15183.plc (1)

8/16/2019 15183.PLC (1)

1/33

8/16/2019 15183.PLC (1)

2/33

Introduction• Manual Control: Control is said to be done manually when a user performs an action for the

system to function. For example, the user might flip the switch of a manual starter to start and

stop a motor• Automatic Control: Control is said to be automatic when the action is performed automatica

response to a set of conditions.

Machines can be controlled manually or automatically. Usually, there is a combination of manualand automatic control. For example, a process that is started manually may stop automatically

when certain conditions are met.

By: Gurdyal Singh Virk

8/16/2019 15183.PLC (1)

3/33

8/16/2019 15183.PLC (1)

4/33

Control SystemIn terms of output value, a control system can be classified as either Discrete control (Digitalcontrol) or Continuous control (Analog control).

• Discrete (digital) control: The value to be controlled can be either ON or OFF.

Example: Turning a light ON and OFF.

• Continuous (analog) Control: The value to be controlled varies smoothly.

Example: Motor speed.


8/16/2019 15183.PLC (1)

5/33

Types of ControllerDifferent types of controllers could be used based on the requirements of the application. Someexamples are included below:

1. Relays and Contactors: Simple electromechanical devices like relays and contactorswidely used for controlling a discrete manufacturing process


8/16/2019 15183.PLC (1)

6/33

Types of Controller2. Programmable Logic Controllers (PLCs): A Programmable Logic Controller (or PLC) is adigital controller that can control machines and processes. it monitors inputs, makes decisions, an

controls outputs in order to automate machines and processes. Fig demonstrates its function.


8/16/2019 15183.PLC (1)

7/33

Types of Controller3. Microcontrollers ( μCs): Microcontroller is a special purpose computer that can do one job, fexample, the one that is used in an automatic washing machine and in a microwave.


8/16/2019 15183.PLC (1)

8/33

Programmable logic controllerA programmable logic controller (PLC) is a special form of microprocessor-based controllera programmable memory to store instructions and to implement functions such a

sequencing, timing, counting and arithmetic in order to control machines and processes.


8/16/2019 15183.PLC (1)

9/33

Programmable logic controller• The term logic is used because programming is primarily concerned with implementing logic

switching operations, e.g. if A or B occurs switch on C, if A and B occurs switch on D.• Input devices, e.g. sensors , switches and output devices in the system being controlled, e.g.

motors, valves, etc., are connected to the PLC.• The operator then enters a sequence of instructions, i.e. a program, into the memory of the PLC

The controller then monitors the inputs and outputs according to this program and carries out thcontrol rules for which it has been programmed.


8/16/2019 15183.PLC (1)

10/33

Programmable logic controllerThey are designed to be operated by engineers with perhaps a limited knowledge of computers ancomputing languages. They are not designed so that only computer programmers can set up or

change the programs.Thus, the designers of the PLC have pre-programmed it so that the control program can be entereusing a simple, rather intuitive, form of language.


8/16/2019 15183.PLC (1)

11/33

PLC Applications• Previously hardwired arrays of relays were used to control the operation of heavy machines tha

contain motors and other high power devices.• PLCs were originally used to substitute the switching relay networks used in industrial

applications, but now they can also be used implement other tasks such as timing, delayingcounting, calculating, comparing and processing of analog signals.


8/16/2019 15183.PLC (1)

12/33

PLC v s Microcontroller• Programmable Logic Controller (PLC) defined by NEMA as a digitally operating electronic

apparatus that uses a programmable memory for internal storage of instructions for

implementing specific functions such as LOGIC, SEQUENCING, TIMING, COUNTING andARITHMETIC through digital or analog INPUT/OUTPUTMODULES.

Microcontroller is a microprocessor with internal input and output and memory i.e. RAM, ROM,PORTS.


8/16/2019 15183.PLC (1)

13/33

PLC v s MicrocontrollerGood things about PLC’s:• Its microprocessor based high end thoroughly developed Product for Industry which can be

programmed through high end programming software uses its different simple to understandLadder programming Language.

• PLC can be programmed to control anything from a power station to a small press. It has therequisite hardware and software to do this.

• PLC developed for Industrial Automation.• Development Time is less this seems to be cost effective solution in Service Industry.• Troubleshooting a PLC system is much more technician friendly and very easy to adapt and

change. Interfacing to a PLC is so much easier because it is designed for you basic machinesignals, DC/AC, A2D, High Speed Input, serial and networking. With a microcontroller, you mhave to design your own signal interfacing.

• PLC is a infinitely expandable input/output logic controller usually programmed with a externPC program


8/16/2019 15183.PLC (1)

14/33

PLC v s MicrocontrollerGood Things about Microcontroller• In case of Microcontroller the programming is some what tedious because of machine langua• A microcontroller is also a logic controller but used in dedicated systems which are programm

once and for all, the program for which will not be accessed by the user, and whose program wnot need to be altered frequently.

• Microcontrollers Developed for Dedicated equipment's.• Development Time is more.• With a microcontroller, you may have to design your

own signal interfacing. Microcontroller is not a infinitely

expandable input/output logic controller.


8/16/2019 15183.PLC (1)

15/33

PLC v s Computer


PLC Computer

Designed for extreme industrial environments Designed mainly for data processing and calculation

Can operate in high temperature and humidity. Optimized for speed

High immunity to noise. Can’t operate in extreme environments

Integrated command interpreter. Can be programmed in different languages

No secondary memory available (in the PLC). Lots of secondary memory available.

Optimized for Single task. Multitasking capability.

