PLC General

PROGRAMMABLE LOGIC

CONTROLLER

Prolific Systems and Technologies Pvt Ltd

Early control systems consisted of huge control boards consisting of hundreds to thousands of electromechanical relays.

An engineer would design the system logic, electricians would receive a schematic outline of logic then implement the logic with relays.

The schematic was commonly called “Ladder Schematic” The ladder displayed all switches, sensors, motors, valves,

relays etc in the system. Problems: Long commissioning time, dependency on

mechanical reliance, Any system logic design change required the power to the control board to be isolated stopping production.

History History


General Motors was among the first to recognize a need to replace the systems “wired control board”

Hydramatic Division of GM specified the design criteria for the programmable controller in 1968.

Goal – Eliminate the high cost associated with inflexible, relay controlled systems.

History History


New Controller Specifications: Solid State System Computer Flexibility Operate in Industrial Environment (vibrations, heat, dust

etc.) Capability of being reprogrammed Easily programmed and maintained by electricians and

technicians.

History History


In 1969 Gould Modicon developed the first PLC. Strength – Programmed with Ladder Logic Initially called Programmable Controllers PC’s

Now - PLC’s, Programmable Logic Controllers PLC’s have evolved from simple on/off control to being

able to communicate with other control systems, provide production reports, schedule production, diagnose machine and process faults.

History History


Advantage of PLC Over Relay Advantage of PLC Over Relay StyleStyle

RELAY PLC

1-Hard wiring 1-Less wiring

2-Changes difficult 2-Easy modification

3-More power 3-Low power

4-More maintenance 4-Less maintenance

5-Difficult to expand 5-Ease of expansion


Control Systems TypesControl Systems Types

Programmable Logic Controllers Distributed Control System PC- Based Controls


NEMA Definition year 1978NEMA Definition year 1978National Electrical Manufacturers AssociationNational Electrical Manufacturers Association

The PLC, also known as programmable controller is defined by the National Electrical Manufacturers Association (NEMA) in 1978 as:

"a digitally operating electronic apparatus which uses a

programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequencing, timing, counting and arithmetic, to control through digital or analog input/output, various types of machines or process".


Applications : Machine controls, Packaging, Palletizing, Material handling,

similar Sequential task as well as Process controlAdvantages 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 to add more Intelligence and

Capabilities with dedicated PID and Ethernet Modules.Disadvantages of PLC : PLC were Designed for Relay Logic Ladder and have Difficulty

with some Smart Devices. To maximize PLC performance and Flexibility, a number of

Optional Modules must be added PLC holds only one copy of program

Programmable Logic Programmable Logic Controllers Controllers

PLC Types Nano (Small) Micro (Medium) Large

Basic criteria for PLC Types Memory Capacity I/O Range Packaging and Cost per Point

Programmable Logic Programmable Logic Controllers Controllers


Sizing of PLCSizing of PLC

Micro PLCs: I/O up to 32 points Small PLC: I/O up to 128 points Medium PLC: I/O up to 1024 points Large PLC: I/O up to 4096 points Very Large: I/O 4096 Onwards


Most Basic of PLC Most Basic of PLC SystemsSystems

In the most basic of PLC systems, a self contained (shoe box) PLC has 2 terminal blocks, one for Inputs and one for Outputs

Today, most PLC’s in this category are know as Micros. Typically they provide front panel LED status indication of I/O and Processor states

InputsOutputs

CR


Modular Chassis Based PLC’sModular Chassis Based PLC’s

The vast majority of PLC’s installed today are modular chassis based systems consisting of:

1. Processor Module (CPU)2. Input & Output Modules3. Chassis4. Power Supply


Modular Chassis-less PLC Modular Chassis-less PLC SystemsSystems

Also available from many vendors are “Chassis less” but still Modular PLC systems. These systems still require a Processor, I/O Modules, and Power Supply, but in place of a chassis these components mount directly onto a panel, din rail, and many use a tongue and grove system to allow easy insertion and removal


