PLC is designed to replace a circuit relay sequential in a control system. In addition to programmable, this tool can also be controlled, and operated by people who do not have knowledge in computer operation in particular.
PLC stands for programmable logic controller, which has the following meaning:
1.Programmable demonstrate ability in terms of memory to store programs that have been made that easily altered function or usefulness.
2.Logic demonstrate the ability to process input in the arithmetic and logic (ALU), which compares the operation, add, multiply, divide, subtract, negation, AND, OR, and so forth.
3.Controller demonstrate the ability to control and manage the process to produce the desired output.
The basic elements of a PLC consists of a Power supply, Programming Console, Memory, CPU, input modules, output modules. following we describe each of these elements.
Power supply is used to provide power supply to all parts of the PLC (including CPU, memory, etc.). Most PLC work on the power supply 24 VDC or 220 VAC.
Programming Console is a programming panel in which there RAM (Random Access Memory) that functions as a semi-permanent storage in a program that was created or modified. Programs written to the console must be in the form of mnemonic. This device can be connected directly to the CPU by using a cable that can be installed ekstention and removed at any time.
Memory is a component for storing the program, To the PLC will work as expected then needed a program to run it. The program should be stored in a certain way so that the PLC can access commands according to the instructions. One also needed to store data temporarily during the implementation of the program.
CPU (Central Processing Unit) is the central data processor and controller of the entire work system PLC. Process conducted by the CPU and other international control of all operations, cultivate existing programs in the memory, as well as manage communications between the input-output, memory and the CPU through the BUS system. CPU also serves to execute and process the functions desired by the program that have been determined. Engineering and environmental consultants SSI has devised a number of emergency projects to assist the municipalities of the southern Cape coastal belt, in light of the severe drought that the area is experiencing.
SSI communications manager Robin Hayes says that during December, tourists flood the region, swelling the resident population by up to five times, exacerbating the existing critical shortage of water.
SSI water sector head Francis Gibbons says that, in Sedgefield, the company specified a 1Ml/day mobile desalination reverse-osmosis plant, together with an upgraded membrane bioreactor wastewater treatment works (WWTW) that enables the indirect reuse of final effluent. New boreholes have also been installed to augment ground and surface water supplies.
SSI’s medium term solution for Knysna and George also involves indirect effluent reuse, where final WWTW effluent is polished by an ultrafiltration process and then pumped into the towns’ storage dams where it combines with fresh water from the rivers.