PLC BASED AUTOMATION   by  santosh kr Singh, Dharmbir  Prasad, Gautam agarwal,   Jay s parikh, Mihir parikh,Prithvi Ramdyani, Arnab datta, & suman chatterjee .They are all group of  engineers in R&D department of Supreme & Co.Pvt.Ltd. And this "Automation" project directly supervised by me (Harish Agarwal).

Bibliography-

Santosh Kumar Singh

Pursuing M.Tech in Power System Engineering and passed Electrical Engineering from WBUT in 2009. He is a member of IET,UK. He was a participant of student pavilion of Elecrama-2008 with a project on Harmonics. His area of research is on power system quality like harmonics, transient stability, power automation using SCADA and optical fiber system. He Supreme & Co. has published many research papers in this filed. Right now he is working in the R&D department of kolkata, India.


Dharmbir Prasad

Pursuing M.Tech in Power System Engineering and passed Electrical Engineering from WBUT in 2009. He is a member of IET,UK. He was a participant of student pavilion of Elecrama-2008 with a project on Harmonics. His area of research is on power system quality like harmonics, transient stability, power automation using SCADA and optical fiber system. He has published many research papers in this filed. Right now he is working in the R&D department of Supreme & Co. kolkata, India.

Gautam Agarwal

He is  a student of fourth year Electrical Engineering of Visvesvaraya University Bangalore. He is an intern Research Engineer(R&D) of Supreme & Co., his area of research is on power system automation.

 

Mihir Parikh

He is  a student of fourth year Electrical Engineering of Visvesvaraya University Bangalore. He is an intern Research Engineer(R&D) of Supreme & Co., his area of research is on power system automation.

 

 

Prithvi Ramadhyani

He is  a student of fourth year Mechanical Engineering of Visvesvaraya University Bangalore. He is an intern Research Engineer(R&D) of Supreme & Co., his area of research is on power system automation.

 

Jay S Parikh

He is  a student of fourth year Electrical Engineering of Visvesvaraya University Bangalore. He is an intern Research Engineer(R&D) of Supreme & Co., his area of research is on power system automation.

 

Arnab Datta
He is a Master of Computer Application with more than ten years of experience in IT industry. 

 

 

 

Suman Chatterjee

He is Diploma in Mechanical Engineering with 20 years of experience in various mechanical engineering filed.

                                          INTRODUCTION  ------ PLC BASED INDUSTRIAL AUTOMATION(PART-II)

Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. Many control tasks were performed by contactors, control relays, and other electromechanical devices. This is often referred to as hard-wired control. Circuit diagrams had to be designed, electrical components specified and installed, and wiring lists created. Electricians would then wire the components necessary to perform a specific task. If an error was made, the wires had to be reconnected correctly. A change in function or system expansion required extensive component changes and rewiring.

     It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most recent revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls.

A programmable logic controller (PLC) or programmable controller is a digital computer used for automating electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines, such as packaging and semiconductor machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatilememory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.

Advantage of using  PLC:

PLCs have been gaining popularity on the factory floor and will probably remain Predominant for some time to come. Most of this is because of the advantages they offer includes-

  • Cost effective for controlling complex systems.
  • Flexible and can be reapplied to control other systems quickly and easily.
  • Computational abilities allow more sophisticated control.
  • Trouble shooting aids make programming easier and reduce downtime
  • Reliable components make these likely to operate for years before failure.
  • Smaller physical size than hard-wire solutions
  • Easier and faster to make changes
  • PLCs have integrated diagnostics and override functions
  • Diagnostics are centrally available
  • Applications can be immediately documented.
  • Applications can be duplicated faster and less expensively.

Major components of a common PLC:             

  1.  POWER SUPPLY(PS)
  2. CENTRAL PROCESSING UNIT OR MICRO-PROCESSOR (CPU)
  3. SIGNAL MODULES (SM), DIGITAL INPUT (DI), DIGITAL OUTPUT(DO), ANALOG INPUT(AI), ANALOG OUTPUT(AO),
  4. COMMUNICATION INTERFACE (CI)

 

Basic  PLC  Operation:

The basic elements of a PLC include input modules or points, a central processing unit (CPU), output modules or points, and a programming device. The type of input modules or points used by a PLC depends upon the types of input devices used. Some input modules or points respond to digital inputs, also called discrete inputs, which are either on or off. Other modules or inputs respond to analog signals. These analog signals represent machine or process conditions as a range of voltage or current values. The primary function of a PLC’s input circuitry is to convert the signals provided by these various switches and sensors into logic signals that can be used by the CPU.

