MATERIAL COLLECTION THROUGH BAG HOUSE USING PLC
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21-12-2010, 02:58 PM
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Presented By:Moitreyi Sen
BACHELOR OF TECHNOLOGY
APPLIED ELECTRONICS AND INSTRUMENTATION ENGINEERING
MATERIAL COLLECTION THROUGH BAG HOUSE USING PLC
OBJECTIVE OF THE PROJECT :
To develop a logic sequence so as to demonstrate how cement is collected in bag filters using the BAG HOUSE PROCEDURE in a cement industry and hence implement it with Automated Purging Sequence Simulation using Programmable Logic Controller (AllenBradley,Micrologix).
INTRODUCTION TO INDUSTRIAL AUTOMATION
By industrial automation a person will be able to understand the things happening in the modern industry. An industrial can be achieved by utilizing the electrical hardware such as push button switches, emergency stop switch, contactors, timers, limit switches, relays, proximity switches etc. In control process all these actions can be taken manually with direct human involvement.
Hardwired logic control was the first step towards automation. Here the contactors, relays with timers are used for achieving the desired level of automation. But it is very complicated due to bulky and complex wiring.
But after development of microprocessor and microcontroller the process of control and automation becomes very easy. It can be done with understandable wirings due to application of digital logic gates.
WHAT IS AUTOMATION?
Automation (ancient Greek: = self dictated), roboticization or industrial automation or numerical control is the use of control systems such as computers to control industrial machinery and processes, replacing human operators. In the scope of industrialization, it is a step beyond mechanization. Whereas mechanization provided human operators with machinery to assist them with the physical requirements of work, automation greatly reduces the need for human sensory and mental requirements as well. Processes and systems can also be (automated).
Automation is basically the delegation of human control functions to technical equipments. By the implementation of automation following evolutions of productivity can be achieved.
• Higher productivity
• Superior quality of end product
• Efficient usage of energy and raw materials
• Improved safety in working conditions
INTRODUCTION TO PLC
• A programmable logic controller is simply a special computer device used for industrial control systems.
• They are used in many industries such as oil refineries, manufacturing lines, conveyor systems and so on.
• Where ever there is a need to control devices, the PLC provides a flexible way to “softwire” the components together.
• A PLC is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at the inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results.
• PLCs are used in many “real world” applications. If there is industry present, chances are good that there is a PLC present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries you are probably already using them.
The main difference from other computers is that PLC are armored for severe condition (dust, moisture, heat, cold etc) and have the facility for extensive input/output arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the position of complex positioning systems . Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may be external I/O modules attached to a computer network that plugs into the PLC.
PLCs were invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers and drum sequencers.
Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hardwired control panels when production models changed.
The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, disturbed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC- like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.
INTERNAL ARCHITECTURE OF PLC
It consists of a central processing unit containing the system microprocessor, memory, and input/output circuitry. The CPU controls and processes all the operations within the PLC. It is the supplied with a clock with a frequency of typically between 1 and 8 MHz. The frequency determines the operating speed of the PLC and provides the timing and synchronization 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. In the physical sense, a bus is just a number of conductors along which electrical signals can flow. It might be tracks on a printed circuit board or wires in a ribbon cable. The CPU uses the data bus for sending data between the constituent elements, the address bus to send the addresses of locations for accessing stored data and the control bus for signals relating to internal control actions. The system is used for communications between the input and output ports and the I/O unit.
The internal structure of the CPU depends on the microprocessor concerned. In general they have:
• 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.
The buses are the paths used for communication within the PLC. The information is transmitted in binary form, i.e. as a group of bits with a bit being a binary digit 1 or 0, i.e. on/off states. The term word is used for group of bits constituting some information.
Thus a 8 bit word might be binary number 00100110. Each of the bits is communicated simultaneously along its own parallel wire. The system has four buses:
• The data bus carries the data used in the processing carries out by the CPU. A microprocessor termed as being 8-bit has an internal data bus which can handle 8-bit numbers. It can thus perform operations between 8-bit numbers and deliver results as 8-bit values.
• The address bus is used to carry the addresses of memory locations. So that each word can be located can be located in the memory, every memory location is given a distinct address so that they can be located, so each word location is given an address so that data stored at a particular location can be accessed by the CPU either to read data located there or put i.e. write, data there. It is the address bus which carries the information indicating which address is to be accessed. If the address bus consists of 8 lines, the number of 8-bit words, hence number of distinct addresses is 28=256. With 16 address lines, 65536 addresses are possible.
• The control bus carries the signal used by the CPU for control, e.g. to inform memory devices whether they are to receive data from input or output data and to carry timing signals used to synchronize actions.
• The system bus is used for communications between the input or output ports and I/O unit.
There are several memory elements in a PLC system:
• System read-only-memory (ROM) to give permanent storage for the operating system and fixed data used by the CPU.
• Random-access memory(RAM) for the user’s program.
• Random access memory (RAM) for data. This is where information is stored on the status of input and output 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 I/O addresses and the states of those inputs and outputs. Part will be set aside for preset 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. The programs and data in RAM can be changed by the user. All PLCs will have some amount of RAM to store programs and that have been developed by user.
SOURCING AND SINKING
The terms sourcing and sinking are used to describe the way in which dc devices are connected to a PLC. With sourcing, using the conventional current flow direction as from positive to negative, an input device receives current from input module, i.e. the input module is the source of current. If the current flows from output module to output load then the output module is referred to as sourcing.
• SELF TEST – Checks to see if all cards error free, reset watch-dog timer, etc.(A watchdog timer will cause an error, and shut down the PLC if not reset within a short period of time this would indicate that the ladder logic is not being scanned normally).
• INPUT SCAN – Reads input values from the chips in the input card, and copies their values to memory. This makes the PLC operation faster, and avoids cases where an input changes from the start to the end of the program (e.g., an emergency stop). There are special PLC functions that read the inputs directly, and avoid the input tables.
• LOGIC SOLVE/SCAN – Based on the input table in memory, the program is executed 1 step at a time, and outputs are updated. This is the focus of the later sections.
• OUTPUT SCAN – The output table is copied from memory to the output chips. These chips then drive the output devices.
GUIDELINE TO CEMENT ANALYSIS
There are three kinds of process involved cement manufacturing.
Modern plants, four stage preheated kilns with or with out calciner, long dry kiln (no preheater especially in USA). The chart on the following page shows a flow sheet of modern cement plant including an integrated coal preparation plant.