Intro to PLC 0135044660

PLC

by ; aidi sulaiman PJB 2004 1

1. AUTOMATIC CONTROL

Automatic control is an operation of electronic devices or apparatus that take place the

jobs of human operator.

HUMAN

OBSERVATION

(INPUT)

JUDGEMENT

(BRAIN)

DECISION

(OUTPUT)

AUTOMATIC

CONTROL

SENSING

(SENSOR)

CONTROLLING

(PROCESSOR)

OUTPUT

(ACTUATOR)

2. COMPOSITION OF SEQUENTIAL/AUTOMATIC CONTROL SYSTEMS

INP

UT

SENSING CONTROLLING ACTUATING

OU

TPU

T

SENSOR

MICRO SWITCH

LIMIT SWITCH

PUSH BOTTON

SWITCH

REED SWITCH

PROXIMITY SWITCH

PHOTOELECTRIC

SWITCH

SENSOR

ETC

HARD WIRE

(CONVENTIONAL SYSTEM)

RELAY

TIMER

COUNTER

CONTACTOR

ELECTRONIC LOGIC

PNEUMATIC LOGIC

HYDRAULIC LOGIC

ELECTRO-PNEUMATIC

LOGIC

ELECTRO-HYDRAULIC

LOGIC

ACTUATOR

MOTOR

SOLENOID VALVE

LAMP

BUZZER

ETC

PROGRAMMABLE LOGIC

CONTROLLER (PLC)

PLC


INPUT DEVICES

OUTPUT DEVICES

PLC


WHAT IS PLC?

PLC Defination

A digitally operated 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 modules, various types of machines or processes.- National Electrical Manufacturers Association (NEMA)

In conventional/hard-wired systems we use relays as a main device to do

sequential/automatic control. A PLC is a kind of micro computer which we compose

programs by typing without wiring. Wiring only been done at input and output devices .

PLCs provide ease and flexibility of control using software and executing simple logic

instructions (ladder diagram). PLCs have internal functions such as timers, counters and

relays.

A PLC operates by reading the input signals (sensors) from process and carrying

out logic instructions (ladder programming) on these inputs signals, producing output

signal to drive output actuators. Standard interfaces built in to the PLCs allow them to be

directly connected to process sensors and actuators without the need for intermediate

circuitry or relays.

Through the use of PLCs became possible to modify a control system without

having to disconnect or re-direct a single wire. Its only necessary to change the control

program(software) using a programming console, visual display unit or PC. PLCs also

require much shorter installation and commissioning times than hard wired control

systems.

HISTORICAL BACKGROUND

In 1968, a group of engineers from General Motors developed the concept of PLC with

an initial specification. The PLC must be:

i. Easy to program and reprogram.

ii. Easy to maintain and repair.

iii. More relible in an industrial environment

iv. Smaller in size than its relay equivalent

v. Cost competitive

Before the 1980s, programmable logic controllers were called PCs.

PLC


COMPARISON BETWEEN PLC AND CONVENTIONAL SYSTEMS.

A PLC performs the functions of conventional relays, timers, counters. The Advantages

(over conventional devices hardwire)

i. Can be used for complex controlling.

ii. Fast operating speed

iii. Easy installation

iv. Very compact (Less space, more compact)

v. Flexible in control changes (More flexibility)

vi. Simple maintenance

vii. Higher reliability (less mechanical parts)

viii. Modular (Easily connected to computer systems and to hardware)

M1

+V

V112V

RL1

12V

PB1

STARTPB2

STOP

RL1

NO1

NO2

RL1

PB2STOP

+24V

MOTOR

PB1START+24V

CPM1A20CDR

i/p 2

i/p 3

i/p 4

i/p 5

i/p 6

i/p 7

i/p 8

i/p 9

i/p 10

i/p 11

i/p 0

i/p 1

COM

o/p 0

o/p 1

o/p 2

o/p 3

o/p 4

o/p 5

o/p 6

o/p 7

o/p 8

COM

U1

PLC


Control Function.

PLC can perform various functions such as:

1) Sequential Control.

a. Logic Control/function (AND, OR, AND NOT, OR NOT)

b. Timer/Counter.

c. etc

2) Arithmetic/Advance Control.

a. Mathematical function (+-*/)

b. P,I,D

c. Temperature

d. Servo motor speed

e. Etc

3) Supervisory Control

a. SCADA

b. LAN

c. WIFI

d. etc

TYPES OF PLC.

PLC types are based on their size and features. The PLC size and feature are depends on

manufacturer specification. They can be programed by using FIT, programming console

and PC. they can be placed into :

a. Pico or Nano,

b. Micro or Mini

c. Modular or Rack

d. Etc such as RTU (Remote Terminal Unit) SCADA , PAC (programmable automation

controllers) and DCS (distributed control system) (New Technology & Very

Advance Features).

** (The most known are a, b and c)

PLC


PICO or NANO PLC.

Smallest PLC in the world. Programming can be done on the PLC itself or by PC. The

function are based on their features. Example Allan Bradely PICO, OMRON Zen &

Siemens LOGO

MICRO OR MINI PLC.

