Programmable Logic Controllers
Professor Charlton S. InaoDefence UniversityBishoftu ,EthiopiaGuest Professor, Adama Science and Technology UniversityAdama, Ethiopia
Professor Charlton S. InaoDefence UniversityBishoftu ,EthiopiaGuest Professor, Adama Science and Technology UniversityAdama, Ethiopia
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General Objectives To explain and understand the following PLC concept:
Programmable logic controller; Structure of PLC and system components; Programming Languages;( LAD,STL,FBD)Logic Gates application for PLCCounterShift RegisterJumpProgramming Applications
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Programmable Logic Controllers
• Defined by NEMA as a digital electronic apparatus with a programmable memory for storing instructions to implement specific functions (logic, sequencing, timing, counting, and arithmetic) to control machines and processes.
• Considered as the first industrial-based computer
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Advantages of Using PLC
Shorter Project Shorter Project ImplementationImplementation
Easier Modification Easier Modification Without Cost PenaltyWithout Cost Penalty
Design Easily Change Design Easily Change Using SoftwareUsing Software
Project Cost Can be Project Cost Can be Accurately CalculatedAccurately Calculated
Shorter Training Time Shorter Training Time Required Required
A Wide Range of A Wide Range of Control OperationsControl Operations
Easy Easy Maintenance Maintenance
Able to Withstand Able to Withstand Harsh Plant Harsh Plant
EnvironmentEnvironment
High High ReliabilityReliability
Standardization of Standardization of Controller HardwareController Hardware
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Functions of PLC
Sequence Control
Conventional Relay Logic Replacer
Timer and Counter Functions
Auto / Semi / Manual Control of Machines and Processes
Sophisticated Control
Arithmetic Operations
Analog Control (Temperature, Pressure, etc.)
PID (Proportional Integral Derivation)
Stepper / Servo Motor Control
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Functions of PLC
Supervisory Control
Process Monitoring and Alarm
Interfacing with Computers
Factory Automation network
Wide Area Network
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Basic Control System
Open Loop System
INPUT LOGIC OUTPUT
-Pushbuttons
-Limit Switches
-Level Switches
-Flow Switches
-Relays
-Timers
-Counters
-Motors
-Solenoid valves
-Lamps
-Alarm/annunciator
-Relays/contactorsPLC
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Basic Control System
Closed Loop System
ControllerFinal Control
ElementProcessVariable
Transmitter
Set value
Error
Process Variable Primary
Element / Transducer
Temperature
Flow+
_
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Hardware Components
Central Processing Unit (CPU)
Micro PLC – less than 100 I/O’s
Small PLC – 0 to 128 I/O’s
Medium PLC – 0 to 256 I/O’s
Large PLC – 0 to 512 I/O’s
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Power Supply
100 – 240 Volts AC
100 / 110 Volts AC
200 / 220 Volts AC
24 Volts DC
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Inputs
DC – 24 Volts
AC – 110 / 220 Volts
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Outputs
Transistor type (24 Vdc )
Relay / Contact type (24Vdc / 220 Vac)
TRIAC type (110 / 220 Vac)
PNP-type Transistor Input
• Source
•Generates power
NPN-type Transistor Input
• Sink
•Transmits power04/10/23 31
Relay
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Example: Omron Relay
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Peripheral Devices
Programming Console
CX-Programmer Software
Conversion Cables
Connecting Cables
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Software Components1. Ladder Diagram Language – a symbolic instruction type
language
2. Boolean Language- Basic level language that composed of three (3) Boolean logic operation: AND, OR, NOT
Mnemonic Instruction – written in abbreviated form using 3 or 4 letters that generally imply the the operation of the instruction
3. Functional Blocks Language – high level instructions that permit the user to program more complex functions using the ladder diagram format
- Instruction set is composed of blocks that executes or performs specific function04/10/23 37
4. English Statement Language – considered derivative of computer language such as BASIC.
-also known as Control Statements
Note:
OMRON PLC’s uses both Ladder Diagram Language and Boolean Language.
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Key Points to Know in Selecting or Using PLC
I. Know the process to be controlled
II. Determine the type of control
Distributed control
Centralized control
Individual machine control
III. Determine I/O interface requirements
Estimate digital and analog I./Os
Check for I/O specifications
Determine if remote I/O is required
Allow for future expansion
IV. Define peripheral devices04/10/23 39
Steps in PLC Programming
Draw the Schematic Diagram
Draw Control Diagram
Develop PLC Ladder Diagram
I/O Assignment
Convert to Mnemonic (Boolean)
PLC Layout
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Basic Structure of PLC
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PL
C S
pecf
icat
ions
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Programming Format
1) Ladder diagram
2)Mnemonic List
3) Function Block Diagram
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NOR,NAND,EX-OR
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Timer: On delay and Off delay
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Cascaded timer/ On-OFF Cycle Timer
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Two Input control; Resetting a Latch
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Counter
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Shift Register -Mitsubishi
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Shift Register
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i
M 0.0
Q 0.1
Q 0.2
Q 0.3
Q 0.4
Q 0.5
Q 0.6
Q 0.7
Q 0.0
I0.1
0UT
I0.0
I 0.2
M 0.0
M 0.2
M 0.3
M 0.4
M 0.6
M 0.5
M 0.7
SFT
RST
M 0.1
Shift Register Siemens Configuration
END
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Problem: Belt Sanding Machine
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Transfer Station
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End
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