tự động hóa càng ngày càng phát triển , và tiêu biểu cho tự động hóa là công nghệ PLC. đây là tài liệu nói về PLC bằng tiếng anh chuẩn, sẽ mang đến cho bạn đọc những khái niệm cơ bản về PLC theo tiêu chuẩn quốc tế, nên sẽ được trình bày bằng tiếng anh.
Trang 1Chapter 1:
Introduction to PLC
11/09/2016 Programmable Logic Controller
1
Faculty of Electrical and Electronics Engineering
Department of Automation Control
Lecturer: Nguyen Tan Doi
Trang 2Objectives
2
Upon completion of this chapter, students will be able to:
Describe the components of a PLC
Understand the PLC specifications
Apply PLC to industrial systems
Convert a hardwired system to a PLC system
Show the areas can be use PLC
Trang 3Content
11/09/2016 Programmable Logic Controller
Trang 5Definition of PLC
11/09/2016 Programmable Logic Controller
5
What is a PLC?
Programmable Logic Controller
Solid-state control system
Control the devices based on user program
Definition of PLC
Digital electronic device
Use a programmble memory to store the instructions and to
implement the specific functions
A computer designed to work in industrial enviroment
Trang 6Definition of PLC
6
Trang 7What is CONTROL
11/09/2016 Programmable Logic Controller
7
The proccess in a system
One or more input variables influence the other
variables
Trang 8History of PLC
8
In late 1960s, General Motors was interested in the
computer application to replace the hardwired systems
Bedford Associates –Modicon and Allen Bradley
responded to General Motors
The name given was “Programmable Controllers” or PC
Programmable Logic Controller or PLC was a
registered trademark of the Allen Bradley
Later, PC was used for “Personal Computer” and PLC for “Programmable Controller”
Trang 9Advantages of PLC
11/09/2016 Programmable Logic Controller
9
Less wiring
Wiring between devices and relay contacts are done in the PLC program
Easier and faster to make changes
Trouble shooting aids make programming easier and
reduce downtime
Reliable components make these likely to operate for
years before failure
Trang 10Comparision
10
The functions are determined by the
Can be contact circuits (relay, contactor)
or logic circuits (electronic devices)
Consist of a control device which connected to sensors and actuators
Trang 11PLC Operation
11/09/2016 Programmable Logic Controller
11
While a PLC is running, there are 4 steps repeated continueously:
1) Self test: Testing of its own hardware and
software for faults
2) Input scan: Scan all inputs, PLC will copy all
the inputs and copy their values into memory
3) Program excution:
The logic program is solved
4) Output scan: The output values are updated
after a scan cycle, then energized or
de-energized ouputs
Self Test
Input Scan
Program Excution Output
Scan
Trang 12How does a PLC work
12
The sensors are connected to the Input modules
The Processor excutes the program in memory and scan the
individual input for presence or absence of voltage
Depend on the state of inputs, the processor directs voltage to
Trang 13PLC signal flow
11/09/2016 Programmable Logic Controller
13
Programming Terminal
O:0/7 O:0/7
O:1/5
Output Devices
Output Modules Processor Memory
Input Module
Input Devices
Ladder Program
O:0/7 O:1/5
I:0/6 I:1/4
O:1/5
I:0/6
I:1/4 I:0/6
I:1/4
Data
Input Image Table
Output Image Table
Trang 14Components of PLC
14
There are five components in a PLC
The PLC processor, or CPU
I/O (Input /Output) modules
Chassis and backplane
Power supply
Programming software
Trang 15Components of PLC
11/09/2016 Programmable Logic Controller
15
Trang 16Components of PLC
16
CPU-Central Processing Unit
The CPU reads the input signal states, processes the
user program and controls the outputs
The CPU provides internal memory, timers and
counters
Executes the user program
Commands influence outputs to change state based on program execution For example: Turn a light on, start a fan, adjust a motor’s speed, or temperature, …
Trang 17Components of PLC
