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Basic Architecture Of PLC
BLOCK DIAGRAM
Input module
Power supply
Memory
CPUOutput module
Programming unit
M
S
What is a PLC? …. slide1
A PLC is an Industrial Computer. Just like our Personal Computer it has Inputs and Outputs.
Some of the Inputs to the PLC are:Limit Switches.Float Switches.Push Buttons.Photoelectric Sensors.Pressure Switches.
Temperature Sensors.Pressure Sensors.
Discrete input control field devices
Analog input control field devices
Some of the Outputs to the PLC are: Motor Starters Pilot Lights Solenoids.
Formal Definition of PLC.
The formal definition of PLC comes from the National Electric Manufacturers Association (NEMA).
“A PLC [Programmable Logic Controller] is a digitally operated electronic system, designed for use in an industrial environment, which uses a programmable memory for the internal storage of user-oriented instructions for implementing specific functions such as
Logic Sequencing Timing Counting & Arithmetic…………………
to control, through digital or analog inputs and outputs, various types of machines or processes.
Fig-2 shows how a human being is involved with the PC.
How a Human Being is Involved with PLC?
PLC Hardware Configuration: 2 Types.
1] Fixed/ Composite PLC 2] Modular PLC
Allen Bradley SLC 500 Modular PLC
Power supply Processor Input modules Output module
Slot 0 Slot 2Slot 1 Slot 3
Interfacing of the PLC with Programming Units.
Personal Computer
RS 232
1747- PIC
1747- C10 cable
SLC – 500 PLC ( Modular )
Output modulePower supply Processor
Slot 0 Slot 2Slot 1 Slot 3
Input modules
1 2 3 4 5 6 C7 1110980 12 13
0 1 2 3 4 5 6 7 8 9
Power
RunForceCommunication
MicroLogix 1200
OUT
IN
Allen Bradley MicroLogix 1200 Fixed PLC
24 Volts
Power Supply
Motor
Starter
L2
PLC InputSection
PLC O/PSection
Sensor input to PLC
PLC Output to Motor Starter
Sensor
Input Module
24 VDC Power Supply
+
-
0
12
3
4
6
5
C
7
Input signal from limit switch to input screw terminal 0 on a 24 VDCinput module.
Just take a glance at the input module wiring with limit switch!!!
What Do You Mean By Sinking & Sourcing?
Solid State input devices with NPN transistors.Sinking Input Devices
Sourcing Input DevicesSolid State input devices with PNP transistors.
Sinking & Sourcing are the terms used to describe current flow through a field device in relation to the Power Supply and the associated I/O points
What Do You Mean By Sinking & Sourcing?
Input Module
24 VDCPowerSupply
-
+
Sinking Switch
Sourcing ModuleInput Module
Sourcing Switch
Sinking Module
24 VDCPowerSupply
+
-
Wiring Diagrams of AB SLC 500 1746-IV8 ………Sourcing I/P.
Input Module
01
2
3
4
6
5
C
7
- 24 VDC
+ 24 VDC
Input Module
24 VDCPowerSupply
-
+
Sinking Switch
Sourcing Module
Input Module
01
2
3
4
6
5
C
7
+ 24 VDC
- 24 VDC
Wiring Diagrams of AB SLC 500 1746-IB8 ………Sinking I/ P.
Input Module
Sourcing Switch
Sinking Module
24 VDCPowerSupply
+
-
Input Modules: Classification…………..
Discrete Input modules Analog Input Modules
Discrete AC input modules.
Discrete DC input modules.
Input Modules
The main Function of the Input module is…………
To take the field device Input signal.
Electrically isolate it. and
Send by the way of backplane board to the CPU.
Discrete DC Input Modules.
The most common module types available are listed below
24 VDC48 VDC10 - 60 VDC
120 VDC 230 VDC Sink/ Source 5 - 50 VDC
5 VDC TTL level5/12 VDC TTL level
Block Diagram of typical Discrete DC Input Circuit.
Module OperationDC input
Optical Isolation
Noise &debounce
Filter.
ThresholdDetector.
Logic
CPUInputStatus
File
LED
1 2 3
4
56
7
8
Simplified Circuitry of a DC Input Module
Discrete AC Input Modules.
The most common module types available are listed below
24 VAC48 VAC
120 VAC 240 VAC Nonvoltage
120 Volts Isolated 240 Volts Isolated
24 VAC/DC
Block Diagram Of Typical Discrete AC Input Circuit
Noise and
debounce filter
Bridge rectifier
Optical isolation
Input status table
Logic CPUThreshold detector
LED
To PC Internal sys. 1
AC
2
3Pulsating DC
4
5Filtered DC
6 7 8 10
9
11
OPTICAL Isolator is used to isolate high voltage incoming signals from the CPU’s lowervoltage levels. It protects the low voltage CPU and its associated circuitry by preventingspikes or high – voltage transients on the input circuit from transferring into the low voltagecircuitry.
Power file Conversion CircuitOptical Isolation CircuitLogic Circuit
Two Types of Discrete Input Device………….
Mechanical Devices Electronic Devices Limit Switches.
Toggle Switches
Selector Switches
Push Button
Contacts from an Electro-Mechanical relay. etc
Solid - State sensors like
Inductive Proximity device.
Capacitive Proximity device.Etc.
