AU2 PLC Conveyo 28May2010

8/2/2019 AU2 PLC Conveyo 28May2010

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ERT3026 Automation

Experiment AU2: Application of PLC for Conveyor Belt Control

1.0 Objective To understand the basic principles of a Programmable Logic Controller (PLC)

and its application on a Conveyor Belt System

2.0 Apparatus1. Omron Sysmac CQM1-CPU21 Programmable Logic Controller2. Omron Sysmac SYSWIN Software Version 3.33. Programmable Console PR0014. Pentium PC5. Conveyor Belt System6. Sensor switch7. D-type connector

3.0 Introduction to Programmable Logic ControllerA PLC is a computer-based control system that uses program instructions to makedecisions. Thus, PLC is basically an event-driven device, that is, an event-taking place

will result in an operation which generates an output.

PLC is widely used in industry for controlling manufacturing process because of the

following advantages:

Wide range of control application Easy control modification Shorter training time and easy maintenance Highly reliable and efficient Capability to withstand harsh and/or noisy factory environment

Thus, a PLC provides control in manufacturing lines and system such as automaticequipments, the NC machines, and industrial robots. These can be divided into threecategories:-

(i) Sequence control: Conventional relay control logic Timers / counters Printer Circuit Board (PCB) card controller replacing counters Auto/semi-auto/manual control of machine and processes

(ii) Sophisticated control: Arithmetic operation ),,,( Information handling Analog control (temperature, pressure and etc) Proportional-integral-derivative (PID) controller Servomotor and stepper motor controls


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(iii) Supervisory control: Process monitoring and alarm Fault diagnosis and monitoring Interface with computer (through RS232C/ RS422) Printer / ASCII interface Factory automation networking Local Area Networking Wide Area Network

The Basic Components of PLC

A typical PLC can be divided into three parts namely:-

1. Input/Output (I/O) modules2. Processor3.

Programming Device

The following figure shows the three main units: Programming Device; Input/Output

Modules and Processor Unit.

Figure 1. Major components of a PLC.

1. I/O modulesThe input modules interface with the input devices such as push buttons, limit

switches, sensors, and switches to the terminal of the input modules. Thesemodules convert the input signals from the machine or process devices into

signals that can be used by the controller.

The output devices interface with the output devises such as motors, motor

starters, solenoid valves and indicator lamps that are hardwired to the terminals on

the output modules. These modules convert controller signals into external signals

that can be used to control the machine or process.


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The purpose of Input/Output modules of PLC is to interface its internal circuitryto outside equipments. There are four (4) basic functions served:

Termination. Each I/O module provides terminal connections to which fielddevices can be connected. Each terminal is assigned an ID number.

Signal conditioning. Most of the voltages used by field devices are notcompatible with the low DC voltage data signals processed inside the PLC.

Module converts external signals to a voltage suitable for PLC.

Isolation. The factory floor is a very noisy environment. Noise is created bystray magnetic fields produced by devices such as large motors, welding

equipment, and contactors used to switch high currents on and off. Themodules isolate the processor unit by using opto-couplers.

Indication. Each terminal has an associate indicator. Its function is toilluminate when a voltage is applied to that terminal. I/O modules use either

LEDs or neon light bulbs as indicators.

Figure 2. AC input module.

Figure 2 shows an AC input module. It can convert the presence of 240V applied to its

input terminals as a logic 1 state; and the absence of which produces 0 logic state. InFigure 2:


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(i) A NO limit switch is connected between L1 and input terminal. An ACpotential difference is applied between L1 and L2 when the switch is closed;

(ii) A neon lamp and a series resistor are connected across the input terminal andL2, indicating voltage presence, R1 is current limiting resistor.

(iii) R2 and R3 are used to drop most of the incoming voltage, so that remainingvoltage of 5-10V is applied to full-wave bridge rectifier that converts AC to a

pulsating DC voltage.

(iv) Capacitor C1 is used to filter out the electrical noise from input line.(v) Optocoupler is used to isolate processor unit from input terminal.

The DC output module interfaces the logic signal from the processor with a DC output

field device that operates at a potential greater than +5 volts. Figure 3 shows an outputmodule:

Figure 3. DC output module.

(i) When the processor generates logic 1, LED in the optical coupler is forwardbiased and it turns on the phototransistor, PT1.

(ii) Q1 is switched on and current flows through R3 and a 5V voltage appears atterminal 4. It activates solenoid and also causes the LED indicator to light.

Figure 3(b) shows how external field devices are connected to the DC output terminal.

When one of the output circuits is energized by the processor unit, it enables current toflow from V through the output field device, through Q1 to +V.

2. ProcessorThe processor holds and executes the user-program which is the sequence of

instructions that the user created to control the industrial machine or process. In

order to carry out the job, the processor must store the most-up-to-date input andoutput conditions.

The input conditions are stored in the input image file, which is a portion of the

processors memory, that is, the assigned address of every single input terminal.


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Likewise the output condition is stored in the output image file, which is another

portion of the processors memory assigned to the output terminal. Various PLCsystems have their own methods of assigning addresses.

Center Processing Unit (CPU)

The CPU is the brain of a PLC, the intelligence is performed by microprocessor(s)

in interpreting and executing programs written by PLC manufacturer to enablePLC perform ladder logic instead of other programming language. The ALU

performs mathematical calculations and make a logic decision. The CPU is the

components of the processor that actually performs the user-program. It is

continually and immediately updating the output image file. In other words, if aninstruction execution calls for a change at one of the output image file locations,

that change is effected immediately, before the processor proceeds to the next

instruction.