11/09/2016 Programmable Logic Controller
17
Input/ Output Modules
switches and sensors
Input modules convert different types of electrical
signals such as, 24V/0-10V/4-20mA, to signals which the controller can understand
to a signal that an electrical device needs to operate
There are different types of output devices, so a wide
variety of output cards available, including both digital and analog cards
Trang 18Input Circuits
18
Trang 19Input Devices
11/09/2016 Programmable Logic Controller
Trang 20PNP Sensor
20
Trang 21NPN Sensor
11/09/2016 Programmable Logic Controller
21
Trang 22Output Circuits
22
AC Output
Trang 23Output Devices
11/09/2016 Programmable Logic Controller
Trang 24Components of PLC
24
Chassis and backplane
All PLCs need some method of communicating between the controller and Input/Output/communications modules
Three ways used to accomplish these communications:
Modular PLC: CPU slides into a chassis with other modules
chassis repuired
PLC with the modules built in, comes as one block
Trang 25Chassis and Backplane
11/09/2016 Programmable Logic Controller
25
Trang 26 Power supply modules that fit into one of the slots in a chassis
Stand alone power supplies that connect to the PLC or I/O
through a power cable
Embedded power supplies that come as part of the PLC block
Trang 27Components of PLC
11/09/2016 Programmable Logic Controller
different languages, LAD, STL, FBD, …
Trang 28Types of memory
28
Alterable
UV erasable EPROM / REPROM
Electrically erasable EEPROM / EAPROM
Semiconductor
Trang 29PLC Memory
11/09/2016 Programmable Logic Controller
29
Trang 30Input Table
30
Trang 31Output Table
11/09/2016 Programmable Logic Controller
31
Trang 32Storage Area
32
Trang 33Example
11/09/2016 Programmable Logic Controller
33
Trang 34Results of Operation PLC
34
Trang 35Digital and Analog
11/09/2016 Programmable Logic Controller
35
Analog representation: a quantity is represented by a
continuous variables, proportional indicator
Analog signals are expressed by 0-4mA, 0-5V/10V, …
Analog signals are easily converted from physical quantities
Digital representaton: the quantities are represented not
by continuous variable but by symbols called Digits
Digital signals are expressed by 0 and 1
Digital signals are made by electronic circuit
Analog = Continuous
Digital = Discrete
Trang 36Digital and Analog modules
Analog Input (AI) modules adapt analog process
signals, e.g, from transducers, convert them to digital
values ADC
Analog Output (AO) modules convert internal digital
values of the PLC to analog process signals e.g
temperature controller DAC
Trang 37Digital and Analog modules
11/09/2016 Programmable Logic Controller
37
Digital modules use only a single bit to represent the
state of the device
For example, a switch is either open or closed Therefore, the
bit is either a 0 (switch is open) or a 1 (switch is closed)
Analog modules use words to represent the state of a
device An analog signal represents a value
For example, the temperature could be 0, …, 90, etc degrees Analog modules use a value, such as 0, …, 14000, rather than a
0 or 1 to represent the state of the device
Trang 38PLC Applications
38
o Hardwired arrays of relays were used to control the operation of heavy machines that contain motors and other high power devices
o Originally PLCs were used to substitute the switching relay
networks used in industrial applications,
o Now they can be used implement other tasks such as timing,
counting, calculating, comparing and processing of analog signals
Trang 3911/09/2016 Programmable Logic Controller
39
Trang 4040
Trang 4111/09/2016 Programmable Logic Controller
41
Trang 4242
Trang 43Question and Answer
11/09/2016 Programmable Logic Controller
43
Trang 44Question and Answer
44
Trang 45Question and Answer
11/09/2016 Programmable Logic Controller
45
Trang 46Problems
46
Sketch the connections needed for Inputs and ouputs:
Trang 47Problems
11/09/2016 Programmable Logic Controller
47
Trang 48Problems
48