Composition of the PLC
In terms of structure, PLC is divided into fixed and modular (modular) two. Fixed type PLC including the CPU board, I/O Board, display panel, a block of memory, power supply, these elements combine into a whole that is not removable. Modular PLC including CPU module, I/O modules, memory, power supply module, backplane, or rack, these modules can be configured according to certain rules.
CPU is PLC of core, up nerve center of role, each sets PLC at least has a CPU, it by PLC of system program gives of function received and storage user program and data, with scan of way collection by site entered device sent to of State or data, and deposit provides of left-device in the, while, diagnosis power and PLC internal circuit of work State and programming process in the of syntax errors,. After entering the run, article-by-article from the user program memory read instruction and analysis tasks a corresponding control signal as provided in instruction, to command the two control circuit.
CPU consists of ALU, controller, registers, and realize that their contact data, control and status bus, CPU modules also include peripheral chips, the bus interface and associated circuits. Main memory is used to store programs and data, is indispensable to the PLC unit.
From users point of view, without the detailed analysis of the internal circuits of the CPU, but work is in every section should have sufficient understanding. Control of CPU CPU work, read instructions, interpretation directives and instructions are executed by it. But work by the shock signal. Calculator for numeric or logical operations, under the command of the controller. Register to participate in operation and store the intermediate results of calculations, it is also a unitary deer in the controller e ao? lt;br> PLC CPU speed and memory capacity is an important parameter, which determines the speed of PLC, IO number and software capacity, so limit the control scale.
Electric circuits and PLC interface, through input and output part (I/O) completion. Integrated PLC I/O modules I/O circuit, the input registers to reflect State of the input signal, the output reflects the output latch state. Input module converting electrical signals into digital signals into the PLC system, the output module instead. I/O is divided into switch input (DI), digital output (DO), the analog input (AI), analogue outputs (AO) and so on.
Switch quantity refers only on and off (or 1 and 0) two signals, analog is a continuous change. Common I/O, is as follows:
Switching: according to the voltage level, 220VAC, 110VAC, 24VDC, isolation, isolated isolated relays and transistors.
Analog: according to the signal type, current-mode (4-20mA,0-20mA), voltage (0-10V,0-5V,-10-10V), precision, 12bit,14bit,16bit, and so on.
In addition to the common IO, but also have special IO modules, modules such as thermal resistance, thermocouple and pulse.
Specifications and quantity determined according to the I/O points module, I/O module can be more or less, but the basic configuration of the maximum number of CPU can manage ability is limited by the maximum number of blade or rack.
Power supply module
PLC power supply used to power the integrated circuit of the PLC module. While some also provide input circuit with 24V power supply. Type power input: AC power source (110VAC or 220VAC), DC power supply (24VAC).