Internship Report

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TABLE OF CONTENTS PAGE

1: INTRODUCTION 2

2: DEPARTMENT 3

3: INSTRUCTOR 4

4: BASIC STAR AND DELTA CONNECTIONS 4

5: 3 φ INDUCTION MOTOR STARTER (STAR TO DELTA) 6

6: CONTROL OF 3 φ INDUCTION MOTOR (FORWARD AND REVERSE) 10

7: INTRODUCTION TO PLC 12

8: PLC LANGUAGES, VENDORS & FEATURES 12

9: PLC TYPES 13

10: PLC HARDWARE 14

11: PLC PROGRAMMING 18

12: LADDER LOGIC 18

13: BASIC DIGITAL LOGIC FUNCTIONS 19

14: PLC IN SERVICE INDUSTRIES (TYRE DIVISION SECTION) 22

15: PROGRAMMS 23

16: AUTOMATION OF PRODUCT PACKAGING 23

17: AUTOMATION OF STORAGE DOOR 27

18: VARIABLE FREQUENCY DRIVE (VFD) 29

ENGR. SULAMAN ZEESHAN IQBAL

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INTRODUCTION

It is pleasure and honor for me, that I spent my precious time as an interne in Ser-vice Industries Private Limited Gujrat (PAKISTAN). It was really practical and wonderful experience. I wanted to get traning and experience related to PLC and Service industry is one of those industries in which 70 persent machinery is con-trolled with the help of PLC. So, I got traning and now I have sound knowledge and experience related to PLC.

HISTORY OF INDUSTRY

Ch. Nazar Muhammad, Ch. Muhammad Hussain and Ch. Muhammad Saeed started their business in 1941 from the manufacturing of hand bags and they started the production of footwear in 1954.

Products of SERVIS

Leather Shoes Sports Shoes Canvas Shoes Rubber Sandals Rubber Slippers Safety Shoes Footwear for Defense Forces Tyres and Tubes for Bicycles, Motor Bikes and Cars

Servis Shoes Brands

Don Carlos (N Dure, Maximus, Breezers, Classic) Cheetah Calza Liza Toz Skooz

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General Manager

Ghulam Ahmad Cheema is present general manager of Service Industries limited.

DEPARTMENT

Tyre Division (Electrical)

I worked in Electrical department of tyre division section. All the staff of electrical department was very co-operative with me especially my instructor. In electrical department faults related to electrical part of machinery is resolved. Such as, if the electrical part of some machinery is out of order such as Fuse, Circuit Breaker, re-lay, timer, motor winding and etc then technicians solve the problem. The hierar-chy of people in electrical department is follows:

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MANAGER

SENIOR ENGINEER

SENIOR SUPERVISIOR

SHIFT ENGINEER

SHIFT INCHARGE

WORKERS AND TECHNICIANS

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INSTRUCTOR

My instructor name was Engr. Sulaman. He is expert in plc hardware and program-ming. He has also excellent management skills. He started to teach me from basics and then in very short time, I understood and studied all essentials of PLC hard-ware and programming. Now I am able to understand and read complex PLC pro-grams of large machines such as ULT tyre section press machine and etc. My in-structor also guided me how to manage staff members as well as office work. To solve the big issues such as related to PLC, technicians’ refer this to Engr. SULA-MAN. Sir SULAMAN which has great experience solves the problems in minutes and save a lot of time. In this way they manage all things in efficient way.

BASIC STAR AND DELTA CONNECTIONS

STAR CONNECTION

In this kind of interconnection, the starting ends or finishing ends (Similar ends) of three coils are connected together to form the neutral point. Or Star Connection is obtained by connecting together similar ends of the three coils, either “Starting” or “finishing”. The other ends are joined to the line wires. The common point is called the neutral or Star Point, which is represented by N.

DELTA CONNECTION

In this system of interconnection, the starting ends of the three phases or coils are connected to the finishing ends of the coil. Or the starting end of the first coil is connected to the finishing end of the second coil and so on (for all three coils) and it looks like a closed mesh or circuit Three wires are taken out from three junctions and the all outgoing currents from junction assumed to be positive. In more clear words, all three coils are connected in series to form a close mesh or circuit. 

