Academy Of Industrial Automation & Technology

PROJECT REPORT ON

Automatic Tank Level Control Using PLC ( Siemens ) and SCADA

By

1. Ritu Varsha

2. Shalini Kumari

3. Shayanti Ghosh

Stream : AEIE

College : Techno India College Of Technology

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INDEX

________________________________________________________

1. Acknowledgement

2. Objective od the project

3. Introduction

4. PLC architecture

5. Starters

6. Scaling & SCADA

7. Project

8. Ladder Diagram

9. Visual representation in SCADA

10. Algorithm

11. Conclusion

12. Bibliography

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Acknowledgement

At the end of my thesis I would like to thank all those people who made

this thesis possible. First of all, I would like to express my deepest sense of

Gratitude to Mrs. Sukla Goswami who offered her continuous advice and encouragement throughout the course of this thesis. I thank him for the

systematic guidance and great effort he put into training me in the scientific field

I would like to express my very sincere gratitude to the college authorities and

management for making all this possible. Finally, I take this opportunity to

express the profound gratitude from my deep heart to my beloved parents and

friends for their love and continuous support both spiritually and materially.

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Objective of the project:

1. Understanding the programmable logic controller and its peripherals.

2. Programming the PLC with the STEP 7 software.

3. Applying the PLC to automatically control the liquid level in a tank so that

water is going waste due to overflow of tanks can be saved easily.

Automatically controlling the tank levels by the use of PLC helps to eliminate much of the hard wiring that is associated with conventional relay control circuits. Through this project the tank levels can be maintained upto a desired level and the water or some other sort of liquid can be prevented from over flow.

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INTRODUCTION TO PLC

A programmable logic controller (PLC) is a specialized computer used to control machines and process. It uses a programmable memory to store instructions and specific functions that include On/Off control, timing and counting, sequencing, arithmetic, and data handling. PLC is a programmable, reusable and reliable. It could withstand a harsh industrial environment. They had no hard drive, they had battery backup. It could start in seconds. It used ladder logic for programming.

Advantages of PLC control system :-

Flexible Faster response time Less and simple wiring Solid-state- no moving parts Modular design and easy to repair and expand Handles much more complicated systems Sophisticated instruction sets available Allows for diagnostics “easy to troubleshoot” Less expensive

RELAYS:-

A relay is a simple device that uses a magnetic field to control a switch. When a voltage is applied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch. The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized.

Relays are used to isolate one voltage level from another. A PLC may be used to control the operation of a medium-voltage motor, perhaps 2,300V or 4,160V. A relay is used to energize the starter, which, in turn, switches the motor voltage while the PLC controls the relay. Wired to provide a control sequence, relays may also be used for simple control schemes where a PLC would prove uneconomical. Troubleshooting relays can be handled in short order, without having to return to the maintenance shop for the computer necessary to analyze the control sequence within the PLC.

LATCHES:-

Most switches used in PLC’s are pushbutton switches, hence we implement latching in order to keep output high for the required amount of time. When A representing START button is pushed, the output B will turn ON, and the keep B ON permanently until power is removed.

TIMERS:-

All PLC’s have timer instructions. Timers are output instructions that are internal to the programmable logic controller. Timers provide timed control of the devices that they activate or de-activate. Basic functions of timer

• Timers are used to delay an action.

• Timers are used to run an operation for a predetermined period of time.

• Timers are also used to record the total accumulated time of continuous or intermediate events.

Timer’s instructions Timers consists of following parts: timer address, preset value, timer base, and accumulated value.

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There are 3 types of timers: On- delay timer, Off-delay timer, and retentive timer.

On delay timer

• Use this instruction to program a time delay after instructions become true.

• On – delay timers are used when an action is to begin a specified time after the input becomes true. For example, a certain step in the manufacturing is to begin 45 seconds after a signal is received from a limit switch. The 45- seconds delay is the on-delay timers preset value.

Off- delay timer

• Off- delay timer instructions is used to program a time delay to begin after rung input goes false.

• As an example, when an external cooling fan on a motor is provided, the fan has to run all the time the motor is running and also for certain time (say 10min) after the motor is turned off. This is a t en minute off- delay timer. The ten-minute timing period begins as soon as the motor is turned off.

Retentive timer

• Retentive timer is a timer which retains the accumulated value in case of power loss, change of processor mode or rung state going from true to false (rung state transition).

• Retentive timer can be used to track the running time of a motor for its maintenance purpose. Each time the motor is turned off, the timer will remember the motor’s elapsed running time. The next time the motor is turned on, the time will increase from there. This timer can be reset by using a reset instruction. Reset

• This instruction is used to reset the accumulated value of counter or timer.

