Industrial Automation
PLC Architecture
Programmable Logic Controller
PLC
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 1
Industrial Automation
PLC Architecture
PLC Definition
•
•
•
•
•
•
•
PLC is a
user friendly,
microprocessor
based,
specialized computer
that carries out
control functions
of many types
and levels of
complexity
DEFINE THE PLC ARCHITECTURE
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 2
1
Industrial Automation
PLC Architecture
More PLC characteristics (I)
•
Typical wired relay control
Flexibility
– Same PLC model in
different machines
– Implementing changes and
correct errors
• Change program
• Versus rewiring
connections
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 3
Industrial Automation
PLC Architecture
More PLC characteristics (II)
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Lower cost
– Increased technology makes it possible to condense more
functions into smaller and less expensive package.
Pilot running
– A PLC based control can be prerun and evaluated in the office or
lab.
Reliability and Maintainability
– Solid-states devices are more reliable, in general, than mechanical
systems or relays and timers.
– Consequently, the control system maintenance costs are low and
downtime is minimal.
Ladder or Boolean Programming Method
– The PLC programming can be accomplished in the ladder mode
(similar to wired relay) by an electrician or technician (not complex
automation)
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 4
2
Industrial Automation
PLC Architecture
Basic Module Architecture
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•
Central processing unit (CPU)
– The heart of the system: processes data, carries out the logic
operations
I/O Modules
– Input modules
• Takes input front the outside world (plant)
• Protects the CPU from the outside world (Optical Isolation)
– Output modules
Power supply
• Provides output voltages to energize motor starters, lights, coils, valves
I/O modules
CPU
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 5
Industrial Automation
PLC Architecture
Connection example (motor control)
•
Integrated CPU
General
Run
Temper
VCC
E124.0
E124.1
VCC
PLC
A124.0
A124.1
E124.2
A124.2
GND
GND
Prof. José A. Rodríguez Mondéjar
BTemper
Motor relay
UPCO ICAI Departamento de Electrónica y Automática 6
3
Industrial Automation
PLC Architecture
Modular architecture
•
The PLCs are expandable. Expansion modules contain
additional inputs and outputs. These are connected to the
base unit using a ribbon connector or a rack.
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 7
Industrial Automation
PLC Architecture
PLC Digital Input Module layout
•
The input module perform four tasks electronically:
– Senses the presence or absence of an input signal at each of its
input terminals.
• The input signal tells what switch, sensor or other signal is on or off in
the process being controlled
• Standard levels: 24VDC, 110AC, 220AC, 4-20mA
– Converts the signal for on, or high to a DC level usable
– Carries out electronic isolation
– Produces an output to be sensed by the PLC CPU
Optoisolator
Prof. José A. Rodríguez Mondéjar
Filter (50 Khz) Converter
Terminal
UPCO ICAI Departamento de Electrónica y Automática 8
4
Industrial Automation
PLC Architecture
PLC Digital Output Module Layout
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A DC signal from the CPU is converted through each
module section (terminal) to a usable output voltage, either
AC or DC (voltage or current)
– Standard levels: 24VDC, 110AC, 220AC, 4-20mA
Logic
Input
Prof. José A. Rodríguez Mondéjar
Optoisolator
Converter
UPCO ICAI Departamento de Electrónica y Automática 9
Industrial Automation
PLC Architecture
Digital Output module Classification
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•
Relay
Transistor
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 10
5
Industrial Automation
PLC Architecture
Other modules
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Analog Input/Output modules
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± 10 volts
0...10 volts
0...20 mA
4...20 mA
Important point: speed acquisition / precision
PID module
Network module
ASCII module
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 11
Industrial Automation
PLC Architecture
Internal Block Diagram of a PLC (I)
NETWORK
TIMERS
Processor
COUNTERS
INPUT
MODULES
Prof. José A. Rodríguez Mondéjar
CLOCK
ROM
RAM
OUTPUT
MODULES
UPCO ICAI Departamento de Electrónica y Automática 12
6
Industrial Automation
PLC Architecture
Internal Block Diagram of a PLC (II)
•
•
Processor
– The computer center that carries out the logic operations (also
arithmetic)
Memory
– The area of the CPU in which information is stored and
manipulated
– ROM (Read Only Memory)
• Operating System
• System Data
– RAM (Random Access Memory)
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User data
Copy of input signal states
Copy of output signal states
Counters
Timers
User program
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 13
Industrial Automation
PLC Architecture
Internal Block Diagram of a PLC (III)
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•
Clock
– Clock speed determines how quickly microprocessor executes
instructions.