Central Processing Unit (CPU) Input Output Modules Power Supply Bus system Programming Device

P L C Components P L C Components

CPU

PROGRAMDEVICE

IN OUT m

MODULEMODULE


Basic PLC SchematicBasic PLC Schematic

CPU Power Supply Memory Input Blocks Output Blocks Communications Expansion

Connections


It is a micro-controller based circuitary. The CPU consists of following blocks :

Arithmatic Logic Unit (ALU), Timing / Control ckt, Program memory, Process image memory (Internal memory of CPU)

Internal timers and counters and Flags, Address stack and instruction registers

The Central Processing Unit (CPU) Module is the brain of the PLC.

P L C : Central Processing P L C : Central Processing Unit Unit


CPU ModuleCPU Module

CPU performs the task necessary to fulfill the PLC functions. These tasks include Scanning, I/O bus traffic control, Program execution, Peripheral and External device communication, special functions or data handling execution and self diagnostics.

SelfCheck

ExecuteCode

ScanInputs

UpdateOutputs

PLC ProgramSCAN

Primary role to read inputs, execute the control program, update outputs.


MemoryMemory

The memory includes pre-programmed ROM memory containing the PLC’s operating system, driver programs and application programs and the RAM memory.

PLC manufacturer offer various types of retentive memory to save user-programs and data while power is removed, so that the PLC can resume execution of the user-written control program as soon as power is restored.


MemoryMemory

Many PLCs also offer removable memory modules, which are plugged into the CPU module.

Memory can be classified into two basic categories: volatile and non-volatile.

Volatile memory loses state (the stored information) when power is removed.

Nonvolatile memory, maintains the information in memory even if the power is interrupted.


MemoryMemory

Some types of memory used in a PLC include: ROM (Read-Only Memory) RAM (Random Access Memory) PROM (Programmable Read-Only Memory) EPROM (Erasable Programmable Read-Only Memory) EEPROM (Electronically Erasable Programmable Read-Only

Memory) FLASH Memory Compact Flash – Can store complete program information,

read & write text files


I/O ModulesI/O Modules

Input and output (I/O) modules connect the PLC to sensors and actuators.

Provide isolation for the low-voltage, low-current signals that the PLC uses internally from the higher-power electrical circuits required by most sensors and actuators.

Wide range of I/O modules available including: digital (logical) I/O modules and Analog (continuous) I/O modules.


These modules act as link between field input sensors and the CPU.

Analog input module : Typical input to these modules is 4-20 mA, 0-10 V, Ohms, mV

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

PLC : Input module PLC : Input module



Transfer of data:-I/P sensor to CPU Conversion:- 24vdc/230vac to 5vdc Isolation :- By Opto Coupler


Input DevicesInput Devices

Pushbuttons Selector Switches Limit Switches Level Switches Photoelectric Sensors Proximity Sensors Motor Starter Contacts Relay Contacts Thumbwheel Switches


Digital Inputs ModulesDigital Inputs Modules

The list below shows typical ranges for input voltages. 5 Vdc – used when Microcontroller based sensors are used as I/P 12 Vdc Now not much used 24 Vdc – Widely used (Standard for I/P) 48 Vdc - Was used high power devices pneumatic / hydraulic cylendors / limit switches 12 Vac not being used 24 Vac discontinued 120 Vac Sensors are at long distance from controller 240 Vac – Not much used


SOURCING vs. SINKING DC SOURCING vs. SINKING DC InputsInputs

DC Power Supply

Field Device

DC Input Module

+

- DC COM

IN1

C

DC Input Module

Field Device

DC Power Supply

+

-

+VDC

IN1

IN1VDC

SINK SOURCE


Analogue Inputs/OutputsAnalogue Inputs/Outputs

Analogue input cards convert continuous signals via a A/D converter into discrete values for the PLC

Analogue output cards convert digital values in then PLC to continuous signals via a D/A converter.