• It is used to reset a retentive timer’s accumulated value to zero.

COUNTERS:-

Counters are used for counting a specified number of contact operations. The counters that are commonly used in control applications either count up to a preset value before triggering an event or let the event to continue until the count reaches a preset value. The different types of counter:-

Up- counters - The up-counter counts up from a current value to a preset value. These are called CTU (counter up).

Down – counter – The down counter counts down from the preset value. These are called CTD (counter down).

Up-Down counter- The up down counter counts up or down from the preset value. These are called UDC ( up down counter).

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PLC Architecture

A Programmable Logic Controller (PLC) is a device that replaces the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs as depicted in Figure 1. Today, PLCs are used in many "real world" applications such as machining, packaging, material handling, automated assembly or countless other industrial processes.

SIMATIC S7-300 PLC will be used to control the operation of a demand-actuated traffic light system in an intersection.. The general features of S7-300 are; it has a modular PLC system developed for medium performance projects, it features different modules for different automation problems, it is easy to re-program the device when an improvement is needed for the process, it is possible to be connected to communication networks such as MPI, Profibus and Industrial Ethernet, it has a vast amount of command set for programming. The S7-300 mounted on a rack is shown in Figure 2. It includes the following components: Power Supply (PS): It is required to supply the modules connected to the PLC. There are three different models for 2 A, 5 A, and 10 A max. CPU: The central processing unit. Interface Module (SM): 1. Digital Input Modules: 24 V DC transistor, 2. Digital Output Modules: 24 V DC transistor, 3. Analog Input Module: Voltage, Current, Resistor and Thermocouple,4. Analog Output Module: Voltage and Current.

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Communication Module (CP)

Programming with STEP 7:

STEP 7 software is used to program the PLC. There are three different programming languages in the STEP 7: statement list (STL) for users who prefer programming in a language similar to machine code, Ladder logic (LAD) for users who are accustomed to working with circuit diagrams, and Function Block Diagram (FBD) for users who are familiar with the logic boxes of Boolean algebra. The S7 provides a vast variety of components into its component library which in turn is useful for variable applications from conventional control applications to applications with counters, timers, flipflops, mathematical functions for industrial feed-back control processes such as PID controller design. In STEP 7, we work with addresses (absolute addressing) such as I/O signals, bit memory, counters, timers, data blocks, and function blocks. An address is the abbreviation for a particular memory area and memory location, so it is important to correctly assign the input/output (I/O) address areas in the hardware configuration and specify them in the program (STEP 7). An absolute address comprises an address identifier I (input bit), IB (input byte-8 bits), IW (input word-16 bits), ID (input double word-32 bits), Q (output bit), QB (output byte), QW (output word), QD (output double),

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M (memory bit), MB (memory byte), MW (memory word), MD (memory double word), T (timer), C (counter)] and a memory location (for example, Q 4.0, I 1.1, M 2.0, FB 21).

Figure shows the structure of an address for the input interface of a PLC.

Figure. Address structure of a PLC.

Due to the hardware structure, every input and output is assigned a default absolute address. On the other hand, the absolute address can be replaced by a freely selectable (symbolic) name (e.g. Q 4.2: Automatic mode). Symbols are assigned independent of the programming language, that is, LAD, FBD or STL.

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SATRTER

There are three types of starter.

DOL Starter RDOL Starter Star Delta Starter

DOL STARTER (Direct Online Starter)

Working of Direct-On-Line (DOL) starter:

  One method of starting electric motors is using direct on line (DOL) or across the line starter. In this method full line voltage is applied to the motor terminals. This is simplest type of motor starter. An

electrical wiring diagram for single phase DOL starter is shown below.

A DOL motor starter contains fuse and over load relay (OLR) for protection purpose. The starter can

be contain momentary contact or maintained contact push buttons. The example considered here is

momentary contact push buttons. For starting purpose normally open (NO) push button is preferred

whereas normally closed (NC) push button is used to stop the motor.  The excessive supply voltage

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drop causing high inrush current is the criteria to limit the use of DOL starter. Conveyor motors, water

pumps are the applications where DOL starters are used.

 

 

RDOL Starter (Reverse Direct Online Starter)

RDOL [Reversible DOL] starters are simply two DOL starters in the same box and allow the motor to be started in one direction and then in the other direction. REVERSIBLE DOL (RDOL) STARTER This kind of starter is required when the motor is required to run in both forward as well as reverse directions .

Ladder diagram:

Circuit diadram:

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STAR DELTA Starter

This is a starting method that reduces the starting current and starting torque. At

starting the Induction motor is star connected after it reached the approximate

operational speed it is switch to delta. The motor must be delta connected during

a normal run, in order to be able to use this starting method. This starting

method only works when the application is light loaded during the start. If the

motor is too heavily loaded, there will not be enough torque to accelerate the

motor up to speed before switching over to the delta position.

