PLC control cabinet is a complete set of control, can realize the motor, switch control of the electrical cabinet.
PLC control cabinet has overload, short-circuit, phase failure protection and other functions. Its structure is compact, stable, full-featured, can be combined according to the actual control of the size of the gauge, both can realize the single cabinet automatic control, can also be realized through the industrial Ethernet or industrial field bus network composed of multiple cabinets cluster (DSC) control system, can adapt to a variety of large and small-scale industrial automation control occasions, is widely used in electric power, metallurgy, chemical industry, papermaking, environmental protection, wastewater treatment and other industries. It is widely used in electric power, metallurgy, chemical industry, paper making, environmental protection and sewage treatment industries.
PLC control cabinet can complete equipment automation and process automation control, realize perfect network function, stable performance, scalable, strong anti-interference and other characteristics, is the core and soul of modern industry. Users can design PLC control cabinets, frequency conversion cabinets and so on according to their own needs, and can be matched with human-machine interface touch screen to achieve the purpose of easy operation.
Typical applications are constant pressure water supply, air compressors, fans and pumps, central air conditioning, port machinery, machine tools, boilers, paper machinery, food machinery and so on. The following is to share the relevant knowledge.
PLC control cabinet components
I. Air switch
A general air switch, which is the power control for the whole cabinet, is a necessary component for every cabinet.
II. PLC
This should be selected according to the needs of the project. If the project is small, you can directly use an integrated PLC; if the project is relatively large, you may need a module, card type, but also may need redundancy (that is, two sets of alternating use).
III. 24VDC power supply
A 24VDC switching power supply, most of the PLC is equipped with 24VDC power supply, according to the actual situation to determine whether the switching power supply.
IV. Relays
Generally the PLC is able to send commands directly to the control loop, but it may also be relayed by the relay first. If you PLC output port charged with 24VDC, but your control loop drawn in the diagram need to PLC for the node is 220VAC, then you must be added to the PLC output port a relay, that is, when the instruction is issued by the relay action, so that the node of the control loop to receive the relay's normally open or normally closed point. This is also a choice of whether to use a relay or not depending on the situation.
V. Wiring terminals
This is definitely an essential thing for every cabinet, and can be configured according to the number of signals. If it is just a simple PLC control cabinet, basically you need these things, if you need to have other equipment in the control cabinet, it depends on the situation to increase. Let's say you have the possibility of having to power certain field instruments or small control boxes, you may have to increase the number of blanks. Or if you want the PLC to be connected to a host computer, you may need to add switches or something. Depends on the situation.
PLC control cabinet use conditions
Power supply: DC DC 24V, two-phase AC 220v, (-10%, +15%), 50Hz
Protection level: IP41 or IP20
Environmental conditions: ambient temperature at 0℃-55℃, prevent direct sunlight; relative humidity of the air should be less than 85% (no condensation). Keep away from strong vibration sources, prevent frequent or continuous vibration with vibration frequency of 10-55HZ. Avoid corrosive and flammable gases.
Basic structure
I. Power supply
The power supply of the programmable logic controller plays a very important role in the whole system. Without a good, reliable power supply system is unable to work properly, therefore, the manufacturer of programmable logic controllers also attaches great importance to the design and manufacture of power supplies. General AC voltage fluctuations in the range of +10% (+15%), you can not take other measures and the PLC is directly connected to the AC power grid to go.
II. the central processing unit (CPU)
Central processing unit (CPU) is the control center of the programmable logic controller. It is in accordance with the programmable logic controller system program to give the function of receiving and storing from the programmer to key in the user program and data; check the power supply, memory, I / O, and the state of the alarm timer, and can diagnose grammatical errors in the user program.
