Programmable Logic Controllers - Assignment Example

Programmable Logic Controllers By [Presented to] of Scenario Before programmable logic controllers were created, many industries across the world used other methods to control and manage their processes. PLCs were first designed in 1968 with a design for multiple inputs and outputs. The major purpose of this paper is to analyse different aspects of PLCs in an illustrative manner leading to better understanding. Task-1: Three Kinds of PLCs There are three kinds of PLCs in the form of Unitary, Modular, and Rock Mounted. All these PLCs are different in nature and features and can be used as per the requirement and feasibility. A Unitary PLC contains all the feature of a basic system involved in one basic unit. Major features include power supply, module containing CPU, input module, output module, and direct attachment to the machine they are controlling. The major advantage of Unitary PLC are small and compact, hold each component together, allow portable access, and economic in nature while major disadvantages are little expandability, replacement of the entire unit once a feature fails, and simple and basic outlook (Heath, 2003). It can be used in the car barrier requiring a simple program. The basic example has been highlighted below: On the other hand, Modular PLCs are used as a system of modules that can be used together to build up a system. Major features include power supply, module containing CPU, input module, output module, and other modules to increase the capacity. The advantages of this PLC is it can be expanded to cope up with the changes in hardware and if one feature fails, only that is required to be changed rather than changing the entire PLC. The only disadvantage associated with this PLC is the price that is quite high compared to the Unitary PLCs. However, this is not the severe disadvantage as with high process come high quality and better features. The basic example of modular PLC has been stated below: Another kind of PLC is in the form of Rack Mounted PLC which is very much similar to Modular PLC. This module can be slot together into a rack and communication happens via the rack. The major advantages of rack mounted system are easy to modify and expand, have more input and output sections, and no need to change the entire system if one feature fails. The disadvantages are in the form of high price large amount of space required to assemble the PLC. However, this is not the major disadvantage as it also offers better features and functions required to perform multiple tasks. An example has been presented as follow: Task-2: Switching Voltage and Sensors It needs to be mentioned that the input module converts the voltage level along with preventing voltage to reach the CPU or low level. Input module converts signals from sensors to processor in a direct way. Common voltage levels required by any PLC are 5vDC, 24vDC, and 22Vac. However, the most common voltage for inputs are 5dc, 24dc, 24vac, 110ac, and 220ac (Maher, 2009). There are a thousand of censors that can be used and can be connected to a PLC enabling it to control a typical industrial process. Some of the censors are in the form of limit switches, light curtain, level switches, timers, directional sensors, broken beam sensors, and proximity sensors. Each sensor has different features and can be used as per the requirement and significance (Keller, 2004). Task-3: Switching Voltage and PLC Outputs are usually TTL suggesting they switch from 0.5 voltage to 3.5 voltage. At the same time, PLC offers a number of choices in the form of 120 Vac, 24Vdc, and dry contact outputs. Five devices that can be controlled in an industrial process are in the form of motor control, valves, variable frequency, positioner, and plant control. These are typical output devices commanded by PLCs in industrial processes. Though, there are a number of other output devices but these five are highly preferred in industrial processes. On the other hand, an opto-isolator PLC input protects the input board from short circuits. It also helps in eliminating noises by controlling the voltage/time duration. The purpose of opto-isolator input board is quite relevant in industrial processes as it protects the input board. Task-4: PLC Storing and Executing a Program A PLC stores and executes programs in three simple steps. The first step is to look at each input in terms of determining whether it is on or off. The first step also analyses whether sensors are connected to inputs or not. It records data into the memory that is used in the second step. The second step executes program with one instruction at one point of time. It further stores the execution results to be used in the later step. The third step is to update the status of the output. It updates the outputs based on the inputs used in the first step and in the execution stage. Furthermore, it is important to explain few terms that are associated with the storage and execution of inputs and outputs. The explanations of terms are as follow: CPU- the central processing unit is the electronic circuitry within the computer that carries the specific functions of the computer where majority of functions take place. ALU- arithmetic logic unit is a digital circuit that performs logical operations on integer binary numbers. It is a part of CPU. ROM- read only memory is a storage medium used in computers. It cannot be removed but can only be read and plays a vital role in storing information. RAM- random access memory allows data to be read and written and is one of the most important and common kind of memory used in computers and electronic devices. Register- Register is one of the smallest set of data that are a part of computer processor. Buses-a bus is collection of wires through which data is transmitted to different machines Flags- flag is a pre-defined bit holding a binary value to remember something. The next part of the discussion explains diagram showing how the various parts of a PLC are connected both electrically and mechanically. Reference: John, G (2014) PLC- Computer Marvels. [Online] Available at http://jeugenejohn.hubpages.com/hub/Programmable-Logic-Controller-Computer-Marvels. [Accessed February, 24, 2015]. Task-5: Digital Information Communication and PLC PLC technology is fully capable of transmitting voice, data, and video data through electric supply and can be extended by using local area network and internet connection through electric plugs using PLC adapters. Some of the key descriptions in this regard are as follow: Twisted Pair- twister pair cabling is a form of wiring in which two conductors are joined together for mitigating the impact of electromagnetic