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 IN STAR CONNECTION

VL = √3 VPH or VL = √3 EPH

Line Current = Phase Current

IL = IPH

Total Power = P = 3 x VPH x IPH x CosФ  OR P = √3 x VL x IL x CosФ

IN DELTA CONNECTION

VL = VPH

I.e. in Delta connection, the Line Voltage is equal to the Phase Voltage.

IL = √3 IPH

Total Power = P = 3 x VPH x IPH x CosФ  OR P = √3 x VL x IL x CosФ

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3 φ INDUCTION MOTOR STARTER (STAR TO DELTA)

WHY WE USE STAR TO DELTA?

Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed. During starting the motor windings are first connected in star connection this causes the reduction of voltages by 3. This also reduces the torque by 3. After a period of time the windings are reconfigured as delta and the motor runs normally.

CIRCUIT DIAGRAM OF STAR –DELTA STARTER

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WORKING

The main circuit breaker serves as the main power supply switch that sup-plies electricity to the power circuit.

The main contactor connects the reference source voltage R, Y, B to the pri-mary terminal of the motor U1, V1, W1.

In operation, the Main Contactor (KM3) and the Star Contactor (KM1) are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor (KM2) is closed. The control of the contactors is by the timer (K1T) built into the starter. The Star and Delta are electrically interlocked and preferably mechanically interlocked as well.

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Controlling the interchanging star connection and delta connection of an AC induc-tion motor is achieved by means of a star delta or wye delta control circuit. The control circuit consists of push button switches, auxiliary contacts and a timer.

CONTROL CIRCUIT OF STAR-DELTA STARTER

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WORKING

The ON push button starts the circuit by initially energizing Star Contactor Coil (KM1) of star circuit and Timer Coil (KT) circuit.

When Star Contactor Coil (KM1) energized, Star Main and Auxiliary con-tactor change its position from NO to NC.

When Star Auxiliary Contactor (1)( which is placed on Main Contactor coil circuit )became NO to NC it’s complete The Circuit of Main contactor Coil (KM3) so Main Contactor Coil energized and Main Contactor’s  Main and Auxiliary Contactor Change its Position from NO To NC. This sequence happens in a friction of time.

After pushing the ON push button switch, the auxiliary contact of the main contactor coil (2) which is connected in parallel across the ON push button will become NO to NC, thereby providing a latch to hold the main contactor coil activated which eventually maintains the control circuit active even after releasing the ON push button switch.

When Star Main Contactor (KM1) close its connect Motor connects on STAR and it’s connected in STAR until Time Delay Auxiliary contact KT (3) become NC to NO.

Once the time delay is reached its specified Time, the timer’s auxiliary con-tacts (KT)(3) in Star Coil circuit will change its position from NC to NO and at the Same Time  Auxiliary contactor (KT) in Delta Coil Circuit(4) change its Position from NO To NC so Delta coil energized and  Delta Main Con-tactor becomes NO To NC. Now Motor terminal connection change from star to delta connection.

A normally close auxiliary contact from both star and delta contactors (5&6)are also placed opposite of both star and delta contactor coils, these in-terlock contacts serves as safety switches to prevent simultaneous activation of both star and delta contactor coils, so that one cannot be activated without the other deactivated first. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active.

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The control circuit above also provides two interrupting contacts to shut-down the motor. The OFF push button switch break the control circuit and the motor when necessary. The thermal overload contact is a protective de-vice which automatically opens the STOP Control circuit in case when mo-tor overload current is detected by the thermal overload relay, this is to pre-vent burning of the motor in case of excessive load beyond the rated capac-ity of the motor is detected by the thermal overload relay.

At some point during starting it is necessary to change from a star connected winding to a delta connected winding. Power and control circuits can be ar-ranged to this in one of two ways – open transition or closed transition.

CONTROL OF 3 φ INDUCTION MOTOR (FORWARD AND RE-VERSE) POWER DIAGRAM

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CONTROL OF 3 φ INDUCTION MOTOR (FORWARD AND RE-VERSE) CONTROL DIAGRAM

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INTRODUCTION TO PLC

DEFINATION 1

It is a programmable interface between input devices like push buttons, limit switches etc and final control element like actuators, relays, motors, solenoid valves and status indicating output devices like lamp, led, hooters and etc.

