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A PLC consists of 2 basic sections: the CPU and the I / O system. The PLC consists of two basic sections. The processor and memory system will further break up the CPU which controls all PLC activities. The input / output system is interface between the CPU and input and output / checkable devices (outputs) connected to a field device ( e.g. switches, sensors).
The input module purpose is to transform income signals and send these into a central control unit, which can be processed through the PLC. An output module does the reverse job. In conjunction with the program stored in the memory, the PLC signal will become signal acceptable for the actuators.
The CPU uses its input interfaces to “read” input data from connected field devices, then “runs” or executes the control program saved in the memory register. Programmed, a language that closely resembles a relay-based cable scheme, is normally generated with ladder logic and loaded into the CPU memory before it is used. Finally, the PLC writes or upgrades output devices via output interfaces on the basis of the software.
The aim of this new standard was to specify and standardize the design and functionality of a PLC and the vocabulary required to program it so that the users could use various PLC systems without particular difficulties. IEC 61131-3 was the first IEC published in December 1993.:
– FBD (Function block diagram): A diagram is a function block, which defines a process between the input and output variables. A set of elementary blocks is defined as a function. Linked blocks by link lines are the entrance and the output variables. A block output may also be related to a block input. House inputs and outputs with connecting lines or connections are wired. The connection is oriented, so that from the left to the right, this line carries associated data. The link line’s left and right ends must be of the same sort.
LD (Ladder diagram): Ladder logic is a programming language that demonstrates a structure based on the diagrams of relay logic. It is used primarily to develop software for industrial control applications for programmable logic controllers (PLCs). The name is because the programmers look like ladders with two vertical rails and horizontal lines between them in this language. Many of the first PLCs used basic ladder logic to convey all decision-making logic similar to the electronic diagrams. This notation was selected to minimize training requirements for current technicians.
ST (Structured text): The structured text is a block-structured high-level language that looks like Pascal.
IL (Instruction list): It is a language of the low level and looks like a montage. IEC61131 Basic Elements shares all languages. The variables and the function call are specified by the common elements, so that in the same program various languages can be used. The file format is now PLC-opened with XML.
SFC (Sequential function chart): SFC programming provides a graphical framework for program organization. Measures, acts and changes are the three key components of the SFC. Steps are just logical chunks, i.e. a programming logic unit which performs a specific control task. The interventions are the various aspects of the mission. Transitions are the processes used to switch between tasks. Control Logic is programmed in one other language, such as Ladder Diagram or Structured Text for each move, action and transition