Communications
– RS232
• Programming equipment: Personal computer
• Short distance
– RS485 or similar
• Connection with other equipment
• Long distance/noise immunity
– PROFIBUS
– FIPBUS
– MODBUS
– MPI
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 14
7
Industrial Automation
PLC Architecture
How does PLC work?
•
Like a computer:
– Operating System (Real Time Operating System RTOS)
– Executes User Control Program
main() {
PLC
int i1, i2, f;
while (1) {
VCC
Input1
Input2
VCC
Read Inputs;
E124.0
A124.0
E124.1
A124.1
Execute user program;
E124.2
GND
Write Outputs;
A124.2
GND
}
}
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 15
Industrial Automation
PLC Architecture
PLC Example
•
Input1
Input2
Like a computer:
– Keyboard is the input signals for plant
– Screen is the output signals to the plant
main() {
PLC
int i1, i2, f;
while (1) {
Input1
Input2
VCC
i1=Read(Input1);
VCC
E124.0
i2=Read(Input2);
A124.0
E124.1
A124.1
f=i1&&i2; %AND
E124.2
GND
Write(f,Output1)
A124.2
GND
}
}
Prof. José A. Rodríguez Mondéjar
User Control Program
UPCO ICAI Departamento de Electrónica y Automática 16
8
Industrial Automation
PLC Architecture
Example running
Event Loss
Scan time
Input1
Input2
Output1
i1
i2
f
CPU
SO
USER
CONTROL
PROGRAM
Null Task
Read Inputs
Prof. José A. Rodríguez Mondéjar
Write Outputs
UPCO ICAI Departamento de Electrónica y Automática 17
Industrial Automation
PLC Architecture
SCAN CYCLE
INPUT
TERMINALS
INPUT
STATUS
TABLE
INPUT SCAN:
Input terminals
are read and
inputs status
table is updated
accordingly
Prof. José A. Rodríguez Mondéjar
USER
PROGRAM
OUTPUT
STATUS
TABLE
PROGRAM SCAN:
During program scan,
data in input table is
applied to user program,
program is executed and
output table is updated
accordingly
OUTPUT
TERMINALS
OUTPUT SCAN:
Data associated
with output
status table is
transferred to
output terminals
UPCO ICAI Departamento de Electrónica y Automática 18
9
Industrial Automation
PLC Architecture
IMPORTANT
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ANY changes in the status of input devices during the
program or output scan are not recognized until the next
input scan
Data changes in the output table are not transferred to the
output terminal during the input and program scans. The
transfer affecting the output devices takes place only
during the output scan.
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 19
Industrial Automation
PLC Architecture
Do you understand?
•
Output?
– 0 permanent
– 1 permanent
– 0101010…
main() {
int i1, i2, f;
PLC
while (1) {
i1=Read(Input1);
VCC
Input1
Input2
i2=Read(Input2);
E124.0
VCC
A124.0
E124.1
f=i1&&i2; %AND
A124.1
E124.2
f=i1||i2; %OR
A124.2
GND
GND
Write(f,Output1)
}
}
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 20
10
Industrial Automation
PLC Architecture
HOW TO PROGRAM A PLC?
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High level language?
Control System
– C Language
– Difficult to program
•
Process
• Pointers!!