The CPU evaluates the status of inputs, outputs, and other variables as it executes a stored program. The CPU then sends signals to update the status of outputs. Output modules convert control signals from the CPU into digital or analog values that can be used to control various output devices. The programming device is used to enter or change the PLC’s Program or to monitor or change stored values. Once entered, the program and associated variables are stored in the CPU. In addition to these basic elements, a PLC system may also incorporate an operator interface device to simplify monitoring of the machine or process.

 

Operation of PLC with various field devices.

In the simple example shown below, pushbuttons (sensors) connected to PLC inputs are used to start and stop a motor connected to a PLC output through a motor starter (actuator). No programming device or operator interface are shown in this simple example.

Programming:

A program consists of one or more instructions that accomplish a task.Programming a PLC is simply constructing a set of instructions. Therways to look at a program such as ladder logic, statement lists, or function blocke are several diagrams.

Ladder logic programming

biggest transition from relay control panels to PLCs was the transition from the hard wired relay logic to logic defined by user program. In order to allow established relay logic users to program the PLC, a visual programming language that looks like a relay control panel was created. This visual programming language is called “Ladder Logic”.

 Statement List:

A statement list (STL) provides another view of a set of instructions.

Network 1   

                    LD              10.0

                    A                 10.1

                  =                   00.0

Network 2

         LD                         10.4

           0                           10.5

          =                           00.1

Function Block Diagrams

Function Block Diagrams (FBD) provides another view of a set of instructions.

Network 1

              10.0                           

               10.1       and      00.0

Network 2

              10.4

                10.5      or 00.1

 

Number Systems:

Because a PLC is a computer, it stores information in the form of on or off conditions (1 or 0), referred to as bits. Sometimes bits are used individually and sometimes they are used to represent numerical values. Understanding how these bits can be used to represent numerical values requires an understanding of the binary number system.

Decimal System In order to understand the binary number system, it is first useful to recall some of the basics of the decimal number system. All number systems have the same three characteristics: digits, base, weight. For example, the decimal system has the following characteristics:

Ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Base 1 0

Weights Powers of base 10 (1, 10, 100, 1000, ...)

Binary System The binary system has the following characteristics:

Weights Powers of base 2 (1, 2, 4, 8, 16 ...)

The binary system has a base of 2 and uses only two characters, 1 and 0.

Bits, Bytes, and Words Each position in a binary number is called a bit. The number of bits used to represent numbers varies with the device. However, instructions and data are usually grouped in bytes and eight bits make up one byte. Two bytes, or 16 bits, make up one word.

Logic 0, Logic 1 While PLCs are capable of sensing and generating analog values, programmable controllers internally use signals that are on or off. These on and off conditions correspond to the binary values 1 and 0. For example, a binary 0, also called logic 0, can be used to indicate that a switch is off, and a binary 1 (logic 1) can be used to indicate that a switch is on.

 Terminology

Developing an understanding of PLCs requires learning some basic terminology. This section provides an overview of commonly used PLC terms, beginning with the terms sensor and actuator. Sensors are devices that convert a physical condition into an electrical signal for use by a controller, such as a PLC. Sensors are connected to the input of a PLC. A pushbutton is one example of a sensor that is often connected to a PLC input. An electrical signal indicating the condition (open or closed) of the pushbutton contacts is sent from the pushbutton to the PLC. Actuators are devices that convert an electrical signal from a controller, such as a PLC, into a physical condition. Actuators are connected to the PLC output. A motor starter is one example of an actuator that is often connected to a PLC output. Depending on the status of the PLC output, the motor starter either provides power to the motor or prevents power from flowing to the motor.

Discrete Inputs and Outputs Discrete inputs and outputs, also referred to as digital inputs and outputs, are either on or off. Pushbuttons, toggle switches, limit switches, proximity switches, and relay contacts are examples of devices often connected to PLC discrete inputs. Solenoids, relay and contactor coils, and indicator lamps are examples of devices often connected to PLC discrete outputs. In the on condition, a discrete input or output is represented internal to the PLC as a logic 1. In the off condition, a discrete input or output is represented as a logic 0. Analog Inputs and Outputs Analog inputs and outputs are continuous, variable signals. Typical analog signals vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts.

Remote terminal Units (RTU) : Remote terminal units are distributed through network device group, centralized by PLC control and communicated with similar protocol through serial bus in IEC fieldbus RS485 standards. These networks, often referred to as “data highways”, utilize twisted shielded-pair to carry high speed. Communications data between the various Controller and RTUs microprocessor - based devices connected to the network.

