module 1.pptx
- 1. PLC AND SCADA Subject code: 18MT61
- 2. Syllabus what is A PLC, Technical Definition of PLC, What are its advantages, characteristics functions of A PLC, Chronological Evolution of PLC, Types of PLC, Unitary PLC, Modular PLC, Small PLC, Medium PLC, Large PLC, Block Diagram of PLC: Input/output (I/O) section, Processor Section, Power supply, Memory central Processing Unit: Processor Software / Executive Software, Multi asking, Languages, Ladder Language.
- 3. WHAT IS PLC PLC is a solid state/ computerised industrial controller that performs discrete or sequential logic in a factory environment. It was originally developed to replace mechanical relays, timers and counters. Used to successfully execute complicated control operations in a plant. A sequence of instructions is programmed by the user to the PLC memory and when the programme is executed the controller operates the system to correct operating specifications. The PLC was introduced in late 1960s
- 4. Today PLC is used as a stand alone control or a part of a Complex Computer Integrated Manufacturing System. PLC may also provide an interface between a machine and robots or a machine and colour graphics which are known as Human Machine Interface (HMI). PLC is important in the world of industrial automation.
- 5. Technical Defination Of PLC Is currently defined by NEMA (National Electrical Manufacturers Association) as a “Digital electronic Device that uses a programmable memory to store instructions and to implement the specific functions such as logic, sequence, timing, counting and arithmetic operations to control machine and processes”.
- 6. History and Origin: • •Developed to replace relays in the late 1960s • •PLC began in the 1970s, and has become the most • common choice manufacturing for controls. • •The PLC was invented in response to the needs of • the American automotive manufacturing industry • (primarily General motors). • •Costs dropped and became popular by 1980s • • Now used in many industrial designs
- 7. PLC Advantages Faster Scan time Intelligent I/O High speed Counters Supervised Control capability Reliability in operation Flexibility in programming and reprogramming in a plant Cost effective for controlling complex systems Flexibility in Control techniques Minimum Maintainance Small physical size Superior computational capabilities to execute complex control techniques ASCII message handling capablity
- 8. Ability to communicate with computer systems in a plant. Programmable troubleshooting aids which reduces the downtime.
- 9. PLC DISADVANTAGES There's too much work required in connecting wires. It is difficult to find errors. Skillful workers are required. There’s difficulty with replacements. PLC devices are proprietary, which means that parts and software from one manufacturer can’t easily be used in combination with parts of another manufacturer, which limits the design and cost options.
- 10. PLC APPLICATIONS • PLC’s are generally used in industries for controlling heavy machinery and processes like conveyor system, CNC machines etc. • PLC usage can also be observed in day to day life. For eg : automatic washing machines, cars, video cameras etc. • PLC has it’s applications in almost every automatic machine.
- 11. COMPONENTS OF PLC 1 . Processor. 2. Memory unit . 3. Power supply. 4. I/O Modules. 5. Programming device.
- 12. Characteristics of PLC PLC offers certain characteristic functions that make it advantageous in an industrial environment. It is superior in modern industrial control and communication. Some of the major characteristic functions of PLC are: 1. It is field programmable by the User: It allows the user to modify the programs as per the requirements of a plant without having it to send the unit back to the manufacturer for this purpose.
- 13. 2. It contains the programmed functions: PLCs contain at least logic, timing, counting and memory functions that the user can access through some kind of control oriented programming language. 3. It scans memory, inputs and outputs (I/O) in a predetermined manner. 4. It provides error checking and diagnostics. A PLC will periodically carry out internal tests of its memory, processor and I/O systems through in built program execution to ensure what it is doing to the machine or system, against what it was programmed to do.
- 14. 5. A PLC can provide some form of monitoring capabilities either through indicating lamps that shows the status of inputs and outputs or by an external device that can display the program execution status. 6. It is packaged in such a way that it can withstand the temperature, humidity, vibration and noise found in most factory environments. 7. A PLC can be effectively designed for a wide variety of control tasks, although it can also be dedicated only for a particular task.
- 19. TYPES OF PLC PLCs are of two types: 1. Unitary PLCs 2. Modular PLCs. 1. Unitary PLC: Unitary PLC has a power supply, a CPU and a limited number of inputs and outputs. It has 20 inputs- 12 outputs, 32 I/O It is sometimes called “shoebox type”. It is mainly used for the control of a small system.