DEFINATION 2 (BY NATIONAL ELECTRICALMANUFACTURE ASSO-CIATION_)

PLC is "A digitally operating electronic apparatus that uses a programmable mem-ory for internal storage of instructions for implementing specifics functions, such as logic sequencing, timing, counting, and arithmetic, to control, through digital or analogue input/output modules, various machines or processes".

PLC LANGUAGES, VENDORS & FEATURES

PLC LANGUAGES

Ladder diagram (mostly use every where) Functional block diagram (FBD) Sequential functional chart (SFC) Structured text language (ST)

PLC VENDORS

Siemens Allen bradley Schneider Beckhoff Mitsubishi Messing Ge – Fanuc Omron

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PLC FEATURES

Sequential logic solver Bit operation Data transfer Text handling PID calculation Subroutines

PLC TYPES

COMPACT

In Compact PLC CPU unit, Communication Port, Power Supply unit, Inputs and Outputs all are mounted on a single board.

I/O capacity of Compact PLC is less than I/O capacity of Modular PLC.

Generally used for small applications such as Hydraulic press machine, any Special Purpose machine (SPM), etc. 

Modular PLC

In Modular PLC consisting separate parts as described below:-

1. Base Rack,

2. Power Supply Module,

3. CPU Module,

4. Input Modules,

5. Output Modules,

I/O capacity of Modular PLC is more than I/O capacity of Compact PLC.

Generally used for large Application Such as Plant Automation, Power Plant Handling, etc.

In Modular PLC there is also some Small PLC ( i.e. Nexgen 2K, Nexgen 5K)available which we can use in Small applications.

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PLC HARDWARE

I/O SECTION

The I/O section establish the interfacing between physical devices in the real world outside the PLC and the dig-ital arena inside the PLC.

The input module has bank of terminals for physically connecting input devices, like push buttons, limit switches etc. to a PLC. the role of an input module is to translate signals from input devices into a form that the

PLC's CPU can understand.

The Output module also has bank of terminals that physically connect output de-vices like solenoids, motor starters, indicating lamps etc. to a PLC. The role of an output module is to translate signals from the PLC's CPU into a form that the out-put device can use.

The tasks of the I/O section can be classified as:

Conditioning

Isolation 

Termination

Indication

CPU SECTION

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The Central Processing Unit, the brain of the system is the control portion of the PLC. It has three Subparts.

Memory System

Processor

Power Supply 

MEMORY SYSTEM:-

The memory is the area of the CPU in which data and information is stored and re-trieved.The total memory area can be subdivided into the following four Sections.

I/O IMAGE MEMORY

The input image memory consists of memory locations used to hold the ON or OFF states of each input field devices, in the input status file.

The output status file consists of memory locations that stores the ON or OFF states of hardware output devices in the field. Data is stored in the output status file as a result of solving user program and is waiting to be transferred to the output module's switching device.

DATA MEMORY

It is used to store numerical data required in math calculation, bar code data etc.

USER MEMORY

 It contains user's application program.

EXECUTIVE MEMORY

 It is used to store an executive program or system software . An operating system of the PLC is a special program that controls the action of CPU and consequently the execution of the user's program. A PLC operating system s designed to scan image memory, interprets the instruction of user's program stored in main memory,

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and executes the user's application program the operating system is supplied by the PLC manufacturer and is permanently held in memory.

PROCESSOR

 The processor, the heart of CPU is the computerized part of the CPU in the form of Microprocessor / Micro controller chip. It supervises all operation in the system and performs all tasks necessary to fulfill the PLC function.

It reads the information i.e status of externally connected input devices with input module.

It stores this information in memory for later use.

It carries out mathematical and logic operations as specified in application program.

After solving the user's program, it writes the result values in the memory.

It sends data out to external devices like output module, so as to actuate field hardware.

It performs peripheral and external device communication.

It performs self diagnostics.

 

POWER SUPPLY

The power supply provides power to memory system, processor and I/O Modules.

It converts the higher level AC line Voltage to various operational DC val-ues.