Binary Concept & Binary Data Representation……… slide1
Bit Position
4 Bits = 1 Nibble
Bit
0 0 l l 0 l 0 l l l l 0 0 1 0 02 03456789101112131415 1
8 Bits = 1 Byte
16 Bits = 1 Word
Information can be represented by arranging the 1s and 0s in different combinations within a 16 bit word.
Binary Concept & Binary Data Representation……… slide2
LSB
0 0 l l 0 l 0 l l l l 0 0 1 0 02 03456789101112131415 1
MSB= Most Significant Bit = Least Significant Bit
In the Next slide we will have a look ………. How a 16-bit word is used to represent the ON-OFF status of each screw terminal on a 16-point I/ O module.
Correlation of 16 bit Words to Input Signals………slide1
15 2 034567891011121314 1
Input Module
01
23
4
65
C
78
9
12
1011
1413
15
One LED for each input point. LED is ON when there is an ON signal to the corresponding input point
Correlation of 16 bit Words to Input Signals……….slide 2
Input Module
01
2
3
4
6
5
C
7
150 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0
2 034567891011121314 1
+ 24 VDC
- 24 VDC
Unused bits
One LED for each input point. LED is ON when there is an ON signal to the corresponding input point
Correlation of 16 bit Words to Input Signals……….slide 3
Slot 0 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6
0002
0806
12
04
14com
10
020406
VAC08101214
VAC
00
0911
01
0507
03
1513
0911
01
0507
03
15com
13
Power Supply CPU Input Module Output Module Input Module Output ModuleInput Module Input Module
0002
0806
12
04
14com
10
0002
0806
12
04
14com
10
0002
0806
12
04
14com
100911
01
0507
03
15com
13
0911
01
0507
03
15com
13
0911
01
0507
03
1513
020406
VAC08101214
VAC
00
0911
01
0507
03
15com
13
Input Status Table
Word 3
Word 4Word 6
Word 1
Slot 0 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6
0002
0806
12
04
14com
10
020406
VAC08101214
VAC
00
0911
01
0507
03
1513
0911
01
0507
03
15com
13
Power Supply CPU Input Module Output Module Input Module Output ModuleInput Module Input Module
0002
0806
12
04
14com
10
0002
0806
12
04
14com
10
0002
0806
12
04
14com
100911
01
0507
03
15com
13
0911
01
0507
03
15com
13
0911
01
0507
03
1513
020406
VAC08101214
VAC
00
0911
01
0507
03
15com
13
Output Status Table
Word 5
Word 2
Correlation of 16 bit Words to Output Signals……….slide 4
PLC Memory and How it is used?………………….slide 1
Input module
Power supply
Memory
CPUOutput module
M
S
Personal Computer
PLC Memory.
We are already familiar with the basic Block diagram of Architecture of PLC.
PLC Memory and How it is used?………………….slide 2
System Memory Application Memory
Data Memory
User Memory
User Programs
Data Files
The Executive
“The Personality”
[ ROM ]
[Non- Volatile]
[ RAM ]
Volatile
PLC Memory
Application Memory……………………. Slide 1
File 0 Output Status File
File 1 Input Status File
File 2 PLC Status Bits
File 3 Internal Bits
File 4 Timer
File 5 Counter
File 6 Control
File 7 Integers
File 8 Floating Point Data
File 9 Common Interface
File 10 - 255 User Configurable
1] DATA Memory
DATA Files
Application Memory……………………. Slide 2
2] User Memory
File 0 System Program File
File 1 Reserved File
File 2 Main Ladder Program File (LAD2)
File 3 User Error Fault Routine
File 4 High Speed Counter Interrupt File
File 5 Selectable Timed Interrupt
File 6 - 15 Subroutine Ladder Program
This is the File where we will do Programming in LD Language………( Ladder Diagram)
Output Modules: Classification…………..
Discrete Output modules Analog Output Modules
Solid state OutputRelay Output
AC O/P Modules DC O/P Modules
•12, 24, 48 VAC
•120 VAC
•230 VAC
•TTL Level
•12, 24, 48 VDC
•120 VDC
•230 VDC
• 24 VDC sink
• 24 VDC source
•Relay contact
•Isolated Relay contact
•Relay contact Output
LOAD
Output Module
0
1
2
3
110 VAC
User supplied power for field devices
COMSignal from CPU Operates switch
Basic wiring for 120 VAC discrete output module
S/G Flow from CPU through an output module to the field device
CPU solves ladder
program
Output status table
Chassis backplane
Module logic circuits
Optical Isolation
Module Screw
Terminal
Field Device
Block Diagram of a Typical Output module
LatchLogic
CircuitryOptical
isolation
Triac switching circuitry
Filter
FUSE
Controlleddevice
LED
Simplified Single point Relay Output
LOAD
ON or OFF signalfrom output status table
Output Module
L-1 L-2
Relay Switching Device
Common to other output points
Sinking Output module Interface with Field Device.
Sinking Output Module
VDCOut 0Out 1Out 2Out 3Out 4Out 5Out 6Out 7
DC Com
+ DC
DC Common
Sourcing Output module Interface with Field Device.
Sourcing Output Module
VDCOut 0Out 1Out 2Out 3Out 4Out 5Out 6Out 7
DC Com
+ DC
DC Common