The basic composition of PLC system of hardware composition and working principle of the software

1. Hardware structure of the PLC programmable controller is mainly composed of the central processing unit ( CPU) , storage, RAM、ROM) , input and output unit ( I/O) , power supply and the programmer and so on. PLC hardware structure is shown in figure 1, figure 1 2 PLC controller hardware structure. The central processing unit (control CPU) That is commonly used in programmable controller CPU mainly adopts general microprocessor, microcontroller and bipolar slice decay processor three types. General microprocessor 8080, 8086, 80286, 80386, etc. ; Single chip computer 8031, 8096, etc; Slice AM2900 decline the processor, AM2903, etc. FX2 programmable controller used is a 16-bit microprocessor 8096 single chip microcomputer. 3. Programmable controller is equipped with two kinds of memory: memory system memory and user memory. System memory: storage system management program. User memory: storing user control program. 4. The input interface circuit of PLC through input unit which can realize the level of different input circuit transformation, into a PLC required standard level for PLC for processing. Received the PLC input interface input device is: all kinds of switches, buttons, sensors, etc. All kinds of PLC input circuit are mostly the same, with optical coupler isolation in PLC input circuit, and is equipped with the RC filter, to eliminate the input contact jitter and external noise. PLC input circuit usually has three types: direct current ( 12∽24) V input, communication ( 100∽120) V input and communication ( 200∽240) V input and ac/dc ( 12∽24) Figure 2 dc input module figure 3 V input ac and dc input module figure 4 ac input module 5. Output interface circuit of PLC output has three forms, namely the relay output, the output transistor, thyristor output. : as shown in figure 5 field effect transistor output way ( Dc output) Figure 6 SCR output way ( Ac output) Figure 7 relay output ( Ac/dc output) There are two kinds of output terminal connection: one is the output independently, without a common point: the output terminal to form independent circuits. One for every four ∽ eight dots form a group, share a common point: when sharing a common terminal in the output, must use the same voltage type and the same voltage grade, but different public point group can use different voltage type and grade of load, and the output is isolated between the common point. Input and output terminal handling process is as follows: 6. Power supply of the PLC power supply power supply is generally, also useful dc 24 v power supply. 7. Programmer using programmer can input the user program to the PLC memory, you can also use programmer check program, modify the program; Use programmer can also monitor the working state of PLC. General component is simple and smart programmer. 8. In software structure of the PLC programmable controller, PLC software is divided into two parts: 1. System monitoring program: used to control the operation of the programmable controller itself. Is mainly composed of management procedures, user command interpreter and standard module, system calls. 2. User program: it is by the users of the programmable controller, is used to control by the operation of the control unit.
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