Programmable Logic Controller Technology - Assignment Example

PLC Technology affiliation PLC Technology Task Unitary Being the earliest PLC, it s back its origin in 1970’s and is very compact with a unsophisticated design and is the slightest expensive of PLC types on the market. It includes all of the elementary features such as, the CPU and I/O boards and are usually used to run small manufacturing processes or machines that do not need frequent updating and upgrading. Nevertheless a separate power supply is compulsory which can and this has a long time effect on the cycle time of the PLC (Bertrand, 2004). These machines have several advantages like reliability, on the other hand their main shortcoming is that they are non-extendable and as result this limits its ability if the manufacturing processes demand and increment of space. Modular The modular PLC closely resembles the unitary PLC and is in terms of size and the outlook though it is to some extent expensive. This system is composed of 3 basic modules the input, output and CPU with deferent inputs of power sources. Their advantage is allowing a range of modules to slot together to expand the system by usually mounting them on a DIN rail and by merely additional of one unit to another and connecting the processor of the existing unit. It is important to understand that this module is limited in expansion due to the ability of the CPU speed of scanning. In most cases, they are used for small manufacturing process needs but with a option of expansion if processes were to increase in the near future. As mentioned above, it has the capability of expanding when demand rises. On the other hand, they use separate power supplies which are tricky. Moreover, if one component gets damaged, the whole system will be replaced. Rack-mounted The rack mounted PLC is applied large automation processes are essential such as production lines. This is an analogous idea to the modular design. Purchasing this system in the beginning is expensive but is a better long term solution for large processes/ programs. When the system needs updating and changing, it permits slotting of memory cards and process cards any time. In addition to that, it also offers its own power supply for that reason the scan time is tremendously faster and can survive later expansion. The CPU can also be reformed to suit the systems a necessity which permits the user to increase its size when the system is expanding which inhibits the scan cycle time and thus ensures that the system does not slow down. On the other hand, the initial cost of purchasing it is overwhelming. Task 2 The typical switching voltages that can be applied on a typical PLC input is 24v dc supply. Proximity sensor switch The proximity switch is used to sense things when it is moved within the parameters of its range. An instance of this may be with a production line which transports a product on a moving pulley belt. Once the product passes close, the proxy switch an input signal is delivered and its status changed in the PLC. They come in varied ways like the photoelectric sensor, capacitive switch. Another application of the switch is the detection of metal products and operates when a product enters its range. The output signal is produced when a metal object arrives at the magnetic field set up in the switch which causes the checking circuit to function. Limit switch. The limit switch is an electromechanical system that is usually at open state. It comprises of two contacts and a lever arm. When a component put a brake on this lever a signal is produced through the lever and across the two contacts. Application of the devices is during over travel. Say a product the is on transfer pass a certain point which is thought to be dangerous, as a result operating the switch and producing a relay to either increase or reduce power from the motor which is powering the conveyor or transfer bar (Rehg, & Glenn, 2009). Light beam A light beam, also known as a photoelectric sensor, is another type of input. It comprises of a transmitter that transmits an infra- red signal to a reflector that reflects it back. The signal is then reflected at an angle of reflection that enables the receiver to detect it. In case the reflected signal is blocked, the circuit detects this and records appropriately. Use of programming languages In the modern world, PLC’s are linked via PC’s and allow programs to be entered, changed and extended to meet the requirements off the user and the requirements of the processes. There is several software varies marginally conditional on the manufacturer. A good example is the PL7 which is the software whose manufacture is the Schneider/Telemechanique, or S7 consumed by Siemens and RS Logix 500 and has been incorporated by companies like Allen Bradley. Essentially a manufacturer designs a program that is compatible and works well with his PLC. However, due to international conventions, manufacturers have been designing these programs with a common programming language that can easily be used universally. Task 3 Some of the devices that can be controlled are, flow control, where air or fluid can is monitored and regulated by progressively closing or opening a shut valve in relative to the values that are have been keyed in the program and the actual flow rate value. Photo cells are light chargeable cells which are automatically activated when power goes off. These cells are controlled by PLC’s that connect the cell to mains circuit. When electricity comes back they are automatically switched off. Proximity sensors and switches are used to detect things that are near and trigger automation of signals. They are mostly used to in parking for controlling the extent to which a car should part to the walls of the company. When the car goes to close to the walls, the proximity sensor triggers an alarm. Take a simple limit switch which under constant supply of 24v direct current. Once the limit switch is made the 24v signal will be relayed at the PLC which is managed and updates the status of the related contact inside the program. The Opto-isolator is an significant electronic device