PLC neede of it and the programmable.pptx

plc

1. PROGRAMMABLE LOGIC CONTROLLERS(PLC)

2. DEFINITION OF PLC A digital electronic device that uses a programmable memory to store instructions and to implement specific functions such as logic, sequence, timing, counting and arithmetic to control machines and process. A PLC is a computer designed to work in an industrial environment.

3. MAJOR COMPONENTS OF COMMON PLC SYSTEM

4. MAJOR COMPONENTS OF PLC Contd …. POWER SUPPLY It provides the voltage needed to run the primary PLC components. INPUT MODULES It accepts and converts signals from sensors into a logic signal. OUTPUT MODULES It converts control signal instructions a signal that can be used by actuators. PROGRAMMING DEVICE The programming terminal is used for programming the PLC and monitoring/sequencing PLCs operation.

5. Contd …. PROCESSOR It is the brain of PLC and governs the activities of the entire PLC system. The CPU consists of following blocks: Arithmetic Logic Unit(ALU), Internal memory of CPU, Internal timers, Counters & Flags. The various operations performed are: Scanning I/O bus traffic control, Program execution, Peripheral and External device communication etc. MEMORY It is the component that stores information, programs and data in memory. Types of memories used in PLC are- RAM & ROM.

6. COMPARISON B/W PLC & RELAY It eliminates the hard wiring associated with conventional relay control circuit. It is small and inexpensive compared to equivalent relay based process control. Capable of simulating a hundred relay, timers and counters. Easy to program and install. It can be designed with communication capabilities that allow them to converse with other computer systems or to provide human interfaces.

7. PLC OPERATION SEQUENCE SELF TEST Testing of its own hardware & software for faults. CHECK INPUT STATUS First the PLC takes a look at each I/O to determine if it is on or off. EXECUTE PROGRAM Next the PLC executes the program one instruction at a time. UPDATE OUTPUT STATUS Finally the PLC updates the status of the outpts . It updates the outputs based on which inputs were on during first step.

8. Internal architecture PLC

9. PLC Architecture It consists of a central processing unit (CPU) containing the system microprocessor, memory, and input/output circuitry The CPU controls and processes all the operations within the PLC. It is supplied with a clock with a frequency of typically between 1 and 8 MHz. This frequency determines the operating speed of the PLC and provides the timing and synchronisation for all elements in the system. The information within the PLC is carried by means of digital signals. The internal paths along which digital signals flow are called buses .

10. CPU The internal structure of the CPU depends on the microprocessor concerned. An arithmetic and logic unit (ALU) which is responsible for data manipulation and carrying out arithmetic operations of addition and subtraction and logic operations of AND, OR, NOT and EXCLUSIVE- OR. Memory, termed registers , located within the microprocessor and used to store information involved in program execution. A control unit which is used to control the timing of operations

11. The buses The buses are the paths used for communication within the PLC The system has four buses The data bus The address bus The control bus The system bus

12. Data bus Data bus carries the data in the CPU It has 8 bit internal data bus which handle 8 bit number Example: 11001011 Thus the perform operations between 8 bit number and deliver result as 8 bit data.

13. Address Bus The address bus is used to carry the addresses of memory locations . So that each word can be located in the memory, every memory location is given a unique address. The address bus which carries the information indicating which address is to be accessed. If the address bus consists of 8 lines, the distinct addresses, is 2 8 = 256. With 16 address lines, 65 536 addresses are possible.

14. Control Bus The control bus carries the signals used by the CPU for control, e.g. to inform memory devices whether they are to receive data from an input or output data and to carry timing signals used to synchronise actions.

15. System bus The system bus is used for communications between the input/output ports and the input/output unit

16. Memory System read- only- memory ( ROM) to give permanent storage for the operating system and fixed data used by the CPU. Random-accessmemory (RAM) for the user’s program and data. where information is stored on the status of input and output devices and the values of timers and counters and other internal devices The data RAM is sometimes referred to as a data table or register table . Part of this memory, i.e. a block of addresses, will be set aside for input and output addresses and the states of those inputs and outputs. Part will be set aside for present data and part for storing counter values, timer values, etc. Possibly, as a bolt- on extra module, erasable and programmable read- only- memory (EPROM) for ROMs that can be programmed and then the program made permanent.

17. Memory To prevent the loss of programs when the power supply is switched off, a battery is used in the PLC to maintain the RAM contents for a period of time. After a program has been developed in RAM it may be loaded into an EPROM memory chip, often a bolt-on module to the PLC, and so made permanent. In addition there are temporary buffer stores for the input/output channels

18. PLC PROGRAMMING LANGUAGE PLC programming languages refers to the method by which user communicates information to the PLC. LADDER LOGIC is the oldest programming language for PLC. It is well suited to express Combinational logic. The main ladder logic symbols represent the elements:

19. ADVANTAGES OF PLC Realiability Flexibility in programming and reprogramming. Cost effective for controlling complex systems. Small physical size. High speed of operation. Ability to communicate with computer systems in plant. Ease of maintenance. Reduced space. Energy saving.

20. APPLICATIONS OF PLC Whenever automation is desired the PLCs are best suited to meet the task. PLCs were originally used to substitute the switching relay networks used in industrial applications, but now they can be used to implement other tasks such as timing, delaying counting etc. Some examples of industries using PLCs are: Food/ Beverage Material Handling Robot manufacturing and control Conveyor System etc.

21. . Block Diagram To study of the instrumentation amplifier INSTRUMENTATION AMPLIFIER Transducer Instrumentation amplifier Application Circuit Diagram : R 2 V o ‐V ee ‐V ee R’ +V cc +V cc +V cc I V 1 V 2 R’ R R 2 R 1 R 1 V 2 V 1 ‐ + + ‐A1A1 ‐ +A2A2 Stage 1 Stage 2 ‐V ee Fig3: Analog circuit

22. Pin Diagram :

23. Stage 1: Differential input/output amplifier Stage 2: Inverting amplifier Theory : Instrumentation amplifier is a kind of differential amplifier with additional input buffer stages. The addition of input buffer stages makes it easy to match (impedance matching) the amplifier with the preceding stage. Instrumentation are commonly used in industrial test and measurement application. The instrumentation amplifier also has some useful features like low offset voltage, high CMRR (Common mode rejection ratio), high input resistance, high gain etc. If it’s needed to vary the gain of the instrumentation amplifier then the resistance R is replaced by a suitable potentiometer.

24. Formulae applied: The voltage gain of the complete circuit The overall voltage gain can be controlled by adjustment of R . The common mode signal attenuation for the instrumentation amplifier is that provided by the difference amplifier. This can be maximized by making resistor R 2 adjustable. The dc output voltage level can be controlled if R 2 is connected to an adjustable bias voltage of being directly grounded.

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