Resolution can be important in choosing an applicable card Example, for a temperature input of 0 to 100 degrees C

For 8 bit resolution the value in the PLC is 0 to 255 For 12 bit resolution the value in the PLC is 0 to 4095 For 12.5 bit resolution the value in the PLC is 0 to 6000 For 13 bit resolution the value in the PLC is 0 to 8192 For 16 bit resolution the value in the PLC is 0 to 32768


Analogue CardsAnalogue Cards

Typical Analogue Input signals are: Flow sensors Humidity sensors Load Cells Potentiometers Pressure sensors Temperature sensors Vibration

Analogue Output signals control: Analogue Valves Actuators Chart Recorders Variable Speed Drives Analogue Meters

Typical Analogue Signal Levels 4-20mA 1-5 Vdc 0-10 Vdc -10 – 10VdcProlific Systems and Technologies Pvt Ltd

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, Speed, Vibration Digital output module : Typical output from these modules is

24 V DC, 115 V AC, 230 V AC Ex. : Solenoid Valves, lamps, Actuators, dampers, Pump

valve on off control

PLC : Output module PLC : Output module


Relay type -For AC or DC

Transistor Type Logic(TTL) - For DC Triac (Triode AC) type - For AC Isolated common type -For

different device

PLC : Output module - Types PLC : Output module - Types


PLC : Output module PLC : Output module


Output DevicesOutput Devices

Valves Motor Starters Solenoids Control Relays Alarms Lights Fans Horns

Relays 120 VAC/VDC 240 VAC 24 VAC/VDC

Triac 120/230 VAC

Transistor MOSFET 24 VDC


RelaysRelays

The most important consideration when selecting relays, or relay outputs on a PLC, is the rated current and voltage.

For transistor outputs or higher density output cards relay terminal blocks are available. Advantage of individual standard replaceable relays


I/O SpecificationsI/O Specifications

INPUT VOLTAGE – Magnitude and type of voltage ON-STATE INPUT VOLTAGE RANGE – voltage at which signal is

recognized Nominal current per input – Min. current to operate input circuit AMBIENT TEMP RATING – Max temp of surrounding the I/O

module INPUT DELAY – Time duration for input signal to be on before

known as valid input. ( 9-ms to 25ms) NOMINAL OUTPUT VOLTAGE – It is min and max o/p operating

voltage.e.g. Rated 120 v ac o/p ckt. Works in 92 to 138 v range. MAX O/P CURRENT RATING – Max current a single o/p or

module can safely carry under load OFF –STATELEAK CURRENT PER O/P – Max value of leak current

flows through the o/p in OFF position ELECTRICAL ISOLATION – Max volts between I/o and logic ckt.


The power supply gives the voltage required for electronics module (I/O Logic signals, CPU, memory unit and peripheral devices) 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.

P L C : Power P L C : Power Supply Supply


It is path for the transmission of the signal . Bus system is responsible for the signal exchange between processor and I/O modules

The bus system comprise of several single line ie wires / tracks

Types of Bus

P L C : Bus System P L C : Bus System

Address bus - Location Data bus - Carries Data Control bus - Synchronization


Special ModulesSpecial Modules

RF ID Voice Gas Flow Calculation Weigh Cell Hydraulic Servo ASCII Fuzzy Logic Temperature Sensor Temperature Control Heat/Cool Control Field Bus Cards

DeviceNet, Profibus etc Lonworks, BACNet

Fast Response (Interrupt) PID Loop Controller BASIC Cards RS232 Comm’s Modbus ASCII/RTU Ethernet Comm’s High Speed Counters Position Control Cards Peer to Peer Comm’s

Controller Link DH+ Modbus Plus


Input Scan

Program ScanOutput Scan

Housekeeping

START

Each ladder rung is scanned using the data in the Input file. The resulting status (Logic being solved) is written to the Output file (“Output Image”).

The status of external inputs (terminal block voltage) is written to the Input image (“Input file”).

The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF.

Internal checks on memory, speed and operation. Service any communication requests, etc.