For electronic circuitry.

It filters and regulates the DC voltages to ensure proper computer opera-tions.

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Programmer/Monitor:-

The Programmer/Monitor (PM) is a device used to communicate with the circuits of the PLC.The programming unit allows the engineer/technicians to en-ter the edit the program to be executed.

In its simplest form it can be hand-held device with membrane keypad for pro-gram entry and a display device (LED or LCD) for viewing program steps of func-tions.

More advanced systems employ a separate industrial terminal or personal comput-ers with type-writer type keyboard and CRT monitors. With the help of proprietary software, it allows programmer to write, view and edit the program and download it into the PLC. It also allows user to monitor the PLC as it is running the program. With this monitoring systems, such things as internal coils, registers, timers and other items not visible externally can be monitored to determine proper operation. Also,internal register data can be altered, if required. to fine tune program opera-tion while debugging communication between PM and PLC is done via a cable connected to a special programming port on PLC. connection to the personal com-puter can be through a serial port or from a dedicated card installed in the com-puter.

PLC PROGRAMMING

DIGITAL I/O

Inputs are push buttons, limit switches, photo sensors and ets. common out put de-vices include relays, motor starters and solenoid valves.

ANALOG I/O

Inputs are transmitters used for sensing various parameters. Common output sig-nals are (motor speed, valve position, air pressure and etc).

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LADDER LOGIC

"LADDER" DIAGRAMS

Ladder diagrams are specialized schematics commonly used to document industrial control logic systems. They are called "ladder" diagrams because they resemble a ladder, with two vertical rails (supply power) and as many "rungs" (horizontal lines) as there are control circuits to represent. If we wanted to draw a simple lad-der diagram showing a lamp that is controlled by a hand switch, it would look like this:

The "L1" and "L2" designations refer to the two poles of a 120 VAC supply, unless otherwise noted. L1 is the "hot" conductor, and L2 is the grounded ("neutral") conductor. 

BASIC DIGITAL LOGIC FUNCTIONS

AND FUNCTION

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OR FUNCTION

NOT FUNCTION

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NAND FUNCTION

NOR FUNCTION

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Exclusive-OR function

If we wish to invert the output of any switch-generated logic function, we must use a relay with a normally-closed contact. For instance, if we want to energize a load based on the inverse, or NOT, of a normally-open contact, we could do this:

We will call the relay, "control relay 1," or CR1. When the coil of CR1 (symbolized with the pair of parentheses on the first rung) is energized, the contact on the sec-ond rung opens, thus de-energizing the lamp. From switch A to the coil of CR1, the logic function is noninverted. The normally-closed contact actuated by relay coil CR1 provides a logical inverter function to drive the lamp opposite that of the switch's actuation status.

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PLC IN SERVICE INDUSTRIES (TYRE DIVISION SECTION)

In tyre division section of Service Industries all machines are working at MIT-SUBISHI’S plc modules (FX2N & FX3U). I got training of FX2N.

MITSUBISHI FX2N & FX3U

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PROGRAMMS

AUTOMATION OF PRODUCT PACKAGING

Product packaging is one of the most frequent cases for automation in industry. It can be encountered with small machines (ex. packaging grain like food products) and large systems such as machines for packaging medications. Example we are showing here solves the classic packaging problem with few elements of automa-tion. Small number of needed inputs and outputs provides for the use of CPM1A PLC controller which represents simple and economical solution.

By pushing START key you activate Flag1 which represents an assisting flag (Segment 1) that comes up as a condition in further program (resetting depends only on a STOP key). When started, motor of an conveyor for boxes is activated. The conveyor takes a box up to the limit switch, and a motor stops then (Segment 4). Condition for starting a conveyor with apples is actually a limit switch for a

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box. When a box is detected, a conveyor with apples starts moving (Segment 2). Presence of the box allows counter to count 10 apples through a sensor used for ap-ples and to generate counter CNT010 flag which is a condition for new activation of a conveyor with boxes (Segment 3). When the conveyor with boxes has been ac-tivated, limit switch resets counter which is again ready to count 10 apples. Opera-tions repeat until STOP key is pressed when condition for setting Flag1 is lost. Pic-ture below gives a time diagram for a packaging line signal.

