plc control cabinet structure introduction

Introduction plc control cabinet such a device believe that everyone does not know, except for some friends who specialize in related professions. Nowadays, industrial control technology is constantly developing, such as plc control cabinet equipment to a certain extent plays a great role. Therefore, for this kind of equipment for the general knowledge of the study, can bring a lot of help for the work of friends in the future. Below I will introduce the structure of the plc control cabinet, so that friends understand the specific composition of which some. plc control cabinet is the most core control system of industrial control equipment, it can effectively control the corresponding industrial control equipment, so that it carries out normal work. So what are the components of the PLC control cabinet? What is its structure? Let me introduce to you.

plc control cabinet composition

The general plc control cabinet is composed of five parts: switch, plc, power supply, relays and terminals. Each component has its own unique role. Here we come to the doctrine of the introduction.

First of all, for the air switch, it is a more important air switch as a control power source, which can control the power supply to the overall cabinet. It is also something very necessary for every installation that needs to have such a device.

The second is PLC, based on different projects, their needs are different, the choice is also different. We can give an example to illustrate, for the project is very small, then, in practice, you can completely use the integrated plc; project if very large, then, for the plc requirements are more stringent, may choose the module or card type. In some projects, even need to prepare redundant PLC.

Again is the power supply, for this part, is plc comes with. The switching power supply is usually 24VDC, which is still required for most plc's, but for exceptions, it is designed based on specific needs.

Next is the relay. Usually the PLC is able to send commands directly to the control loop, and it is relatively common for relays to relay these commands. An example to illustrate: If the PLC output port 24VDC voltage, but the corresponding control loop voltage required is 220VAC, this problem we only need to use the way to solve the relay. The actual operation is when the command is issued, the relay will be actuated, through the specific needs to determine whether to use the relay device.

Lastly, there is the terminal block. This device is an indispensable thing for signal transmission, but also this kind of equipment must be used. How much of it is used depends entirely on the number of signals. For simple PLC control cabinets, the use of a little is enough, but to add other things in the cabinet, then you need to increase according to the need.

PLC control cabinet working principle

When the PLC is put into operation, its work process is generally divided into three phases, namely, the input sampling, user program execution and output refresh three stages. The completion of these three stages is called a scanning cycle. During the entire operation period, the PLC's CPU repeats the above three phases at a certain scanning speed.

(I)? Input sampling phase? During the input sampling phase, the PLC reads in all input states and data 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 stages. 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 pulsed signal, the width of that pulsed signal must be greater than one scan cycle to ensure that the input can be read in under any circumstances.

(ii)? User program execution phase? During the user program execution phase, the PLC always scans the user program (ladder diagram) sequentially in top-to-bottom order. In scanning each ladder diagram, and always scan the left side of the ladder diagram by the contacts constitute the control line, and according to the first left and then right, first up and then down the order of the contacts constitute the control line for logical operations, and then according to the results of the logical operations, refresh the logic coil in the system RAM storage area in the state of the corresponding bit; or refresh the output coil in the corresponding bit of the state of the I / O image area; or Determine whether to execute the special function instructions specified in the ladder diagram.

That is, in the process of user program execution, only the state and data of the input points in the I/O image area will not change, while the state and data of the other output points and soft devices in the I/O image area or the system RAM memory area may change, and the ladder diagrams lined up on top of the results of program execution will play a role in the ladder diagrams below the rows of any use of these coils or data; on the contrary, the ladder diagrams lined up on top of the results of program execution will play a role in the ladder diagrams below. On the contrary, the status or data of the refreshed logic coils of the ladder at the bottom of the ladder will only be available to the program above it 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 somewhat different from immediate input.

(iii)? Output refresh phase? When the scanning user program is finished, the PLC enters the output refresh phase. During this period, the CPU refreshes all the output latch circuits in accordance with the corresponding states and data in the I/O image area, and then drives the corresponding peripherals through the output circuits. At this point, it is the real output of the PLC.

Above we introduced the plc control cabinet of some of the structure of the main components, these parts in its operation are assumed a very important role. I hope this article can give friends some inspiration.

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