PLC Operating CyclePLC Operating Cycle

This scan cycle can be interrupted if required using interrupts


PLC Signal FlowPLC Signal Flow

Programming Terminal

O:0/7

O:0/7

O:1/5

Output Devices

Output ModulesProcessor MemoryInput Module

Input DevicesLadder 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 InputImage Table

OutputImage Table

PLC Architecture EvolutionPLC Architecture Evolution Mid - 1970s : Discrete Machine Control

ProgrammingTerminal

PLC

I/O

Programming Language :

- Relay ladder logic - Flexibility in altering Control system operation

Connection is Point to Point


Early - to - Mid 1980 : Discrete and Process Control

PLC Architecture EvolutionPLC Architecture Evolution

Reasonable ComputerRunning PLC

Programming Software

PLC

I/O

Programming Language :

- Ladder Program - PID - Data Storage

MS - DOS


PLC Architecture EvolutionPLC Architecture Evolution

Late 1980’s to early 1990’s : Discrete and Process Control

PC running PLC Programming Software

PLC

I/O

Connection in networked allowing Multiple PLC

PLC became a part of the developing enterprise resource system

Windows

PLC


TodayToday : : Distributed I/O ModulesDistributed I/O Modules

Distributed I/O modules

PLC

Distributed I/O scanner

Data Communication Bus

PLC Architecture PLC Architecture EvolutionEvolution


Remote I/O Network

SPLITTERS

FIBER OPTIC LINK

TAPS

Remote I/O

Today : Today : Hot Redundant SystemHot Redundant System


Level of redundancyLevel of redundancyPower SupplyPower Supply

CPUCPUI/OI/O

CommunicationCommunication


Controller ControllerController

Controller

Workstation Workstation Workstation Workstation

Switched Hub

PLC Architecture PLC Architecture EvolutionEvolutionToday : Today : Ethernet Technology in PLCsEthernet Technology in PLCs


RemotePlatform

Wireless Modem / GSM Communication

Wireless Modem / GSM Communication

PLC

H M I Display

PC


Today : Today : Wireless communicationWireless communication

PLC


8 Analog Inputs 1 Analog Output

Up/Down Fast Counter

Up Counter

Programming Terminal PC Connection

Unitelway Port for connection of up to 5 Slaves

PCMCIA memory expansion port

PCMCIA communications port

TSX37-22

Built in display for I/O (in-rack, AS-i) and Diag

I/O Modules

Configuration of PLC : Configuration of PLC : ModiconModicon


Configuration of PLC : Configuration of PLC : SiemensSiemens

CPU

External Power Supply

I/O Modules


Configuration of PLC : Allen Configuration of PLC : Allen BradleyBradley

CPU

Power Supply I/O Modules


Configuration of PLC : GE FANUCConfiguration of PLC : GE FANUC

CPU

I/O Modules Back plane


PLC Programming StandardsPLC Programming Standards

The open, manufacturer-independent programming standard for automation is IEC 61131-3. You can thus choose what configuration interface you wish to use when writing your application :

Ladder Diagram Statement List Instruction List Function Block Diagram Sequential Function Chart Structured Text


Scan RateScan Rate

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

Time required for one cycle is called SCAN TIME


Binary System Binary System

BIT – Each digit of a binary number BYTE – Group of 8 bit WORD – Group of one or more byte LSB – Least significant bit or

smallest value MSB – Most significant bit or largest

value

1 0234567

8 BIT ( 1 BYTE )LSBMSB

BYTE BYTE16 BIT (1 WORD)


PLC : PLC : Terminology Terminology

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


PLC : Communication Protocol PLC : Communication 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) Ethernet Controlnet Devicenet


Baud rate (Communication Speed)Baud rate (Communication Speed)

It is rate of data transmission on network Unit is bits/second

Range:- 120 bits /sec to 100 Mega bits per second


Selecting a PLCSelecting a PLC

Number of logical inputs and outputs Memory Number of special I/O modules Expansion Capabilities Scan Time Communication Software Support Cost


