7. DISADVANTAGES OF RELAY
CIRCUTS
Number of hardware will increase with
increase of logic complexity
Relay energizing and de-energizing
takes time
High failure rate
Slow performance
Bulky design difficult to manage
Difficult troubleshooting
9. PLC
What is a Programmable
Logic Controller (PLC) ?
How PLC works ?
What is the need of PLC ?
Hardware involved with
PLC
Advantages of PLC
10. What is Programmable Logic Controller (PLC)
?
CPU
Inputs
Outputs
A PROGRAMMABLE LOGIC CONTROLLER is a solid state
control system that continuously monitors the status of
devices connected as inputs. Based upon a user written
program, stored in memory, it controls the status of devices
connected as outputs.
11. PLC with Distributed I/O
Getting Complex
CPU
Inputs
Outputs
Remote
Outputs
Inputs
12. What is a PLC with Distributed Control?
Getting Really Complex
CPU
Inputs
CPU
Outputs
Outputs
Inputs
Remote
Outputs
Inputs
14. How PLC works?
The CPU contains an “Executive” program that tells
the PLC how to:
Execute the control Instructions
User’s Program
Communicate with other devices
Other PLCs, Programming devices, I/O devices, etc.
Perform Housekeeping activities
Diagnostics, etc
This program is stored in “nonvolatile” memory
Meaning that the program will not be lost if power is
removed
15. How PLC works
START
Four Steps in the PLC Operations
Input Scan
Scan the state of the Inputs
Program Scan
Processes the program logic
Output Scan
Energize/de-energize the outputs
Housekeeping
This step includes communications, Internal
Diagnostics, etc.
Housekeeping
Output
Scan
The steps are continually repeated - processed in a
loop
Input
Scan
Program
Scan
18. Need of PLC
To eliminate the high costs associated
with inflexible, relay-controlled systems.
To Measure input with high speed.
Fast Control (Command and
Regulation).
Robust Protection.
Diagnosis.
19. Advantages of PLC
Compact in size.
Less wiring (Wiring between devices
and relay contacts are done in the PLC
program.)
Easy to implement complex logic.
Faster action and controlling.
Easy troubleshooting.
Easy to implement change in logic.
20. Leading Brands Of PLC
AMERICAN
1.
2.
3.
4.
5.
6.
7.
Allen Bradley
Gould Modicon
Texas Instruments
General Electric
Westinghouse
Cutter Hammer
Square D
EUROPEAN 1. Siemens
2. Klockner & Mouller
3. Festo
4. Telemechanique
JAPANESE
1.
2.
3.
4.
Toshiba
Omron
Fanuc
Mitsubishi