A PLC (programmable logic controller) can be described as a microcomputer as well as a microcontroller. The both contain the same basic components: an ALU (arithmetic and logic unit), a local memory area, a control section, and the ports of input/output (I/O). Nevertheless, they are typically fewer powerful than a PC. Some common applications of PLC are:
• Handling of chip and wood in the industry of lumber,
• Packaging and filling in the industry of food,
• Material handling and batch processing in the industry of chemical,
• Test and machining stand control,
• Rolling mill and furnace controls in the industry of metal.
PLCs are currently utilized to substitute the controllers of traditional relay-based that were utilized to control industrial processes as PLCs give more flexible alternatives. The options menu that gives to this flexibility comprises:
• The small size PLC which eases the controller locality with the process or the machine being controlled,
• Computer software is user friendly to let the control process specification in the programming standard methods whether FBD, LD, ST, SFC, IL or other modern programming creates for example state diagrams,
• Local area networks networking which lets for control processes remote management through the ports of communication and the hardware interfaces standardization for manufacturer interchangeability.
LD (ladder logic diagrams) is selected in exploring the most efficient technique for the effective resources deployment. LD is a language of graphical according to ladder programming. LD is a method that developed from the wiring diagrams of electrical that were utilized in the car industry for describing schemes of relay control and is currently commonly used to program the present PLCs generation. LDs can be utilized to officially stand for any relay based binary control and provides a smooth transition for engineers of electrical, who before worked with RLL (relay ladder logic) and wiring diagrams of electrical. It is usually an established fact that the selecting task of the correct PLC for an exacting system is a very hard one in the PLC industry. It is for this cause that the processes automation is of such significance. Some of the a lot of parameters that must be considered in selecting a PLC are: the inputs and outputs number, the memory of program, size of data memory, the communication ports number, the instructions number that they support. These parameters are controlled as element of a database. The database efforts to detain most variables, thus enabling an engine selection to perform the most detailed search probable. The estimation of code is utilized to compute the specific database values for attributes of component that can be collected from the program of ladder logic leading to the choice of the suitable component.