3. Programming DevicesThe essential part of PLC is the programming device, which is also called theprogramming terminal, console, desktop or computer. It allows the user to enter,

edit and monitor programs by connecting into the processor unit and allow access

to the memory.

4. Relationship of Memory Word Address to I/O modules

Figure 4 illustrates the addressing scheme, shows the internal connections of a PLC, and

helps to clarify the sequence of events that takes place when an input field switch closurecauses an output field lamp to turn on.

Figure 4. Relationship of bit addresses to input and output devices.


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The operation sequence: The switch is connected to terminal 112/12 of the input module

and the lamp is connected to terminal 013/06 of the output module.

1. When the switch closes, it causes a 1 to be stored into bit 112/12 of the inputimage table

2. The input contacted the ladder and is also assigned with the number 112/12. Thisnumerical indicator instructs the user program to close the contact if a 1 is

present at memory bit 112/12.3. The output is energized when the rung is true.4. A 1 is stored at the bit. The output image table with the same address as the

number assigned to the energized output device on the ladder rung.

5. A 1 at memory bit 013/06 causes the terminal on the Output Module with thesame ID number to be actuated.

6. A voltage at the output terminal 013/06 turns ON the lamp.5 Ladder Diagram Programming

Ladder logic diagram is used by most brands of PLCs. The ladder logic resembles

hardwired relay circuits. The symbols represent an instruction set that performs differenttypes of On-Off operations. In general, the input conditions are represented by contact

symbols, and the output instructions are represented by coil symbols. Fig. 5 compares a

relay diagram to a ladder diagram rung:

Figure 5(a). Relay diagram.

Figure 5(b). Ladder diagram rung.

Status of input and output devices, for which On/Off are represented by 1 or 0 bit,are stored in unique bit locations or bit address, e.g., 02, 03 and 16 in Fig. 5(b). These are

stored in word locations or address at 113 and 012. The address numbers correspond to

the location of I/O location of the I/O modules and the terminal to which each fielddevice is wired.


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6 Ladder Programming Symbols

Table 1 summarizes 5 major types of operations and shows the instruction symbols usedwithin these categories. These are commonly used to perform relay logic type operations.

Table 1 Ladder programming symbols


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In this PLC experiment, students are requested to run the following six programs. The

programs are written to instruct PLC to control the conveyor belt system.

Program 1

1) Load SYSWIN (Omron PLC software) from the PC terminal and establish

connection to the PLC (online\connect).

2) Use the ladder diagram editor to construct the following ladder diagram as shownin Figure 6. The END (01) commands is input using FUN function command.

3) Load and run the program by executing the followings:-

online \ mode \ Stop/Prog

online \ Download program to PLC

online \ mode \ Run

Figure 6. The ladder diagram of program 1

4) Notice the change at the output 00 for different value from input 0 and 2.5) Stop the PLC and connect the DC motor of the conveyer as below (Figure 7).

Figure 7. Connecting the DC motor with +/- 12 V DC supply source

00 04

01 05

02 06

03 06 (PLCs output A)

(+) Motor ( - )

+ 12V

- 12V

0 V


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6) Run the PLC and demonstrate the running and stopping of the conveyer.7) Power the optical switch (Brown to +24v, Blue to 0V) that is mounted on the

conveyor belt.

8) Make sure the input switch 2 is off and connect the output of the opticalswitch (Black) to input 2.

9) Run the PLC again and demonstrate the stopping of the conveyer if the opticalswitch detects the presence of an object.

10) Write a report to summarize the activities of the above exercise

Program 2.

1) Use the ladder diagram editor to construct the following ladder diagram(Figure 8).


2) Load and run the program.3) Demonstrate the bi-direction running of the conveyer.4) Write a report summarising the activities of the above exercise

Program 3

1) Construct the following ladder diagram (Figure 9).


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2) In the parameter of the counter, set the counter number and its value. Theimmediate value of the counter is entered following the character #.

3) Disconnect the optical switch and the conveyer from the PLC and demonstratethe running of Counter by switching the input switches 02 and 01.

4) Connect the optical switch and the conveyer back to the PLC and demonstratethe stopping of conveyer if three objects are counted.

5) Write a report to summarize the activities of the above exerciseProgram 4



2) Load and run the PLC to demonstrate the running of the timer.


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Program 5



2) Connect the conveyer to the PLC following the schematic in Program1.3) Connect the output of the optical switch to input 02.4) Load and run the program.5) Demonstrate the application of counter and timer in a conveyer system.6) Write a report summarising the activities of the above exercise.

Program 6

1) Construct the following ladder diagram (Figure 12). Run the program todemonstrate the bi-directional control of a conveyer system.



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Lab Quiz:-

After the lab section, student is requested to attend the lab quiz individually. Please

obtain the lab quiz from lab supervisor. Each lab quiz carries 25% of the total lab mark.

And the lab quiz is given 1 hour to complete and need to be submitted on the same day.

Note: Students are requested to submit their lab reports by handwriting.

Prepared By:

Associate Professor Dr. Ir. Sim Kok SweeMMU, FET

Melaka Campus

27/March/2004Revised on 29/April/2005

Revised on 31/May/2007

Revised on 21/May/2008Revised on 8/May/2009

Revised on 27/May/2010

Documents

AU2 PLC Conveyo 28May2010