When the programmable logic controller is put into operation, it firstly receives the status and data of each input device in the field in a scanning way and stores them into the I/O image area respectively, and then reads the user program one by one from the user program memory, and then sends the result of logical or arithmetic operation according to the provisions of the instruction to the I/O image area or the data register after the command is interpreted. After all the user programs are executed, the output states of the I/O image area or the data in the output registers are transferred to the corresponding output devices, and so on until the operation stops.
In order to further improve the reliability of programmable logic controllers, in recent years, large programmable logic controllers also use dual-CPU redundant system, or three-CPU voting system. In this way, even if a CPU failure, the entire system can still operate normally.
III. memory
Storage of system software memory is called the system program memory.
The memory for the application software is called the user program memory.
IV. Input and output interface circuits
1. The field input interface circuit consists of optically coupled circuits and microcomputer input interface circuits, the role of programmable logic controllers and field control of the interface interface input channel.
2. Field output interface circuit by the output data register, selective circuit and interrupt request circuit integration, the role of the programmable logic controller through the field output interface circuit to the field of the implementation of the corresponding control signal output components.
V. Function Modules
Such as counting, positioning and other functional modules.
VI. the communication module
Principle of operation: When the programmable logic controller into operation, its work process is generally divided into three stages, namely, input sampling, user program execution and output refresh three stages. The completion of the above three stages is called a scanning cycle. During the whole operation period, the CPU of the programmable logic controller repeats the above three phases at a certain scanning speed.
1. In the input sampling stage, the programmable logic controller reads in all input states and data sequentially in a scanning manner and stores them in the corresponding units in the I/O image area. After the input sampling is finished, it moves to the user program execution and output refresh phases. During these two phases, even if the input states and data change, the states and data of the corresponding cells in the I/O image area do not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scanning cycle to ensure that the input can be read in under any circumstances.
2. User Program Execution Phase In the user program execution phase, the programmable logic controller always scans the user program (ladder diagram) sequentially in a top-down order. When scanning each ladder diagram, it always scans the control line composed of each contact on the left side of the ladder diagram first, and performs logic operation on the control line composed of the contacts in the order of left first, then right first, then up first, then down first, and then refreshes the status of the corresponding bit of the logic coil in the system RAM memory area according to the result of the logic operation; or refreshes the status of the corresponding bit of the output coil in the I/O image area; or determining whether or not to execute a special function instruction specified in the ladder diagram. That is, during the execution of the user program, only the states and data of the input points in the I/O image area do not change, while the states and data of the other output points and the soft devices in the I/O image area or the system RAM memory area may change, and the ladder diagrams which are arranged on the top, the results of the execution of their programs will have an effect on the ladder diagrams which are arranged on the bottom and which are used with these coils or data; on the contrary, ladder diagrams which are arranged on the On the other hand, a ladder at the bottom of the ladder, the state or data of the logic coils that are refreshed will not be available to the program at the top of the ladder until the next scan cycle.
If an immediate I/O instruction is used during program execution, I/O points can be accessed directly. That is, if an I/O instruction is used, the value of the input process image register is not updated, the program takes the value directly from the I/O module, and the output process image register is updated immediately, which is a little different from immediate input.
3. Output Refresh Phase When the scanning user program is finished, the programmable logic controller enters the output refresh phase. During this period, the CPU refreshes all the output latch circuits according to the corresponding states and data in the I/O image area, and then drives the corresponding peripherals through the output circuits. At this point, the real output of the programmable logic controller.
VII. the characteristics of the programmable logic controller
1. Flexible system composition, easy to expand, with switching control as its specialty; can also be continuous process PID loop control; and can be set up with the upper body into a complex control system, such as DDC and DCS, etc., to realize the integrated automation of the production process.
2. Easy to use, simple programming, the use of concise ladder diagrams, logic diagrams or statement tables and other programming languages, without the need for computer knowledge, so the system development cycle is short, easy on-site debugging. In addition, the program can be modified online to change the control scheme without dismantling the hardware.
3. It can adapt to a variety of harsh operating environments, with strong anti-interference ability and reliability, much higher than various other models.