars & trucks)
Household appliances (like microwaves, fridges, and ovens)
Rechargeable batteries (ensure the correct battery temperature is maintained)
To measure the thermal conductivity of electrical materials
Used in Wheatstone bridge circuits
To protect the circuits from the overloading effect that is by increasing the resistance
value. Hence the thermistors are considered as the circuit protection elements
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Thermocouple
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Thermocouple
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A Thermocouple is a sensor used to measure temperature
Thermocouples consist of two wire legs made from different metals
The wires legs are welded together at one end, creating a junction
This junction is where the temperature is measured
When the junction experiences a change in temperature, a voltage is created
The voltage can then be interpreted using thermocouple reference tables to calculate
the temperature
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Working principle of thermocouples
• When two wires composed of dissimilar metals are joined at both ends and one of the
ends is heated, there is a continuous current which flows in the thermoelectric circuit
• If this circuit is broken at the centre, the net open circuit voltage (the Seebeck voltage)
is a function of the junction temperature and the composition of the two metals
• When the junction of the two metals is heated, or cooled, a voltage is produced that can
be correlated back to the temperature.
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Working principle of thermocouples
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Working principle of thermocouples
• A time constant has been defined as the time required by a sensor to reach 63.2% of
a step change in temperature under a specified set of conditions
• Five time constants are required for the sensor to approach 100% of the step change
value
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Thermocouple
• There are many types of thermocouples, each with its own unique characteristics in terms
of temperature range, durability, vibration resistance, chemical resistance, and application
compatibility
• Type J, K, T, & E are “Base Metal” thermocouples, the most common types of
thermocouples
• Type R, S, and B thermocouples are “Noble Metal” thermocouples, which are used in
high temperature applications
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Thermocouple applications
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Power Generation
Oil/Gas
Pharmaceutical
Cement
Paper & Pulp
everyday appliances like stoves, furnaces, and toasters
K-Type thermocouple for ovens
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Furnace thermocouples
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Thermocouple, RTDs, thermistors
• Thermocouple generally can measure temperatures over wide temperature ranges,
inexpensively, and are very rugged, but they are not as accurate or stable as RTD’s and
thermistors
• RTD’s are stable and have a fairly wide temperature range, but are not as rugged and
inexpensive as thermocouples
• RTD’s are subject to inaccuracies from self-heating
• Thermistors tend to be more accurate than RTD’s or thermocouples, but they have a
much more limited temperature range
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Relay
• A relay is an electronically operated switch that is remotely activated by an
electromagnet which pulls a set of contacts to either make or break a circuit
• Electrical relays are commonly used for switching signals, radio frequencies, high
current circuits when using a lower current circuit, and loads such as resistive, motor,
lamp, inductive, and capacitive applications
• This is helpful when an in-line switch or existing circuit does not have the capacity to
handle the required current.
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Actuators
• Pneumatic actuators are devices that convert the energy of compressed air or gas into a
mechanical motion that regulates one or more final control elements.
• The motion of a pneumatic actuator may be linear or rotary depending on the device’s
design
• Prototypical actuators use an external compressive force, such as compressed air or
gas, to move a piston along the inside of a hollow cylinder and build pressure. This
generates a linear force relative to the piston’s pressure differential multiplied by its
surface area, which is used to move a load along a straight line
• Rotary pneumatic actuators differ from linear designs in that torque is generated as
opposed to a linear motion. This can be accomplished by transferring the linear motion
of a piston to a rotating component, or vice versa
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1) Single Acting Cylinders
2) Double Acting Cylinders
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3) Rotating Cylinders
4) Cylinder with Cushioning
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Pneumatic Solenoid Valve
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Pneumatic Solenoid Valve
3/2 Valve
• A 3/2 way valve has 3 ports (inlet and outlet) and two positions (open or
closed)
• 4/2 Valve
•5/2 Valve
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Method of operation of Control Valves:
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