PLC Memory Architecture:

logic scan when the output modules get updated to this previously stored information. These status areas of memory are always available for user monitoring and use

1. System memory

This memory is reserved for program data manipulation. When timers, counters, math, and/or data functions are available, an area of memory must be set aside for data storage. The data storage portion of memory is allocated for storage of such items as timer or counter preset and accumulated values, math instruction data and results, and miscellaneous data and information which will be sued by any data manipulation functions programmed in the user memory area It’s placed in RAM.

2. User memory

This memory is allocated to the storage of the user program. It is the memory area that the executive program instructs the microprocessor to examine or “scan” to find the user instructions. The user program are may be subdivided if the processor allocates a portion of this memory area for the storage of ASCII messages, subroutine programs, or other special programming functions or routines. It’s placed in RAM.

3. Stack memory

This memory is served for storage of stack pointer index in order to execute in subroutine program. It’s placed in RAM.

4. I/O memory

It’s the memory that can be referred to I/O statuses in order to connect with I/O devices. Whenever the executive program instructs the microprocessor to read the current statuses of the inputs to the PLC, it stores this information in the input status or image area. As the executive instructs the microprocessor to scan the user program and interpret the user commands, various output device statuses are generated.

Some of the industrial applications of PLC


1. on/off of lamp

2. Start/ stop of a Motor

3. On/ off a Lamp using buttons

4. Combination of Switches to on a Switch

5. on/off a Pump

6. Flashing of Lamp

7. Auto on/off Door Lamp

8. Traffic Signal

9. Door Bell Alarm & Glass Break Detector

10. Bottle Counting & Rejection

11. Car Entry through Gate

12. Security System of a Car

13. Car Garage

14. Monitor of LED in Forward & Reverse direction

15. Push Button in Toggle Mode

16. Product Testing

17. Thumb Wheel Application

18. Auto door opening with Access Code

19. Staircase Lighting System

20. Opening of Bridge

21. Vendor & Washing Machine Application

22. Film Shooting

23. Paint Industry

24. Orientation Testing Application

25. RAM Press Application

26. Tank Filling Application

27. Auto Door Opening

28. Powder Application

29. Semi Drill of a job

30. Filling and Labeling of a Bottle

31. Lubrication Application

32. Alarm Annunciator

33. Chocolate Industry

34. Washing Plant

35. Lift Application

36. Real Time Clock Application

37. Man Machine Interface & PLC interface

38. Drive & PLC Interface

39. PLCs in Substation Automation and SCADA

      I. Remote Terminal Unit emulation and replacement

     II. Protection and Control

     III. Automatic Switching

     IV. Voltage Regulation Management

      V. Transformation Management

     VI. Automation System Diagnostics

    VII. Maintenance and Safety

  VIII. Station HMI – Graphical User Interface

     IX. Remote Control

      X. Demand Control

     XI. Synch Check and generator Synchronization

The PLC-based model on display has been made by the engineering team at Supreme & Co. Pvt. Ltd. and is one of the “Proofs of Concept” for the myriad of automation solutions the company is looking to provide in the near future.

In this model, the objective is the glue gritting of helical wires without the use of manpower thereby eliminating the possibility of human errors. The model uses four electromagnetic relays and associated pneumatic valves operated by a PLC to perform the required operation on the helical wire. A pneumatic plunger driven by a compressor conveys linear motion to the helical wire. The force and the timing of the plunger are controlled through two electromagnetic relays that control the air pressure through two corresponding valves. The flow timings of the glue and the grit on the remaining valves are also controlled by the PLC and are synchronized to match the movement of the helical wire. All the operations can be controlled precisely and conveniently through programming on the PLC.

Automatic room light control using PLC:  

Our WIP projects also include an Automatic lighting system that requires no switches, i.e. automatic switching on/off of lights as per the presence of people in the room. IR sensors are used to detect entry/exit of people into the room and the circuit additionally maintains a count of the number of people in the room at any given time. The sensors are strategically placed to differentiate between entry and exit of the people. Depending on the number of people passing through the door the counter goes up/down and stores the corresponding value in the register which is referred to by the comparator which controls the tripping of the lighting circuit accordingly. The light will come on as soon as the first person enters the room and does not switch off until and unless the counter value drops to 0.

To know more about PLC BASED AUTOMATION please click the link below:

PLC Automation