interference from wide arrays of external sources. The associated wires carry equal power but opposite signals that is neutralised because of the phase shift. Twister pair of wiring is often associated with the home use, it is also used for LAN installations wiring mainly because it is cheap in terms of the price. The best example of twisted pair wires in terms of the use is in telephone and LAN collection. Additionally, twisted pair mainly ordinary copper wire is also used in internet and phone connection. This form of wire is highly used in the computer industry. The example of this kind of wire has been presented below in a graphical manner. Coaxial Cable- coaxial cable is used to connect electronic devices to aerial. It is also wisely used in connecting computers and PLCs with systems such as Ethernet and other kinds of local area networks. This kind of cable has inner conductor along with concentric conductor made from copper and separated by the layer of insulation. The outer layer is usually grounded and can carry information to a great distance. It needs to be mentioned that data is transferred through the central wire while the outer layer serves as a line to the ground (Gregory, 2004). Both the conductors are parallel in nature and thus are known as coaxial. The graphical illustration has been shown as follow: From the picture, it is very much evident that the copper wire is used as an input while the insulation protects the wire. It is further followed by the copper mesh and outside insulation making it safe in terms of the use. Overall, it can be said that coaxial cable is one of the highly used cables in the computer and entertainment industry helping in delivering high value through the effective amalgamation of inputs and outputs. Fibre Optics- fibre optics is thin glass strands. When light is passed into one end of the strand, it is carried inside the fibre over a long and numerous distances without losing the strength. The light is used to carry digital information at enormous speed and rates. Optic fibres carry large amount of information compared to other copper wires and is not subjected to electromagnetic interference and need to transmit signals. Additionally, many strands can be joined together to give many more channels. It is often seen that computers needing high speed and high data transmission rates use fibre optics to the servers. It can be said that fibre links are one of the safest and fastest wires being used in the computer industry for delivering high speed data and information in a hassle free manner. In today’s time, very communication requires fibre optics allowing network builders to divide their network into several smaller areas and preventing large number of companies and customers to get affected by any outage. Fibre optics offer higher bandwidth required for delivering high speed of communication. Fibre optics is mostly used in many industries mainly because of its reliability and safety. Additionally, it divides networks that further help in enhancing the overall network prospects in the long run. Wireless Networks- wireless network uses wireless data connections for connecting nodes in an effective manner. Wireless networks use radio communication and is often less expensive compared to cables. Wireless LAN is one of the highly preferred wireless connections offering high speed data communication and transfer. Wireless networks are often useful in industrial and companies’ setups offering quality set of data communication. An example has been highlighted below: Task-6: Sequencing System Operated by a Mitsubishi Fx1 PLC The Mitsubishi Fx1 PLC offers a number of communication options that can be connected to other third party products such as bar code readers and printer. The Fx family has a simple programming structure combined with basic and combined instructions. On a general note, Fx devices are small and compact in nature often untraceable when maintenance happens. It is a self management system often helping the engineers to devote time on other maintenance works. Additionally, the Mitsubishi Fx1 is highly used in industrial space mainly because of its usefulness in terms of getting connected to third party products. Possible problems of Mitsubishi Fx1 are in the form of lack of multitasking. It can be used only for calculations and logic solving. Additionally, this PLC is not fully structured but offers reasonable performance. Task-7: Programmable Device to Control Machines and Processes Other programmable devices apart from PLCs are embedded system and industrial control system. Both these systems are used for sharing data and information. An industrial control system is used in industries for data acquisitions. Data are collected from sensors and often executed in a hassle free manner. Major advantages are in the form of hassle free operation and accessibility while major disadvantages are in the form of controlling industrial processes and that too specific ones. On the other hand, embedded system is a computer system including hardware and mechanical parts to control wide arrays of devices. Major advantages of embedded system are low power consumption, small size, and low cost. On the other hand, major disadvantages are in the form of limited processing resources making them hard to use and limited potential to collect and execute data. All these programmable devices are different in nature as compared to PLCs but offer same sort of benefits in a restricted manner that can be assumed as quite useful. Overall, based on the analysis, it can be said that PLCs are very important in delivering, storing, and executing wise arrays of information but its components and features should be analysed well before the final implementation. A number of PLCs may offer wide arrays of benefits and services but can be slow and less feasible in managing numerous data and information. Finally, it can be said that, it is important to understand the basic and standard intricacies of managing and implementing PLCs for better results and outcomes in the industrial processes in the long run. References Gregory K. M (2004), Douglas M. Considine (Ed), Process/Industrial Instruments and Controls Handbook Fifth Edition, McGraw-Hill. Heath, Steve (2003). Embedded systems design. EDN series for design engineers. Oxford Publishers Keller, W (2004) A Functional Chart for Sequential Processes, 14th Annual International Programmable Controllers Conference Proceedings, p. 71-96. Maher, M J. (2009) Real-Time Control and Communications. 18th Annual ESD/SMI International Programmable Controllers Conference Proceedings, p. 431-436. Parr, E. A (2009) Industrial Control Handbook, Industrial Press In Read More