- 21. Unitary PLC
- 22. 2. Modular PLC: A modular PLC is one that it can be constructed using separate modules of power supply, CPU, inputs, outputs, timers, counters, ADC, DAC, expansion modules. These modular PLCs are sometimes called “rack mounted type PLC”. Modular PLCs can be sub-divided into the following types a) Small PLC b) Medium PLC c) Large PLC
- 23. Modular PLC
- 26. a) Small PLC: PLC having less than 100 inputs and outputs are designated as small PLCs. Out of the I/Os, 20 inputs and 12 outputs are mounted locally within the processor. Additional I/Os can be added through remote I/O racks to accommodate the extra inputs and outputs. These PLCs generally have a memory from 2KB to 10KB to store the users logic program.
- 27. b) Medium PLC: These have extended instructions sets that include mathematical functions, file functions, PID process control etc. These PLC can have between 4000 to 8000 inputs and outputs. They are also made to support wide variety of special modules such as ASCII communication modules, BASIC programming modules, 16 bit multiplexing modules, analog input and output modules (both voltage and current), communication modules.
- 28. c) Large PLC The purpose of introducing large PLC was to provide enough memory space and I/O for complete factory automation. Major Disadvantage: Whole Factory may collapse if the PLC starts malfunctioning. Distributed Control: Introducing this enables to use the LAN , where the small or medium PLCs are connected together through an appropriate network. Entire factory is brought under the control of a number of PLCs, but failure in one system will not disturb any other system.
- 29. PLC SYSTEM
- 32. Block Diagram of PLC PLC has three basic sections namely 1) I/O section 2)Processor Section 3) Program loader/monitor section The input section converters convert the field signals to logic level signals that the PLC’s processor can read directly. The processor section reads these inputs, processes the signals executing the program and prepare the output signals. The output section converts the logic level output signals coming from the processor section into high level signals and releases the signals for various field devices. The program loader is to enter the user’s program into the memory or change it and to monitor the execution of the program.
- 33. I/O section The input output section establish the interfacing between the real world outside the PLC and the digital arena inside the PLC. The signals from the machines or instruments of a system are received through the input section by a PLC. After processing the output signals are transmitted to the machines or the instruments for the desired control action through the output section. The tasks of the I/O section can be classified as: 1. Conditioning 2. Isolation 3) termination 4) Indication
- 37. The field signal is 220V or 440 V. PLC can support a voltage of 0-10 volts, the field signal has to be conditioned before it is applied to the PLC. To protect the PLC from any incoming surges from the field, isolating devices such as transformers or an opto-isolator are used. The I/O modules provides a proper terminal. It indicates the status of the I/O terminal, i.e when the voltage is off the status indicator is off.
- 38. Processor Section This section consists of four major elements. 1.) Power supply 2.) Memory 3.) CPU 4.) I/O interface 1) Power Supply: Basic function of the power supply is to supply conditioned power to the components of a PLC. The power supply is one of the most critical components of the PLC for two reasons: 1. It is typically non redundant. Hence failure of PLC power supply can cause entire control system to fail. 2. It contains high voltage components. Hence an insulation failure can be a serious potential for injury or fire.
- 39. The following guidelines should be followed when choosing the power supply of a PLC: 1) The power supply should be packed properly, so that the heat generated by the power supply can be dissipated in order to prevent overheating. This increases reliability. The power supply should be tested for temperature and electrical insulation by a proper certification agency. The power supply should meet at least one reputable standard for noise Immunity. Suitable redundancy will increase reliability.
- 41. 2. Memory Two types of memory in a PLC: i) volatile memory ii) non volatile memory. Non volatile memories: are generally used for storing users programs so that they are preserved during power cuts. The non volatile memory in a PLC uses some form of error checking to ensure that memory has not changed. To ensure to have a safe execution of the users programs this error checking should also be done while PLC is controlling a machine or a process.
- 42. Different types of memory that are generally used in a PLC are as follows. 1. Battery backed up CMOS RAM : This is the probably the most widely used type of memory. CMOS variety consumes such a small amount of power that a small battery will retain memory during the power losses. The battery used vary from short life primary cells (alkaline or Hg) which require periodic replacement after 6 months to a year. To a long life battery which may last up to 10 years to rechargeable secondary cells.
- 43. 2. EPROM Memory: Electrically Programmable Read only Memory is programmed using electrical pulses. Can be erased by exposing the circuit to UV light also called UV-EPROM. 3. EEPROM Memory: Similar to EPROM Memory. It can also be erased using electrical pulses. In some PLC’s use of EEPROM only alleviates the need of an UV light source. In other PLC’s the EEPROM is the only type of memory used. This allows the flexibility of reprogramming.
- 44. Four sections memory is subdivided: Executive memory, internal RAM, user memory and I/O image memory. The executive memory holds executive software. User memory is meant for user program storage
- 45. 3. CPU The flexibility of a PLC is dependent on : i) How CPU is constructed ii) Overall speed of the PLC The speed is expressed in terms of how fst the PLC will scan a given amount of memory. This measure is called scan rate. It is expressed in milliseconds per thousand words of memory.