Manufactures – Major BrandsManufactures – Major Brands

OMRON Allen Bradley Schneider GE Fanuc Siemens Automation Direct (Koyo) Toshiba Mitsubishi Hitachi Keyence VIPA


PLC StandardizationPLC Standardization

IEC 61131 Based on IEC 1131 (1992) standard, developed to be

a common and open framework for PLC architecture. IEC 61131-1 Overview IEC 61131-2 Requirements & Test Procedures IEC 61131-3 Data Types & Programming IEC 61131-4 User Guidelines IEC 61131-5 Communications IEC 61131-7 Fuzzy Control IEC 61131-7 Guidelines for the application and

implementation of programming languages


PLC PLC ProgrammingProgramming

The purpose of a PLC Program is to control the state of PLC outputs based on the current condition of PLC Inputs

Different PLC’s support different languages, but the most popular PLC language is know as “Ladder Logic”.

PLC Ladder Logic purposely resembles Relay Logic


IEC 61131-3IEC 61131-3

IL (Instruction List) – mnemonic programming LD (Ladder Diagram) – Relay logic ST (Structured Text) – A BASIC like programming language FDB (Functional Block Diagram) – Graphical dataflow

programming language SFC (Sequential Flow Chart) – Graphical method for

structured programs


| | |/|

Read / Conditional Instructions

Write / Control Instructions

| | |/|

| | |/|

| |

| | |/| ( )

| |

( )

( )

( )

( )

| |

Start (Rung #1)

End (Rung #5)

Ladder Logic Concepts Ladder Logic Concepts


Read / Conditional Instructions

Write / Control Instructions

No Logical Continuity

|/| | |

True False False

|/| |/|

( )

( )

True True True

Logical Continuity


Ladder Logic Concepts Ladder Logic Concepts

IF input 4 AND input 5 have powerTHEN energize output 0

| |I/4

| |I/5

( )O/0

Logical ContinuityT T T

On


Logical AND Logical AND Construction Construction

|/|I/11

| |I/5

|/|I/7

|/|I/1

| |I/3

| |I/2

| |I/4

|/|I/0

| |I/1

| |I/1

|/|I/8

| |I/9

( )O/0

| |I/10


Typical Construction Typical Construction

L1 L2

PB1 LS1 PS2 SOL6

DEVICE

PB1

LS1

PS2

SOL6

| | ( )| | | |I/5 I/6 O/0I/7

HHPI/5

I/6

I/7

O/0

LogixI:0/5

I:0/6

I:0/7

O:0/0

ADDRESS


Addressing ExamplesAddressing Examples

INPUT Address Assignment:PB1- I/4 PB2- I/5LS1- I/6 LS2- I/7LS3- I/8 LS4- I/9

OUTPUT Address Assignment:SOL2- O/0 M1- O/1

|/|

CR3

CR3 M1

PB1 LS1 SOL2

PB2LS1

LS3

LS4

I/8

I/4 I/6 O/0

O/1

| | | | ( )

I/5I/7 B/0| | | | ( )

| |

|/|B/0

( )

Relay Logic to Ladder LogicRelay Logic to Ladder Logic

| |I/9


Available InstructionsAvailable Instructions

Sequence Input Output Control

Logic Timer and Counters Comparison Range Comparison Data Movement Data Shift Step / Step Next Serial Communications Text String Processing File Manipulation

Increment/Decrement Conversion

ASCII Number Systems

Math Floating Point Math Statistics Scaling PID PID with Auto tune Clock / Date Block Processing

IF,THEN,ELSE,LOOPTable Processing

LIFO, FIFOProlific Systems and Technologies Pvt Ltd

Few more InstructionsFew more Instructions

SEQUENCERS

SHIFT REGISTERS

DATA HANDLING

HIGH SPEED COUNTER

SUBROUTINES


Thanks Thanks ….….


PLC General

Engineering

Transcript of PLC General