D201136 Anti-jamming technology in PLC applicationhttps://www.gsplcdcs.com/
1 D201136Introduction
____PLC has been widely used in tap water industry because of its strong function, brief program design, easy maintenance and other advantages, especially high reliability and strong ability to adapt to harsh industrial environment. However, due to the harsh environmental conditions, high humidity, and various industrial electromagnetic and radiation interference, it will affect the normal work of the system, so we must pay attention to the anti-interference design of the project.
The interference sources of PLC in water plant application mainly include the interference introduced by the power system, the interference introduced by the grounding system and the interference introduced by the input and output circuits. If the interference problem of PLC is not solved well, the system will not be able to operate reliably, which will affect the normal water supply. Therefore, it is necessary to discuss the interference problem in PLC application system. This paper mainly discusses three kinds of anti-interference technology of PLC.
2 D201136 Analysis of anti-interference technical countermeasures
____ In order to prevent interference, hardware and software anti-interference measures can be used, among which, hardware anti-interference is the most basic and important anti-interference measures, generally from the anti-and anti-two aspects to suppress and eliminate interference sources, cut off the coupling channel of interference to the system, reduce the sensitivity of the system to interference signals.
2.1 D201136 Interference introduced by the power system
____ The interference of power grid and frequency fluctuation will directly affect the reliability and stability of PLC system. How to suppress the interference of the power system is the main link to improve the anti-interference performance of PLC.
(1) D201136 Add filter, isolation, shielding, switching voltage regulation power supply system.
____ The function of setting the filter is to inhibit the transmission of interference signals from the power line to the system. When using the isolation transformer, it is necessary to pay attention to: the shielding layer should be well grounded; Secondary connection line to use double winding (reduce interference between wires), isolation transformer primary winding and secondary winding should be added shielding layer, the primary shielding layer connected to the AC network neutral line; The secondary shielding layer and the primary shielding layer are connected to the DC end.
In order to suppress the fluctuation of power grid voltage caused by the start and stop of large-capacity equipment (such as feed water pump, etc.) and maintain the voltage regulation of the supply voltage, the initial voltage regulation power supply can be used.
Complete set, perfect function, strong applicability
PLC has developed to today, and has formed a series of large, medium and small scale products. It can be used in various scale industrial control applications. In addition to logic processing functions, most modern PLCS have perfect data computing capabilities and can be used in various digital control fields. In recent years, a large number of PLC functional units have emerged, so that PLC has penetrated into various industrial controls such as position control, temperature control, CNC. With the enhancement of PLC communication capability and the development of human-machine interface technology, it is very easy to use PLC to form various control systems.
Easy to learn and easy to use, welcomed by engineering and technical personnel
As a general industrial control computer, PLC is an industrial control equipment for industrial and mining enterprises. Its interface is easy and the programming language is easy to be accepted by engineers and technicians. The graphic symbol of ladder diagram language is quite close to the expression mode and relay circuit diagram, and the function of relay circuit can be easily realized with only a small amount of PLC switching logic control instructions. It opens a convenient door for people who are not familiar with electronic circuits, do not understand computer principles and assembly language to use computers to engage in industrial control.
The system design, construction workload is small, easy to maintain, easy to transform
PLC uses storage logic instead of wiring logic, which greatly reduces the wiring outside the control equipment, greatly shortens the cycle of control system design and construction, and makes maintenance easier. More importantly, it is possible to change the production process with the same equipment through the modification procedure. This is very suitable for multi-variety, small batch production occasions.
D201136 Small size, light weight, low energy consumption
Taking the ultra-small PLC as an example, the newly produced varieties have a bottom size of less than 100mm, a weight of less than 150g, and a power consumption of only a few watts. Because of its small size, it is easy to be loaded into the mechanical interior, and it is an ideal control device for mechatronics.
After PLC is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution and output refresh three stages. Completing these three stages is called a scan cycle. During the entire operation period, the PLC’s CPU repeats the above three stages at a certain scanning speed.
(A) Input sampling phase
In the input sampling phase, the PLC successively reads all input status and data by scanning and stores them in the corresponding cell in the I/O image area. After the end of the input sampling, the user program execution and output refresh phase. In both phases, even if the input state and data change, the state and data of the corresponding unit in the I/O map area will not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scan cycle to ensure that the input can be read in any case.