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SCALING:-

A scaling function tranforms the numerical value seen by the CPU, when it reads the analog input, into an

"engineering" value that has specific meaning. 

The conversion of a value range (e.g., -27648 to +27648 increments) to the original physical quantity

(e.g., 0 to 500 liters) is referred to as scaling.The value 27648 has simply been selected as the

maximum normal range value of any analog signal transferred to the CPU by a Siemens analog

module.This numerical value is independant of the resolution of the particular analog module used

(this is a way to standardize all scaling of analog readingsin the processor)

For unipolar data, this would mean 0 to 27648 represents full range; above 27648, overrange, below

0, underrange.

SCADA:-

SCADA stands for Supervisory Control and Data Acquisition, it is a computersystem for gathering and analyzing “real time data” SCADA systems are used to monitorand control a plant or equipment in industries.SCADA systems are used not only in industrial processes: e.g. steel making,power generation (conventional and nuclear) and distribution, chemistry, but also in someexperimental facilities such as nuclear fusion. SCADA is a computer system for gathering and analyzing “real time data”. SCADA system are used to monitor and control a plant or equipment in industries

SCADA must be able to read data from PLCs and other hardware and then toanalyze and graphically present that data to the user. SCADA systems must be able toread and write multiple sources of data.

SCADA system were developed for gathering data from far and wide using poorquality comms and providing and providing high levels of reliability and operability.Given the rapid expansion of communication systems,(satellite, cellular, fiber, microwaveetc)and the increasing processing power available at site.

Common applications for SCADA systems typically include water and wastetreatment, petroleum and hydro carbon processing, power generation, food processing,steel manufacturing, remote telecommunications and plant machinery maintenance.

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Project:

A tank of 30ft has to be scaled and maintained the level by two pumps (P1 for inlet and P2 for outlet). Both pumps should start and stop at certain level like above 25ft P1 off & p2 on, vice-versa at level of 5ft. But both pumps should not be on at the same time. The whole system is powered by a single power button. An output alarm system is there to notify if somehow level reaches at 28ft then P1 and P2 goes off. P3 will start after 3seconds and fill out the tank upto maximum level. Now P3 will be on for 5 times only right after that either P1 and P2 can’t be on because of the power goes off until the counter is reset.

Scaling:

30ft = 27648

25ft = 23040

5ft = 4608

28ft = 25804.8

Formulae:

Here,

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Algorithm:

In the simatic manager , new file is opened and the project name is given.

In the project window -> insert new object ->open simatic 300 station -> hardware.

In hardware configuration -> simatic 300-> Rack 300-> Rail The processor selected -> CPU 300 -> CPU 313C -> VT 2.6 In the program window double click on project name->CPU 313C-> S7

programs ->blocks. A new function FC1 is made by left click -> Functions -> Insert new

function. One of the programming language Ladder Logic(LAD) , Statement

List(STL) or Function Block Diagram( FBD) is selected for the function FC1 as LAD

FC1 is called in OB1 which is the organisation block then saved and downloaded.

The ladder programme is written in the function block FC1. The programme is then save-> download-> online. Inputs are given from the stimulate module and output is observed. The program is also designed in SCADA using WINCC for the visual

representation of the process.

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CONCLUSION:

A solution for water level control system using PLC is proposed, designed, implemented and tested. The advantages of a design based on a PLC are simplicity, flexibility. The water level control system using PLC is a simple one. The program was made on an experimental panel with a SIEMENS LOGO! programmable logic controller conducted in the laboratory. PLC are modern technologies that can be used for several control systems such as water

tank level process. SCADA systems are used to monitor and control a plant and equipment in industries. The benefits one can expect from adopting a SCADA system a rich functionality and extensive development facilities. The systems are used to missioncritical industrial processes where reliability and performance are paramount. These systems are used to gather and analyze “real time data”. In today’s world industries can only grow by making themselves advance in technology and by upgrading their machineries and plants. Without human error, the quality of productis better and the cost of production would definitely decrease with no error in quantity required.Water level sensing can be implemented in industrial plants, commercial use and even at home

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BIBLIOGRAPHY:

plc programmable logic controller by HUGH JACK

Practical SCADA for Industry (David Bailey, Edwin Wright)

Process Plant Machinery (Second Edition) by Heinz P. Bloch, Claire Soareswww.marineeng.com/scada . www.modcomp.com/scada/virgina_power.html . www.electronics_x.com/electronic/waste water.htmlwww.modular-scada.co.uk/what -is-scada.htmlwww.electronics.com/power generation/scada.html

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