Transcript Ppt0000002

Programmable Logic Controller
(PLC)
Contents
Control Process
 What is PLC?
 General Architecture of PLC
 PLC Operating Cycle
 PLC Hardware Type
 PLC Architecture Evolution
 Programming of PLC
 Basic PLC Advantages
 Applications

Control Process
Physical Quantity is sensed in the form of small
current/voltage e.g. Temperature, Pressure, Flow,
Level etc (Sensor)
 This Electrical Signal is amplified to a certain level
(Amplifier)
 Then amplified analogue output is converted into
digital form. (Analogue to Digital Converter i.e.
A/D)
 This digital output is fed to the controller of the
system to control the various physical quantities
with the help of different devices. (PLC,
Microcontroller, DSP etc…)

Block Diagram
Physical Quantity
Amplified
Analogue output
Amplifier
A/D
(Temperature, Pressure etc..)
Digital
Analogue output
in mA/mV
Controller
(PLC, Microcontroller etc…)
Control signals
Digital /Analogue
Devices
(Motors etc…)
What is PLC?
A digitally operating electronic apparatus
which uses a programmable memory for
internal storage of instructions
 Implement specific functions, such as logic,
sequencing, timing, counting and arithmetic
 Control various types of machines or
process through digital or analogue
input/output.

Traditional concept of PLC

PLC performs relay equivalent functions

PLC performs ON/OFF control

Designed for industrial environment
General Architecture of PLC
PLC Operating Cycle
PLC Signal Flow
Output
PLC Hardware Type


A most basic PLC system is a self contained PLC which has
two terminal blocks, one for the Input and other for the
Output, called “Micros”.
Typically they provide front panel LED status indication of
I/O and processor status.
2. Modular Chassis Based PLC

The vast majority of PLC’s installed today are
modular chassis based PLC consisting of:
3. Modular Chassis-less PLC Systems
The advanced PLC’s are chassis-less
 These are modular PLC systems.
 These systems also have:
-Processor
- Power supply
-I/O modules
-Communication card
 These components mount directly on a
panel to allow easy insertion and removal.

General PLC Blocks
Personal Computer
220V, 50/60Hz
Power
Supply
CP
U
RS 232
Communicat
-ion Module
AC to DC conversion (12V or 48V)
Analogue
Input
Analogue
Output
Digital
Input
Digital
Output
Contd…
Contd…
48V DC
Contd…
48V DC
Contd…
Contd…
Bus system is
PLC Architecture Evolution
PLC Architecture Evolution
PLC Architecture Evolution
PLC Architecture Evolution
PLC Architecture Evolution
PLC Architecture Evolution
Programming of PLC
The purpose of a PLC program is to
control the state of outputs based on the
current condition of the inputs.
Types of programming :

Ladder Logic (Analogous to Relay Technology)
 Function Block (FB’s based on AND-OR logic)
 Visual Basic (VB based on C language)

*DOS based programming (Old Technology)
1. Ladder Logic
Most popular and most commonly used
PLC language is known as “Ladder Logic” .
 Ladder Logic purposely resembles relay
logic.
 In order to control a process we try to
design the logical continuity from input to
output of program.

Ladder Logic Concepts
Line
Neutral
Ladder Logic Concepts
Ladder Logic Concepts
Read and Write Instruction
Read Instruction
Write Instruction
Some Important Instructions

Latching/Unlatching Instruction:
Latch
Retain the output energized until reset
Unlatch
Timer Instructions

Timer ON Delay(TON)

Timer OFF Delay(TOF)

Retentive timer-on delay(RTO)
Counter Instructions

Counter Up (CTU)

Counter Down (CTD)
Comparison Instructions






Equal (EQU)
Not Equal (NEQ)
Less Than (LES)
Less Than or Equal (LEQ)
Greater Than (GRT)
Greater Than or Equal (GEQ)
Some other instructions are Sequencer Instruction, Shift Register Instruction
etc…
Function Block

A
B
Based on pre-defined blocks of various
functions
AND
Basic PLC Advantages
Ease of Programming
 Ease of Maintenance
 Designed for Industrial Environment
 Suitable for Extreme Environmental
Conditions
 Quick Installation
 Adaptable to Change

Applications