control manual 1

8/3/2019 Control Manual 1

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Lab Manual

Control Systems (EEE325)

2nd

Edition

August 2011

Department of Electrical Engineering,

COMSATS Institute of Information Technology (CIIT),

Islamabad

Name: _________________________________Year: __________________________________

Batch: _________________________________

Roll No: ________________________________

Majors: BCE BTE


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Experiment 1

Introduction to PLCs and Implementation of

Combinational Logic through Ladder Logic

Objectives:

To understand the basics of PLCs and their programming using ladder logic.

Equipment/Tools required:

Trilogi PLC, PC with Trilogi software, connecting leads etc.

Introduction:

A programmable logic controller (PLC) is a specialized computer used to

control machines and processes. It uses a programmable memory to store instructions

and execute specific functions that include on/off control, timing, counting,

sequencing, Arithmetic and data handling. The design of most PLCs is similar to that

of other computers. Basically, the PLC is an assembly of solid-state digital logic

elements designed to make logical decisions and provide outputs. Programmable

logic controllers are used for the control and operation of manufacturing process

equipment and machinery.

The programmable logic controller is basically a computer designed for use in

machine control. It has been designed to operate in the industrial environment and is

equipped with special input/output interfaces and a control programming language.

Initially the PLC was used to replace relay logic, but its ever-increasing range of

functions means that it is found in many and more complex applications. Because the

structure of a PLC is based on the same principles as those employed in computer

architecture. It is capable not only of performing relay switching tasks but also of

performing other applications such as counting, calculating, comparing and the

processing of analog signals.


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Parts of PLC:

A typical PLC can be divided into following parts: (Figure 1.1)

Central processing unit (CPU).

Input/Output (l/O) section. Power supply. Programming device.

Fig. 1.1 Parts of PLC

PLC Scan Cycle:

During each operating cycle, the processor reads all the inputs, takes thesevalues and energizes or de-energizes the outputs according to the user program. This

process is known as a scan. A typical PLC scan is shown in Figure 1.2 in which PLC

scan I/O and program. Since inputs may change continuously so PLC must carry on

this process continuously. The PLC scan time specification indicates how fast the

controller can react to changes in inputs. Scan time varies with program content and

length. The time required to make a single scan can vary from about 1ms to 20ms.

Fig. 1.2 PLC scan cycle


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PLC Programm

According to Int

standard, PLC can b

Ladder diagr Function Blo Statement lis Structured te Sequential fu

Ladder Diagra

Ladder Diag

similar to the relay

function of the lad

conditions. This co

ladder rung. In gen

contact instructions,

the coil symbol.

Contacts and C

Normally ONormally op

Normally ClNormally cl

Coil

3

ng:

ernational Electrotechnical Commission (IE

programmed using following five different

am (logic).

ck Diagrams (FBDs).

ts.

xt languages.

nction charts.

s:

ram is graphical depiction of a process

ladder logic schemes that were replaced

er logic diagram program is to control ou

trol is accomplished through the use of wh

ral, a rung consists of a set of input condi

and an output instruction at the end of the r

ils:

en

n contact and is short circuited when energi

sed

sed contact and is converted to open circuit

) 61131-3/EN 6131

languages:

ith rungs of logic,

by PLCs. The main

puts based on input

at is referred to as a

ions, represented by

ng is represented by

ed.

hen energized.


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Implementation of AND, OR and NOT Gates using Trilogi:

Fig. 1.3 Gates implementation

Lab. Tasks:

Lab Task No 1:Create a three input NAND Gate and three inputs NOR Gate.

Lab Task No 2 (Mixer process control problem):o A mixer motor is used to automatically stir the liquid in a tank when the

temperature and pressure reach preset values. In addition, direct manual

operation of the motor is provided by means of a separate pushbutton station.

The process is monitored with temperature and pressure sensors switches that

close their respective contacts when conditions reach their preset values.


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o Additionally the change requires that the manual pushbutton control should bepermitted to operate at any pressure but not unless the specified temperature

setting has been reached.

Fig. 1.4 Mixer process control

Lab Task No 3 (Filling operation):

A continuous filling operation requires boxes moving on a conveyor to be

automatically positioned and filled. The operation sequence is as follows:

o The conveyor starts when the START button is momentarily pressed and Stopwhen the STOP button is momentarily pressed.

o When the process is operating it energize the RUN status light.o When the process stops it energize the STANDBY status light.o When box reaches right edge and sensed by PHOTOSENSOR, the conveyor

stops and energizes the STANDBY light.

o When the box is in position and the conveyor is stopped. The SOLENOIDvalve opens and allows box to be filled. Filling stops, when LEVEL sensor

goes true.

o When the box is full. The FULL light should remain energized until the boxclear o the PHOTOSENSOR.


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Fig. 1.5 Filling operation

Note: START: NO contacts

STOP: NC contacts

Level switch, Photo switch: NO contacts

Home Tasks:

1. Implement Flip-Flop using both NAND and NOR Gates.Truth Table of NOR Gate

Table 1.1 NOR truth table

S R Q Q1 0 1 0

0 0 1 0

0 1 0 1

0 0 0 1

1 1 0 0

Truth Table of NAND Gate

Table 1.2 NAND truth table

S R Q Q1 0 0 1

1 1 0 1

0 1 1 0

1 1 1 0

0 0 1 1

2. Implement 3 to 8 line decoder.

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