Smaller size and highly integrated for a discrete and analog application in controls.

Almost every industry used it. Programming can be done by PC or Programming Console.

The function are based on their features. Example OMRON CP, Mitsubishi FX and Siemens

S5 Sieries.

PLC


MODULAR OR RACK PLC.

Interchangeable modules and highly integrated for a discrete and analog application in

controls. Can be expanded flexibly at any time via pluggable I/O, functional and

communications modules, providing tailored solutions for our requirements. A wide range

of performance, scope and interface options depending on our application. It have

most advance features used in DCS and SCADA. Programming can be done by PC, FIT

and HMI. Example OMRON CJ & Siemens S7 Sieries.

PLC


PLC MANUFACTURERS.

i. OMRON

ii. KEYENCE

iii. ALLAN BRADLEY

iv. GE

v. MITSUBISHI

vi. FUJI

vii. SIEMENS

viii. FESTO

ix. MICROLOGIC

x. Etc.

Why PLCs used in Industries ?

Advantages

+ many inputs and outputs, excellent for controlling and monitoring many processes

+ designed for industrial environments, robust and reliable

+ reprogrammable

+ modular

+ ideally suited to supervisory control (SCADA- Supervisory Control And data Acquisition)

+ easy to set up & maintenance, good for FMS(Flexible Manufacturing Systems)

+ inexpensive

+ predictible cost

+ high realibility (low maintenance)

+ standards i/o parts

Disadvantages

- do not use the full capabilities of the microprocessor

- ladder logic programming style is cumbersome and prone to mistakes

- only good for yes/no decisions

- do not handle continuous inputs and outputs, not good for direct control

- inflexible (compared to microprocessors)

PLC


PLC HARDWARE (BLOCK)

Power

Supply

Programming

Unit/VDU/PC/HMI/GUI

Programming Console

Signals

from

switches,

sensors,

etc

Input

interface

Central processing

unit (CPU)

Output

interface

Signals to

actuators,

solenoids,

motor,

etc Memory

PLCs are similar to computers which also consists of three functional areas :

processing, memory and input/output. Input signals to the PLC are read and then stored

in memory, where the processor performs the programmed logic instructions on these

input signals. Output signals are then generated to drive output devices. The action

taken depends totally on the program which is stored in the memory. In addition a

programming unit is used to download the programs to the PLC memory.

CENTRAL PROCESSING UNIT(CPU)

The CPU control, monitors and supervises all operations within the PLC. It also carries out

programmed instructions stored in the memory. An internal communications highway

also know as a bus systems, carries information to and from the CPU, memory and I/O

units, under the control of the CPU.

MEMORY SECTION

The memory section is where the program sequence is stored. There are two group of

memory.

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i. Volatile memories - Data which lose their contents when power OFF

ii. Non-volatile memories- Data that retain contents when power OFF

Volatile memories

RAM(Random Access Memory) allows individuals signals or data words to be written in or

read out when correct control signals are present. A battery backup is required to

preserved the contents in event of power interruption.

Non-volatile memories

This group can be devided into erasable and non-erasable memories.

i. Non erasable memory

ROM(Read only memory) which is permanently programmed at

manufacture and cannot be altered.

PROM(Programmable ROM) can be programmed by the user using a

PROM programmer.

ii. Erasable memory

EPROM (Erasable PROM) are programmed in a similar way to PROMs. Their

contents can be erased by exposure to ultra violet light. It can be re-

programmed over and over again.

EEPROM(Electrically EPROM) are similar to EPROM but can be erased

electrically while connected in the circuit.

PLC


Input/Output interface

The I/O units form the interface between the internal microelectronics of the PLC and the

outside world. It must there fore provide all necessary signal conditioning isolation

functions (opto isolator). This often allows a PLC to be directly connected to process

inputs apparatus and actuators without the need for intermediate circuitry or relays.

PLC


PLC INPUT WIRING

PLC


PLC WIRING FOR TRANSISTOR OUTPUT TYPE

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PLC WIRING FOR RELAY OUTPUT TYPE

PROGRAMMING UNITS

There are several types of programming units that can be use to program, monitor and

force the plc :

i. Hand held programming console

ii. Visual display unit (VDU)

iii. Factory intelligent terminal (FIT)

iv. Personal Computer (PC)

Programming Console

PLC


POWER SUPPLY

The power supply is depends on its specifications :

i. AC Voltage 100 to 240V

ii. DC Voltage 24V

SEQUENTIAL LOGIC UNDERSTANDING

i. Knowledge of parts

Constructions

Characteristics

Specifications

Functions

Applications

Selections

ii. Knowledge of circuits

Review

Analyze

Draw

iii. Creative designing

New idea by technical and engineering revolution

PLC PROGRAMMING AND WIRING.