that is mounted with the motherboard of the CPU and is used to protect and prevent the CPU becoming damaged from exterior electrical sources. It achieves this purpose by isolating the CPU that is brought about by the interaction of two components, L.E.D and transistor. Signals are continuously transmitted to the L.E.D which is then receipted up by the transistor. This permits the power supply to be switched in absence any electrical association but just by means of the light source. Task 4 The CPU works by scanning functions within the PLC. It essentially scans the PLC to tart read and govern the status of inputs from devices such as various sensors and switches. After scanning, it will update all the components which are obsolete. As long as the program diagnostics are fulfilled then the output devices will be turned on or off. It is however important to understand that the scanning process affects the speed in which the program is performed but though it is directly proportional to the length of the program the processor speed. Scanning speeds are usually measured in nanoseconds. i. CPU The Central Processing unit within a PLC accomplishes the actions of reading, controlling and executing command and is mostly referred to as the brain of the computer. ii. ALU The Arithmetic Logic Unit is as unit that performs mathematical computations like addition, subtraction, division and multiplication. iii. ROM Read Only Memory is a unit that contains pre-written programs that are essential for working of the computer. It is a read only memory meaning that it cannot be reprogrammed. iv. RAM Random Access Memory is a unit that enables efficient working of the PLC by storing temporary memory in the runtime environment. v. Registers It is a place designed to store memory on temporary basis and once the stored memory had been manipulated, it is taken to another location for further processing. vi. Buses These are connections especially wires used to carry signals within the PLC. vii. Flags These are predefined bits or data in a computer. Task5 i. Twisted pair Twisted-pair cable is the most common type of cabling one can come across in most Local Area Networks (LAN). This is a pair of wires that forms a circuit that can transmit data from one computer to another. The pairs are twisted to offer protection against crosstalk which is produced by neighboring pairs. The connected wire produce magnetic effects owing to the current they are currying. Sometimes, this field creates interference can interfere with signals on adjacent wires. To remove this, the two pairs of wires carry current in different direction so that the magnetic fields generated undergo destructive interference. This process is known as cancellation. They are of two types, the Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP). In the current world, the unshielded twisted-pair cable dominates networking media. Composition of the unshielded twisted-pair is four pairs of thin twisted, copper wires enclosed in color-coded plastic insulation. Twisted pair are cheap and readily available however they are prone to signal distortion hence prone to errors. ii. Coaxial cable They are normally used for Push buttons, photo cells, limit switches among others. It has an inner coating made of Faraday shield which minimizes noise hence reducing error rate. Signal loss is directly proportional to the frequency of the signal therefore they are inefficient in carrying high frequency signals. iii. Fiber optics Optical Fiber cables use optical fibers that transmit digital data signals in the form of modulated pulses of light. An optical fiber is made up of an very thin cylinder of glass, called the core, enclosed by a concentric layer of glass, identified as the cladding. In a given cable, there are two fibers—which whose sole functions are transmission and reception of signals respectively. The composition of the core also can be an optical-quality clear plastic, and the cladding can also be composed of any gel that reflects signals back into the fiber to lessen signal loss. They allow superfast transmission of signal while on the other hand they components associated with the cables are expensive. iv. Wireless Networks It is an interconnection of computer that does not involve physical connections with Ethernet cables but via routers. One advantage is computers do not need to be connected to each other. Disadvantages is signals grow weak with distance and boosters have to be used to boost them. Task 6 i. To Binary ii. iii. iv. Task 7 The Mistubish Fx PLC control two single-acting electrically triggered air-filled pilot valves, whose motion in turn control two air-filled pistons. Working of the PLC consists of several steps as outlined below: input, output and transfer condition. A correct input produces an output which becomes the input to the next phase of the process. In other words, the output is turned on or off depending on the input. With an ON or OFF state in the output, a transfer condition is generated which is then connected to the input condition of the sequential state. If the input is correct, the sequence repeats itself to the next stage until the complete machine cycle is completed. Task 8 The Leviton switch is used to control indoor and outdoor lighting. One advantage is that it helps in saving energy while on the other hand its footprint is larger than the smaller size it is likely to replace. The thermocouple; they are programmed to automatically control temperatures in industries. When temperatures rise above a certain level the switch on the fans and when temperature drops to a certain level, the switch off the fan thus maintaining a steady temperature. Thermocouple are very effective for they can be used to measure extremely high temperatures of up to26000 C. on the other hand, they are complex system to install and in most cases are potential to errors. References Bertrand, R. (2004). Programmerable logic controller: basic principle using the programming software. New York: Delmar Publishers. Rehg, J., A., & Glenn, J., S. (2009). Programmerable logic controller. New York: Pearson Prentice Hall. Read More