8/16/2019 15183.PLC (1)

16/33

PLC SizeManufacturers offer five sizes of PLCs:

1. Nano (up to 16 I/O points)

2. Micro (more than16 I/O points, up to 64 I/O points)

3. Small (up to 960 I/O points)

4. Medium (multitasking - control of several processes)

5. Large (control management of several PLCs)


8/16/2019 15183.PLC (1)

17/33

8/16/2019 15183.PLC (1)

18/33

Advantages of PLC• Increased Reliability• More Flexibility• Lower Cost• Faster Response• Easier to troubleshoot• Remote control capability• Communication Capability


8/16/2019 15183.PLC (1)

19/33

8/16/2019 15183.PLC (1)

20/33

PLC HardwareTypically a PLC system has the basic functional components of processor unit, memory, powersupply unit, input/output interface section, communications interface and the programming devic

Figure shows the basic arrangement.1. The processor unit or central processing unit (CPU)

2. The power supply unit.

3. The programming device.

4. The memory unit.

5. The input and output sections.

6. The communications interface


8/16/2019 15183.PLC (1)

21/33

PLC Hardware


8/16/2019 15183.PLC (1)

22/33

Internal architecture of PLC


8/16/2019 15183.PLC (1)

23/33

Internal architecture of PLC• Basic internal architecture of a PLC consists of a central processing unit (CPU)

system microprocessor, memory, and input/output circuitry.• The CPU controls and processes all the operations within the PLC. It is supplied with a clock w

frequency of typically between 1 and 8 MHz. This frequency determines the operating speethe PLC and provides the timing and synchronisation for all elements in the system.

• The information within the PLC is carried by means of digital signals . The internawhich digital signals flow are called buses . In the physical sense, a bus is just aconductors along which electrical signals can flow. It might be tracks on a printed circuit boawires in a ribbon cable.

• The CPU uses the data bus for sending data between the constituent elements, thesend the addresses of locations for accessing stored data and the control bus for sto internal control actions. The system bus is used for communications between the inpuports and the input/output unit.


8/16/2019 15183.PLC (1)

24/33

Internal architecture of PLCThe CPU: The internal structure of the CPU depends on the microprocessor concerned. In generthey have:

1. An arithmetic and logic unit (ALU) which is responsible for data manipulation and cout arithmetic operations of addition and subtraction and logic operations of AND, ORNOT and EXCLUSIVE-OR.

2. Memory, termed registers , located within the microprocessor and used to storeinformation involved in program execution.

3. A control unit which is used to control the timing of operations.


8/16/2019 15183.PLC (1)

25/33

Internal architecture of PLCThe buses• The buses are the paths used for communication within the PLC. The information is transmitte

binary form, i.e. as a group of bits with a bit being a binary digit of 1 or 0, i.e. on/off statesterm word is used for the group of bits constituting some information. Thus an 8-bit word mibe the binary number 00100110. Each of the bits is communicated simultaneously along its owparallel wire.

• The system has four buses:1. The data bus.2. The address bus.3. The control bus.4. The system bus.


8/16/2019 15183.PLC (1)

26/33

Internal architecture of PLCMemory: There are several memory elements in a PLC system:

1. System read-only-memory (ROM ) to give permanent storage for the operating sysfixed data used by the CPU.

2. Random-access memory ( RAM ) for the user’s program.3. Random-access memory ( RAM ) for data. This is where information is stored on t

of input and output devices and the values of timers and counters and other intedevices. The data RAM is sometimes referred to as a data table or registerthis memory, i.e. a block of addresses, will be set aside for input and output addresses

the states of those inputs and outputs. Part will be set aside for preset data and partstoring counter values, timer values, etc.4. Possibly, as a bolt-on extra module, erasable and programmable read-only

( EPROM ) for ROMs that can be programmed and then the program made permanent.


8/16/2019 15183.PLC (1)

27/33

Internal architecture of PLCInput/output unit:• The input/output unit provides the interface between the system and the outside world, allowin

for connections to be made through input/output channels to input devices such as sensors andoutput devices such as motors and solenoids. It is also through the input/output unit thatprograms are entered from a program panel. Every input/output point has a unique addresswhich can be used by the CPU.

• The input/output channels provide isolation and signal conditioning functions so that sensors aactuators can often be directly connected to them without the need for other circuitry


8/16/2019 15183.PLC (1)

28/33

Internal architecture of PLCPLC Input Devices:

1. Mechanical switches.

2. Proximity switches.

3. Photoelectric sensors and switches.

4. Encoders.

5. Temperature sensors.

6. Position/displacement sensors.

7. Strain gauges.8. Pressure sensors.

9. Liquid level detector.

10. Fluid flow measurement.

11. Smart sensors.


8/16/2019 15183.PLC (1)

29/33

Internal architecture of PLCPLC Output Devices:

1. Relay.

2. Directional control valves.

3. Motors.

4. Stepper motors.


8/16/2019 15183.PLC (1)

30/33

PLC ConfigurationsThere are two PLC basic configurations that commercial manufacturers offer.

1. Fixed Configuration.

2. Modular Configuration


8/16/2019 15183.PLC (1)

31/33

PLC ConfigurationsFixed Configuration:


8/16/2019 15183.PLC (1)

32/33

PLC ConfigurationsModular Configuration:


8/16/2019 15183.PLC (1)

33/33

PLC ApplicationsA PLC can be used in a wide range of applications, some of which are shown below:


Production and assembly lines

Automatic Doors Traffic Lights

15183.plc (1)

Documents