P L C General

PROGRAMMABLE LOGIC CONTROLLER

Control Systems Types  Programmable

Logic Controllers  Distributed Control System  PC- Based Controls

PLC  The

PLC is an assembly of solid state digital logic elements design to make logical decisions and provide outputs.  PLC is programmed interface between input sensor &output device.

Programmable Logic Controllers  Sequential

logic solver  PID Calculations.  Advanced Subroutines  BIT Operations.  Data Transfer.  Text Handling.

Programmable Logic Controllers Applications : 

Machine controls, Packaging, Material handling, similar Sequential task as well as Process control

Advantages of PLC : 

 



They are fast and designed for the rugged industrial environment. They are attractive on Cost-Per-Point Basis. These Devices are less Proprietary ( E.g.. Using Open Bus Interface.) These Systems are upgraded more Capabilities with dedicated PID and Ethernet Modules.

Disadvantages of PLC :  

PLC one time cost is high To maximize PLC performance a number of IO Modules to be

PLC Components(Hardware)      

Central Processing Unit (CPU) Input Modules Output Modules Power Supply Bus system Rack(Rail)

I/P mod

CPU

POWER SUPPLY

O/P mod

m

Central Processing Unit 



It is a micro-controller based circuitry. The CPU consists of following blocks : Arithmetic Logic Unit (ALU), Program memory Process image memory (Internal memory of CPU) Internal timers ,counters and Flags . CPU performs the task necessary to fulfill the PLC functions. i.e. Scanning I/O bus traffic control, Program execution, Peripheral and External device communication, data handling and self diagnostics.

Input module      

These modules act as interface between real-time status of process variable and the CPU. Analog input module : Typical input to these modules is 4-20 mA, 0-10 V Ex : Pressure, Flow, Level Tx, RTD (Ohm), Thermocouple (mV) Digital input module : Typical input to these modules is 24 V DC, 115 V AC, 230 V AC Ex. : Switches, Pushbuttons, Relays, pump valve on off status

Output module These modules act as link between the CPU and the output devices in the field.  Analog output module : Typical output from these modules is 4-20 mA, 0-10 V  Ex : Control Valve  Digital output module : Typical output from these modules is 24 V DC, 115 V AC, 230 V AC  Ex. : Solenoid Valves, lamps, Actuators, Pump valve on off control 

I/O MODULE SPECIFICATION        

COST INPUT VOLTAGE ON-STATE INPUT VOLTAGE RANGE AMBIENT TEMP RATING INPUT DELAY – NOMINAL OUTPUT VOLTAGE MAX O/P CURRENT ELECTRICAL ISOLATION –

Power Supply 

 

The power supply gives the voltage required for electronics module (I/O, CPU, memory unit) of the PLC from the line supply. The power supply provides isolation necessary to protect the solid state devices from most high voltage line spikes. As I/O is expanded, some PLC may require additional power supplies in order to maintain proper power levels.

Bus System  It

is path for the transmission of the signal between power supply module,processor and I/O modules.  The bus comprise of several single line i.e. wires /tracks

Advantage of PLC Over Relay RELAY

PLC

1-More wiring

1-Less wiring

2-Changes difficult

2-Changes easy

3-More power

3-Low power

4-More maintenance

4-Solid state reliability

5-Difficult to expand

5 -Easy to expand

PLC Cycle  Sense

the Input  Process the Logic  Give Output

Inputs

CPU

Outputs

PLC Signal Flow Input Module

Processor Memory

Output Modules

Data

I/p Image Table

I:0/6

I:0/6

Output Image Table

O:0/7 O:0/7

I:1/4

O:1/5

Input Devices Ladder Program

I:1/4

I:0/6

O:0/7

I:1/4

O:1/5

Programming Terminal

Output Device

O:1/5

PLC Architecture Evolution ◆

1970s : Discrete Machine Control Programming Terminal Connection is Point to Point

PLC Connection is Point to Point

I/O

Programming Language : - Relay ladder logic - Flexibility in altering Control system

PLC Architecture Evolution ◆

1985 : Discrete and Process Control Reasonable Computer Running PLC Programming Software

MS - DOS

PLC Programming Language :

I/O

- Ladder Program - PID - Data Storage

PLC Architecture Evolution ◆

1990’s : Discrete and Process Control Windows

PC running PLC Programming Software Connection in networked allowing Multiple PLC

PLC

I/O

PLC PLC became a part of the developing enterprise resource system

PLC Architecture Evolution

Today : Distributed I/O Modules PL C

Distributed I/O scanner

Data Communication Bus

Distributed I/O modules

PLC Architecture Evolution Today : Hot Redundant System

SPLITTERS Remote I/O Network FIBER OPTIC LINK

Remote I/O

PLC Architecture Evolution Today : Ethernet Technology in PLCs

Workstation

Workstation

Workstation

Workstation

Switched Hub

Controller Controller Controller

Controller

PLC Architecture Evolution Today : Wireless communication PLC Wireless Modem

Remote Platform Wireless Modem PLC

HMI Display

PC

PLC Systems of various vendors Siemens  

S5 -110U, 115U, 135U S7 - 200, 300, 400

Allen Bradley 

 

Micrologix 1000, 1200, 1500 SLC 5/01, 5/02, 5/03 LOGIX PLATFORM

Modicon    

Nano Micro Premium Quantum

Configuration of PLC : Modicon Built in display for I/O (in-rack, AS-i) and Diag

Programming Terminal PC Connection

8 Analog Inputs 1 Analog Output

I/O Modules

Up/Down Fast Counter

Up Counter Unitelway Port for connection of up to 5 Slaves

TSX37-22 PCMCIA communications port PCMCIA memory expansion port

Configuration of PLC : Siemens

CPU I/O Modules External Power Supply

Configuration of PLC : Allen Bradley

CPU I/O Modules Power Supply

Configuration of PLC : GE FANUC I/O Modules

CPU

Back plane

PLC Programming Standards

   

Ladder Diagram Function Block Diagram Sequential Function Chart Structured Text Language

Scan Rate 

The completion of one cycle of the sequence is called- SCAN



Time required for one cycle is called SCAN TIME

PLC Selection Criteria        

Cost of hardware, I/O requirement CPU memory Spare parts& Maintenance, Reliability, Flexibility& Integration of High-level Application. Compatible Protocol

Memory Types      

ROM (Read Only Memory) RAM (Random Access Memory) PROM (Programmable ROM) EPROM (Erasable PROM) EAROM- Electrically alterable ROM EEPROM-Electrically erasable PROM

Binary System ◆

◆ ◆ ◆

BIT – Each digit of a binary number i.e.0 or1 BYTE – Group of 8 bits WORD = Two bytes=16 bits DOUBLE WORD =Two word 7 6 5 4 3 2 1 0 =4bytes=32bits 8 BIT WORD

BYTE

BYTE 16 BIT WORD

PLC : Terminology ◆ ◆ ◆ ◆ ◆

INPUT is referred by – I OUTPUT is referred by – Q or O TIMER is referred by – T FLAGS are referred by – M or B COUNTERS are referred by – C

PLC : Protocol ◆

◆ ◆ ◆ ◆ ◆ ◆ ◆

It is a set of rules for data transmission when PLC is connected to network RS-232 (Recommended standard) RS-485 MPI(Multi point Interface) Profibus DH(Data Highway) Ethernate Controlnet