I personally think that the PLC will go through 5 stages. Read the content below, please ask yourself is which form!
I. logical phases
Called the logical phase is to implement the General logic of relay system design, since it is a relay system of electric drive knowledge is the basis for the stage. My personal summary learn relay system is the root of a word “seize”, the relay system is able to implement logical control in this word. Relay systems mainly have three things in a normally open b closed; c coil. This corresponds to the basic element in the PLC, but reading is not the same.
Then you can copy the original relay system? No way! Their mode of operation is not the same. Relay all hard elements start at the same tense competition in the system, and all the soft PLC elements through the PLC’s CPU to scanning process and finally calculates the result of tense, this is the PLC scanning cycle works. (Grab a book PLC has introduced)
Focus: the stage is electric drive, correspond to the normally open PLC ladder diagram; close; the coils.
Allows for simple system
II. Phase sequence control
Sequence control is widely used in industry, such as General automatic machine it is a sequential process. PLC design can achieve sequential control there are two types of methods: a PLC sequential control instruction such as Mitsubishi in STL; two way stop control. No matter what kinds of control methods in the design of the start we want to complete the process, it is the thread of the system has three main aspects: one “step” b “activities” three “conversions.”
Focus: 1. system sequence design process
2. grasp the “stop” control mode, convert ladder diagram flow chart
Can complete the General system design
III. Assembly phase
This stage is essentially different from the relay control system, is a relay control system cannot be achieved, but also improve the PLC control system of roots! I called the compilation stage, because it is very similar to the single-chip assembly language programming, such as transfer of single-chip instruction MOV, advanced instruction in the PLC is the same function. This stage is more difficult than larger, first to learn basic computer second to fully understand the PLC’s internal capabilities and resources; the third are familiar with all the features of advanced instruction (not rote memorization). If you do not understand the computer based learning advanced instruction and resources within the PLC can not understand, design very different from ideas and relay systems for example: I0.0 and IB0 first is “position” is the logical design of “points”, and the second is “bytes” not involved in the logic design.
Focus: 1. Computer basics
2. PLC resources
3. Instruction function
4. Adapted the design thinking
Can complete complex system designs
IV. Special stage
Special stage is a system of special functions, such as motion control, PID temperature control, Internet access and so on. Different functions of PLC can be different, some features are integrated within PLC and some external extensions, then depending on the object selected. Mastering this stage can greatly improve the PLC program, but also Automation other than the master PLC knowledge required, such as servo, inverter and so on.
Focus: 1. Understanding system needs
2. Reasonable selection of expansion units
3. Expansion unit using method
Can complete a special system design
That phase of the study completion date certain actual conditions
The five. Network stage
With the development of automation technology made slave PLC applications is also very common. The stage set is different to learn PLC communication protocols and communication instruction, such as PLC programming control inverter Siemens USS protocol exchanges information with the inverter. As well as industrial Ethernet and fieldbus PROFIBUS Xizi; AS-i; For a while.
MODBUS is more important in small networks, such as MODBUS protocol established through PLC and inverter to control the inverter.
Sometimes non-standard communication protocol in a network, which is used to free communication, quite flexible, but some computer network infrastructure.