This document provides an overview of programmable logic controllers (PLCs). It discusses how PLCs improved upon earlier relay logic control systems by being more reliable, flexible, and efficient. The key components of a PLC are described, including the programming device, input/output tables, processor, memory, and power supply. PLCs operate on scan cycles that read inputs, run the user program to determine outputs, and refresh the outputs. Common PLC manufacturers are then listed.

1. PROGRAMMABLE LOGIC
CONTROLLER(PLC)

2. CONTENTS
•
•
•
•
•
•
•
•
•
RLC
Ladder logic
Disadvantages of RLC
PLC
Its components
Operation cycle
Information Flow
Types
Manufacturers

3. RELAY LOGIC CONTROL
• Before the invention of the Programmable Logic
•
•
•
Controller (PLC), most industrial control was
done using relay control panels.
Relay logic is a method of controlling industrial
electronic circuits by using relays and contacts .
Switches and relays can be arranged in circuits
to make logical decisions.
It uses ladder logic.

4. LADDER LOGIC USING LINE
DIAGRAM-1
AND Logic
X
Y
Z
(
)
OR Logic
X
Z
(
Y
)

8. Problems with relay control
panels
• Mechanical Relays and switches failed regularly
•
•
•
(coil failure, contact wear and contamination,
etc.)
Difficult to diagnose problems and replace relays
and switches
Difficult to change hardwired logic (example:
changing an “OR” circuit to “XOR”)
Consumed a lot of power.

9. Architecture of PLC
Programming
Device
Input
Table
User
Program
Output
Table
Data
Storage
Input
Devices
Input/Output
System
Output
Devices

10. What are PLC’s component?
Programming / Communication
Devices
I
n
p
u
t
Optical
Isolation
Barrier
C
i
r
c
u
i
t
s
Central
Processor
MEMORY
program
data
Low Voltage
POWER SUPPLY
O
u
t
p
u
t
C
i
r
c
u
i
t
s
CR???????
Optical
Isolation
Barrier

11. What' happens in an operating
START
cycle?
1.Input
3. Output
Scan
Based on the data in
the output image file
the PLC energises or
de-energises it’s output
circuits,controlling
external devices.
- -PLC
OPERATING
CYCLE
TYPICALLY
1 to 25 ms.
2. Program
Scan
Scan
During the input scan PLC
examines the external input devices
-On or Off.
The status of the inputs is
temporarily stored in an input image
memory file.
The PLC scans the instructions in the ladder
logic program,uses the input status from the
input image file & determines if an output will
be energised.The resulting status of the outputs
is written to the output image memory file.

12. Information
Information Flow…
Internet
Internet
Webcast
Server
Web Server
&
Firewall
Email
from
PLC-1
Failure
Report
Ethernet TCP/IP
!
Switch/Router
!
Control
Ethernet TCP/IP
Modbus
!
ASi
BusX
BusX

13. MANUFACTURERS•
•
•
•
•
•
Modicon
Schneider Electric
General Electric
Mitsubishi
Allen Bredley
Seimens

14. Thank you
ALI
BYMUSTAHID