PLC knowledge to get started with PLC - is what you read - programmable logic

PLC is short for 'programmable controller'. Programmable controller (original Progammadble Controllre) Shorthand for the PC, but in order to avoid and personal computer ( 个人电脑) Confused the abbreviations of the PC, so called programmable controller PLC ( Progammadble Logic Comtroller） 。 It can be seen that the PLC is a member of the family computer, is a mainly used in industrial automatic control in the field of microcomputer.

IEC ( The international electrotechnical commission) In 1987, under the programmable controller is defined as: programmable controller is a kind of digital computing operations electronic system, specially designed for application in industrial environment; It USES a programmable memory for its internal storage procedures, to perform the logic operation, sequence control, timing, counting and arithmetic operations such as user-oriented instructions; And through the digital or analog input/output control various types of machinery or production process.

PLC has a very wide range of application scope, application at home and abroad, a large number of steel, petrochemical, machinery manufacturing, automobile assembly, such as the electric power system industry automation control field.

global PLC manufacturers have hundreds, more famous is Germany's Siemens ( Siemens） Company, Rockwell automation companies in the United States, France schneider, Schneider） And omron company, Japan's mitsubishi company. Produce a large number of various types of PLC products, in our country to use more with Japan's mitsubishi FX series, Germany's Siemens S7 - 200 CPU22X series, there are a few schneider products. This lecture is based on Siemens S7 - 200 CPU224 as an example to introduce relevant knowledge.

PLC controller mainly include the basic component of the CPU ( CPU) , storage, RAM、ROM） , input and output unit ( I/O) , power supply and programmer and so on several parts.

equivalent circuit of PLC control system can be divided into three parts, namely the input, output, and the internal control part. Input part is to collect the input signal, the output part is the execution part of the system. The two parts the same as the traditional relay control circuit, the internal control are realized by the method of programming logic control circuits, with the function of software programming instead of traditional relay circuit.

PLC by external input part of the input circuit, PLC input terminal and input 'relay'. Here the so-called 'input relay' is inside the machine, visible just outside input terminals. Also can understand it, each input terminal is equivalent to a 'relay', represented by the symbol 'I', because there are many, the input terminals with digital symbols for the difference, from '0. 0 'began to count, such as the first input terminals ( And the first relay 'input') With the 'I0. 0 '. In the future and so on.

the relay coil by external input element ( Such as control button, switch, etc. ) Can't control, program control input of the relay coil. By the coil to control the action of the contact, the contact are applied in the program, according to the procedures for the change of the state to control the output. Input relay contact only two forms is a normally open contact, another is the normally closed contact, quantity are many, said casually use when programming teaching material.

output section is isolated from inside the PLC and the internal control circuit of relay output and output terminals, external load circuit. As well as input, each output terminal is then a 'output relay', its symbol by 'Q', digit symbol is also from '0. 0 'began to count, the first' output relay 'with' Q0. 0 '.

with the input of the internal procedure to control the 'output relay coil, the contact to control the external load circuit. Similarly, the 'output relay' also has two kinds of contact that is often opened normally closed contact, number is also many, to use in the program.

middle internal control circuit is formed by the user program, use the so-called 'soft relay' to instead of the actual relay control logic. Its role is in accordance with regulations of the user program logic relationship, state of the input signal and output signal detection, judgment, computing and processing, and then draw the corresponding output, to achieve the control objectives according to user's requirements.

general PLC user program is compiled with ladder diagram the graphic language. Ladder diagram looks like a traditional relay control circuit diagram, possesses the advantages of intuitive and easy to understand, it is easy to be familiar with electrical staff to grasp the traditional relay control. It is particularly suited to logical volume control switch. So we called the trapezoidal diagram of PLC controller circuit diagram and PLC program.

It is beyond doubt that benefits programmable control systems. Market sentiments are strong, especially in the light of growing plc controller price observed globally.
Shenzhen Coolmay Technology Co., Ltd. has a wide variation of including programmable control systems, plc controller price and programmable control systems, etc.
For Shenzhen Coolmay Technology Co., Ltd. as a whole to adopt an attitude of acceptance toward change and technological innovation, we first have to truly embrace it and practice what they preach. Technological development needs to be more than just another investment, but a complete integration.