Language near technicians
background
PLC
– Easy to program
– Standard
– Flexible
Serial
communication
• Easy and complex languages
in the same PLC
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 21
Industrial Automation
PLC Architecture
IEC 1131-3 Standard
•
The IEC standard specifies the following programming
languages
Instruction List
AND
A
ANDN
B
=
C
Sequential Function Chart
(GRAFCET)
0
Structured Text
Init
C:= A AND NOT B
1
Stopped
Run
2
Function Block Diagram
3
AND
A
Fill
Prof. José A. Rodríguez Mondéjar
Heat
Hot
C
B
Ladder Diagram
Full
4
Empty out
A B
C
-| |--|/|----------------( )
Empty
UPCO ICAI Departamento de Electrónica y Automática 22
11
Industrial Automation
PLC Architecture
Memory model
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15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0 7 6 5 4 3 2 1 0
– Instructions
– Data: Memory
Matrix
– 8 bits x Address number
– 16 bits x Address number
Accessing methods
– Bit M0.3
• Work with logical variables
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– Byte: MB0
– Word: MW0, MW2.
– Long word: MD0, MD4
Telemecanique uses
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•
MD0
MW0
Industrial Automation
Digital Input Table
– E124.0, EB124, EW124 (Siemens)
– I124.0, IB124, IW124 (IEC)
– Remember the difference between real
input and input variable in the program.
Digital Ouput Table
– A124.0, AB124, AW124 (Siemens)
– Q124.0, QB124, QW124 (IEC)
Input
Table
Output
Table
M255
E127
A127
·····
– M0.1, MB3, MW4, MD0
– User variables
User
Table
·····
Memory
·····
•
MB0
M3.2
UPCO ICAI Departamento de Electrónica y Automática 23
Variable Types or Table Types
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MB5
8x16 Memory
PLC Architecture
•
MW8
8 bit
– %MW0
Prof. José A. Rodríguez Mondéjar
MD12
M1
M0
E1
E0
A1
A0
Timers
Counters
T127
Z63
Timer Table
– T1 (16 bits timer
– The value increases by clock
Counter Table
– Z5 (16 bits counter
– Event count
Prof. José A. Rodríguez Mondéjar
·····
•
Components of the PLC
program:
·····
•
T1
T0
Z1
Z0
UPCO ICAI Departamento de Electrónica y Automática 24
12
Industrial Automation
PLC Architecture
Ladder Diagram Example
E124.0
E124.1
E124.2
E124.2
Symbol Programming
A124.0
General
A124.1
Térmico
Run
Térmico
Motor
BTérmico
Symbol definition
increases program
readable
VCC
General
Run
Térmico
E124.0
E124.1
VCC
PLC
A124.0
A124.1
E124.2
A124.2
GND
GND
Prof. José A. Rodríguez Mondéjar
BTérmico
Motor
UPCO ICAI Departamento de Electrónica y Automática 25
Industrial Automation
PLC Architecture
Ladder Diagram is only a representation
•
•
The program execution is not
parallel
The execution is instruction
by instruction: in sequence
Segmento 1: Control A124.0
1
E124.0
3
A124.0
E124.1
– The brain of a PLC if a
microprocessor
2
Segmento 2: Control A124.1
4
5
6
Prof. José A. Rodríguez Mondéjar
E124.1
7
A124.1
E124.2
E124.3
UPCO ICAI Departamento de Electrónica y Automática 26
13
PLC Architecture
Industrial Automation
Choose a PLC
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Memory size
Scan Time/Maximum
number of instructions
Integrated functions (PID)
I/O Capability
– Different interfaces with real
world
Flexibility/expandability
– Maximum number of IO
Signals that PLC can
control
Networking
– Non standard protocol
– Vs standard protocol
Cost
Serviceability/support
Training/Documentation
Prof. José A. Rodríguez Mondéjar
UPCO ICAI Departamento de Electrónica y Automática 27
14