There are 4 steps that usually been used in designing using PLC :

i. List of Input/output assignment

ii. Input/output wiring drawing

iii. Ladder diagrams explanation

iv. Logic instructions (mnemonic code/statement list)

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Input/output assignment

Input device Name Input No

Push Button 1 PB1 0000 / X00

Push Button 2 PB2 0001/ X01

Output device Name Output No

Lamp L1 1000 / Y00

Input/output wiring

There are many types of wiring for input and output devices. Its depends on the

specifications on PLCs.

i) Input Wiring.

a) DC inputs with common supply/source.

b) DC inputs with common ground/sink.

c) AC inputs.

ii) Output wiring.

a) Relay outputs with common supply.

b) Relay outputs with common ground.

c) Transistor outputs with common supply.

d) Transistor outputs with common ground.

PLC I/O WIring

PLC


Ladder diagrams explanation

Ladder Diagram

Logic instructions (mnemonic code)

Address Instructions Operand

0000 LD 0000

0001 OR 1000

0002 AND NOT 0001

0003 OUT 1000

0004 FUN(01)

Mnemonic Code

LOGIC INSTRUCTIONS(MNEMONIC) AND PROGRAMMING

Logic instructions are used as the basic programming language for PLCs.

Although logic instructions are easy to earn and use, it can very time consuming to

check and relate a large coded program to the actual circuit function. Furthermore

logic instructions tend to vary between different types of PLC. A factory plant may used

PLC


a range of different PLC, in which confusion can result over differences in the instruction

sets.

Another alternative is to use graphic programmer such VDU and PC. It enables

the user to enter his program as a ladder circuit layout using standard logic symbols to

represents inputs contacts, output coils and etc. This approach is more user friendly than

using mnemonic programming.

MNEMONIC/Name SYMBOL/KEY INPUTS Descriptions

LD

Load

LD 000.00

OUT 010.00

Creates a Normally Open condition

as the first conditions of the bus bar.

All instruction lines begin with either

LOAD or LOAD NOT

LD NOT

Load Not

LD NOT 000.00

OUT 010.00

Creates a Normally Closed

condition as the first conditions of

the bus bar. All instruction lines begin

with either LOAD or LOAD NOT

AND

And

LD 000.00

AND 000.01

OUT 010.00

Combines a normally open

conditions in series with a previous

conditions

AND NOT

And Not

LD 000.00

AND NOT 000.01

OUT 010.00

Combines a normally closed

conditions in series with a previous

conditions

OR

Or

Combines a normally open

conditions in parallel with a previous

conditions

PLC


LD 000.00

OR 000.01

OUT 010.00

OR NOT

Or Not

LD 000.00

OR NOT 000.01

OUT 010.00

Combines a normally closed

conditions in parallel with a previous

conditions

AND LD

And Load

LD 000.00

OR 000.02

LD 000.01

OR 000.03

AND LD

OUT 010.00

Combines two groups conditions in

series. These groups are called

blocks.

OR LD

Or Load

LD 000.00

AND 000.01

LD 000.02

AND 000.03

OR LD

OUT 010.00

Combines two groups conditions in

parallel. These groups are called

blocks.

OUT

Output

Specifies an output bit is to be turn

ON for an ON execution condition

PLC


LD 000.00

OUT 010.00

and OFF for an OFF condition.

OUT NOT

Out Not

LD 000.00

OUT NOT 010.00

Specifies an output bit is to be turn

OFF for an ON execution condition

and ON for an OFF condition.

TIM

Timer

LD 000.00

TIM 001 #0030

Creates a 0.1s decrementing timer

that stsrts from the set value (SV)

when the execution conditions turns

ON.

CNT

Counter

LD 000.00

LD 000.01

CNT 001 #0010

Counts down the number of times

the input condition turns ON. Each

time the input condition turns ON,

the present values(PV) is reduced by

1 and when the count reaches 0,

the completion flag turns ON.

END(01)

End

Indicates the end of the program. A

program will not be executed unless

the END instruction is used

PLC


KEEP(11)

Keep

LD 000.00

LD 000.01

KEEP HR10.00

Latches bit ststus. The bit is set when

the input (I) turns on and stsys set

until the reset (R) turns ON. The

function are same as SELF HOLDING

STANDARD AND SPECIAL FUNCTIONS IN PLC

Standards and special functions in PLC are not actual physical inputs and outputs. They

are used within the controller which are call internal bits. Certain number ranges(bits)

signed to each block of functions. This number range will depend both on the size of the

PLC and manufacturer.

STANDARD/SPECIAL FUNCTIONS DATA AREA

i. Outputs and its contact OUT

ii. Timers and contacts TIM

iii. Counters and contacts CNT

iv. Auxiliary relays and its contacts AR

v. Special relays and its contacts SR

vi. Holding relays and its contacts HR

vii. Link relays and its contacts LR

viii. Temporary relays and its contacts TR

SELECTING A PLC

Points to consider when selecting a PLC:

i. Input/Output capacity - numbers of I/O

ii. Types of input/output required - relay/transistor

PLC


iii. PLC size

iv. Memory size

v. Types of software languages

vi. Future expension of systems

vii. Support and backup.

Documents

Intro to PLC 0135044660