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LADDER DIAGRAM

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AUTOMATION OF STORAGE DOOR

Storage door or any door for that matter can be automated, so that man does not have to be directly involved in their being opened or closed. By applying one three-phased  motor where you can change direction of its movement, doors can be lifted up and lowered back down. Ultrasonic sensor is used in recognizing presence of a vehicle by the doors, and photo-electric sensor is used to register a passing ve-hicle. When a vehicle approaches, the doors move up, and when a vehicle passes through the door (a ray of light is interrupted on photo-electric sensor) they lower down.  

By setting a bit IR000.00 at the PLC controller input where ultra-sonic sensor is connected, output IR010.00 (a switch is attached to

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this output) is activated, so that a motor lifts the doors up. Aside from this condi-tion, the power source for lifting the doors must not be active (IR010.01) and the doors must not be in upper position already (IR000.02). Condition for upper limit switch is given as normally closed, so change of its status from OFF to ON (when doors are lifted) will end a condition for bit IR010.00 where power source for lift-ing the doors is (Segment 1).Photo-electric switch registers a vehicle that passes by, and sets flag IR200.00. DIFD instruction is used. This instruction is activated when a condition that pre-cedes it changes status from ON to OFF. When a vehicle passes through a door, it interrupts a ray and bit IR000.01 status changes from ON to OFF (Segment 2).  

By changing status of an assisting flag from OFF to ON a condition for lowering a door is executed (Segment 3). Aside from this condition, it is necessary that a unit power source for lifting a door is turned off, and that door is not in lower position already. Bit which operates this power source for lowering, IR010.01 is automatic, so doors are lowered until they come to the bottom limit switch which is repre-sented in a condition as normally closed. Its status change from OFF to ON inter-rupts a condition of the power source for lowering doors. With oncoming new ve-hicle, cycle is repeated. 

LADDER DIAGRAM

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VARIABLE FREQUENCY DRIVE (VFD)

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor.

Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.

A VFD is used extensively in modern facilities to save energy on mechanical sys-tems, such as motors, pumps, etc. Selected to match motor curves to ensure speed and loads are matched, VFDs can help save motor energy by allowing for variable flow of air, water, etc., based on the demands and needs of a particular site. This is accomplished by converting the fixed frequency of incoming alternating current (AC) voltage to direct current (DC) and then reconverting it back to AC voltage by varying the frequency at which the insulated gate bipolar transistors (IGBTs) are gated on and off.

WORKING

A VFD operates by converting the input sinusoidal AC voltage to DC voltage and then back to AC voltage. This conversion occurs by using either silicon-controlled rectifiers (SCRs) or IGBTs. The DC voltage is switched using IGBTs to create an AC output voltage (called the inverter). The IGBT can switch on and off to create an AC voltage waveform that delivers power to the motor. The IGBTs create an AC waveform by using pulse width-modulated (PWM). The frequency at which the switching occurs, which varies from manufacturer to manufacturer, is called “carrier frequency.”

A typical 6-pulse VFD has six diodes as a front-end bridge rectifier that converts AC to DC. VFDs can also have 12 diodes two sets per phase (2 × 2 × 3 = 12 pulse) or 18 diodes three sets per phase (3 × 2 × 3 = 18 pulse) and so on .One set of diodes is supplied by a Delta-Y transformer to create a phase shift on the AC side between the two rectifiers to reduce harmonics reflected back to the source.

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6-PULSE VFD

A 6-pulse VFD develops the output DC voltage by taking each phase of the AC source and installing one set of diodes to gate on and off A 6-pulse VFD is most commonly used in the building system. Typical current total harmonic distortion (THD) back to the source can be as high as 35% at the input terminals of the VFD. You can install an inline inductor to reduce the reflected harmonics back to the point of coupling. The inductor reduces the current distortion and thus the voltage distortion at the source. The input line inductors are typically 3% to 5% imped-ance. Base the selection of the inductor on harmonic evaluation of the electrical system at the building, impact of voltage drops across the inductor, and impact of power factor to the building electrical system.

The impact of harmonics should take into account available fault current (i.e., the stiffness of the electrical system).

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