The role of programmable controllers is becoming more and more prominent, and programmable controllers are included in all major devices. In order to improve everyone’s understanding of programmable controllers, this article will introduce the selection skills of programmable controllers, the classification of programmable controllers and the technical performance indicators of programmable controllers.
1. Selection skills of programmable controller
1. The PLC brands are: Siemens, Mitsubishi, Schneider, Delta, ABB, AB, Panasonic, Omron, Xinjie, Yonghong, Inovance, LS and so on. Therefore, in general brand selection, you can choose well-known or small brands according to customer needs.
2. The general model selection is based on the principle of meeting the needs of system programming engineering, and there is no need to pursue too much. For projects with switching value as the main, select PLC according to the number of input and output points. For projects that are mainly based on analog quantities, select the analog quantity module of the PLC according to the number of analog quantity input and output channels.
3. For projects with high computing requirements, PID computing, network communication and other projects with high complexity in engineering, we give priority to medium and high-end PLCs with fast processing speed.
4. For high-speed counters, cam analog operations, RS232, RS485, etc., we give priority to intelligent control modules.
Second, the classification of programmable controllers
1. Integral programmable controller
The integral type is also called the unit type or the box type. The CPU module, I/O module and power supply of this programmable controller are housed in a box casing, and the structure is very compact. It is small in size and low in price, and the small programmable controller generally adopts an integral structure. The integral programmable controller provides a variety of basic units and expansion units with different I/O points for users to choose from. A flat cable is used to connect the unit and expansion unit.
2. Modular programmable controller
Modular is also called building block. Large and medium-sized programmable controllers and some small programmable controllers adopt a modular structure. The modular programmable controller uses building blocks to form a system, which is composed of frames and modules. The modules are plugged into the module sockets, which are soldered to the bus connection board in the frame.
3. Stackable programmable controller
Stacked structure is the product of the combination of monolithic and modular. The appearance of a certain series of programmable controller work units are made to have the same appearance and dimensions, and the CPU, I/O and power supply can also be made independent, instead of using the motherboard in the modular programmable controller, using cables to connect Each unit can be stacked layer by layer when installed in the control device, which is the stacked programmable controller. For example, the S7-200 PLC of Siemens is a stacked programmable controller.
Integral PLC is generally used in small scale, fixed number of input and output points, and there is little expansion in the future; modular PLC is generally used in large scale, more input and output points, and flexible ratio of input and output points; stacking PLC has the advantages of the first two.
3. Technical performance index of programmable controller
There are many types of programmable controllers, and users can choose PLCs with different technical performance indicators according to the specific requirements of the control system. The technical performance indicators of the programmable controller mainly include the following aspects.
1. Command system
Instruction system refers to the sum of all PLC instructions. The more programming instructions of the programmable controller, the stronger the software functions, but the more complicated it is to master the application. The user should select a programmable controller with appropriate command functions according to the actual control requirements.
2. Storage capacity
The memory of PLC consists of system program memory, user program memory and data memory. PLC storage capacity usually refers to the sum of user program memory and data memory capacity, which characterizes the available resources provided by the system to users and is an important technical indicator of system performance.
3. Communication function
Communication includes communication between PLCs and communication between PLCs and other devices. Communication mainly involves communication modules, communication interfaces, communication protocols and communication instructions. The networking and communication capabilities of PLC have also become one of the important indicators of the level of PLC products.
4. Number of input/output points
The number of I/O points of the programmable controller refers to the total number of external input and output terminals. It is an important parameter to describe the size of the PLC.
5. Scanning speed
The programmable controller works in a cyclic scan mode, and the time required to complete one scan is called the scan cycle. The main factors that affect the scanning speed are the length of the user program and the type of PLC product. The type of CPU in the PLC, the machine word length, etc. directly affect the PLC operation accuracy and running speed.
The above is the relevant content of “programmable controller” brought by this editor. Through this article, I hope that everyone has a certain understanding of programmable controller selection, programmable controller classification and programmable controller technical performance indicators.