- 47. 1. Processor: Processor is the central processing unit (CPU) of the programmable controller, it executes the various logic sequencing functions by operating on the PLC inputs to determine the appropriate output signals. The CPU consists of one or more microprocessors similar to that of PCs and other data processing equipment but are designed to facilitate I/O transactions with different ranges with corresponding clock speed.
- 48. Consists of a microprocessor for implementing the logic and controlling the communications among the modulus. Designed, so the desired circuit can be entered in relay ladder logic form. The processor accepts the input data from various sensing devices, executes the stored user program and sends appropriate output commands to control devices.
- 49. 2. Memory: Memory unit is connected to the CPU, which contains the programs of logic, sequencing and I/O operations . It also holds data files associated with these programs, Including I/O stations bits, counter and timer constants, and other variable and parameter values. This memory unit is referred to as the user or application memory because its contents are entered by the user and also directs the execution of control program and coordinates I/O operations with the aid of system memory.
- 50. 3. Power Supply: A power supply of 120v alternating current(ac) is typically used to drive the PLC (some units operate on 240 v ac). The power supply converts the 120v ac into direct current (dc) voltages of ±5V. These low voltages are used to operate equipment that many have much higher voltage and power ratings than the PLC itself. The power supply often includes a battery backup that switches in automatically in the event of an external power source failure.
- 51. Supplies DC power to other modules that plug into the rack. In large PLC systems, this power supply doe not normally supply power to the field devices. In small and micro PLC systems , the power supply is also used to power field devices.`
- 52. 4. I/O Modulus: The input/output module provides the connections to the industrial equipment or process that is not to be controlled. Inputs to the controller are signals from limit-switches , pushbuttons, sensors , and other on/off devices. Outputs from the controller are on/off signals to operate motors, valves, and other devices required to actuate the process. Many PLCs are capable of accepting continuous signals from
- 53. Forms the interface by which input field devices are connected to the controller. The terms “field” and “real world” are used to distinguish actual external devices that exist and must be physically wired into the system.
- 54. Forms the interface by which output field devices are connected to the controller. PLCs employ an optical isolator which uses light to electrically isolate the internal components from the input and output terminals.
- 55. 5. Programming Device: The PLC is programmed by means of a programming device. The programming device is usually detachable from the PLC cabinet so that it can be shared among different controllers. Different PLC manufacturers provide different devices , ranging from simple teach pendant type devices , similar to those used in robotics, to special PLC programming keyboards and CRT displays. PCs and laptops now widely used for programming a much faster and a PC / laptop are also smaller now.
- 56. The software allows users to create , edit .document, store and trouble shoot programs . The personal computer communicates with the plc processor via serial or parallel data communications link
- 57. Hand – held programming devices are sometimes used to program small PLCs. They are compact, inexpensive and easily to use, but are not able To display as much logic on screen as a computer monitor. Hand-held units are often used on the factory floor for trouble shooting, modifying programs and transferring programs to multiple machines.
- 58. Languages Variables: These are the way in which the language allows the user to access the I/O internal data. On line s. OFF line: On line language is the one that can be programmed interactively with the PLC. OFF line: Requires that the program be generated separately then downloaded to PLC. Flow Control: How easy to take decisions and to control the program execution. Maintainability: How easy the language is to debug, modify and teach to others.
- 59. Functions: Some language provide minimum set of logic, timing , counting and memory functions. Speed: Some language takes a longer time to execute than others. Choosing a slow but powerful language in time critical applications can make programming much more difficult than using a fast but simple language. EFFECIENCY: This is the measure of how much memory is required for a language to implement a given function.
- 60. Ladder Language Electrical ladder diagram Relay logic Power flow through the ladder diagram Program is fast Readable program for sequence control
- 61. Multi Tasking Some PLC can execute multiple tasks within a single processor. Two forms of multi tasking: Time driven and Event Driven Time Driven: The user writes programs and assigns a separate I/O for each task. The user may be then allowed to configure the processor to run each task at periodic time intervals. Event Driven: In the Event driven multitasking user defines a particular event that causes each task to run. Some multitasking systems allows any task to access any variable such as an I/O point.
- 62. Configuration process typically consists of: Assigning the I/O points to particular I/O racks. Telling the processor how much memory I/O it has. Assigning specific memory for tasks. Determining the fatal and non fatal faults. Assigning many other items interactively on a program loader. Not all PLC can be configured, but the processor can enhance the efficiency of the PLC if it can be configured.
- 65. Executive software is a program that the PLC manufacturer will provide internal to the PLC, which executes the user program. Determines what functions are available to the users program, how the program is solved, I/O is serviced, what the PLC does during power up, down and fault conditions.