Analysis on the counting error of PLC high speed c

2022-08-08
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Analysis of the counting error of PLC high-speed counter and the methods to effectively overcome the counting error

when applying PLC high-speed counter, we often encounter the following series of problems. The pulse level of the counter and the input counting pulse signal does not match. For example, the data output of rotary encoder and grating ruler is TTL level, while the PLC high-speed counter requires to accept 0 - 24V transmission pulse signal in order to ensure the high anti-interference performance of industrial site. In order to improve the coding reliability, some encoders provide a+, a-, b+, b-, z+, z-symmetric inverted coding counting pulses, or provide a+, a-, b+, b-, z+, z-symmetric inverted sinusoidal vector differential and differential mode signals, But PLC high-speed counter requires to receive single-phase counting pulse. The user did not choose to use a suitable conversion interface and gave up one of the phases (the two-phase counting pulse signal provided by the encoder to improve the anti-interference ability of the system in the industrial field) for counting

for example, in the application of rotary encoder and grating ruler, it does not move at a uniform speed in one direction, and its movement speed is the uncertainty of time fast and time slow, time dynamic and time static, and time positive and time negative, or in the case of very low movement speed, for example, when the rotary encoder and grating ruler run at low speed, the counter is correct, and the counting error occurs when the speed is higher, and many pulses will be missed, However, the vulnerable part 1 of the selected PLC high-speed meter: the counting response frequency of the sensor counter is much higher than the motion frequency of the encoder. If the encoder does not have enough driving capacity. If the interface is not matched and processed well, the pulse data transmission distance is a little longer, the pulse transmission will be delayed, and the pulse waveform will change strangely in the process of pulse transmission. The more you know about the product, the more effective it is for the operation of the machine, and it is very prone to count errors

in many applications, although the counting pulse frequency is not high, it ignores that the PLC high-speed pulse counter has speed requirements for the front and rear edge ports of the counting pulse (the response speed of the rising and falling edge ports formed by the pulse is steep), especially when the encoder with a relatively high number of application lines is running at low speed, due to mechanical movement, it will inevitably produce subtle bucket movement or the front stage of the encoder is equipped with a speed change gear, It is easy to cause sawtooth on the front and back edge of the coding pulse. There is also mechanical wear caused by long-term mechanical movement, which will also cause sawtooth on the front and back edge of the coding pulse. And because the interference in the industrial site is complex, from the control site, such as the start and stop of motors, the switching of large current contactors, the phase modulation interference of thyristors, electric arc pulses, electromagnetic waves and other complex interference groups, the vertical and horizontal hydraulic loading to electromagnetic interference is endless

the problem is finally comprehensively reflected in the counting pulse, resulting in parasitic burr signal or parasitic interference pulse. If the parasitic burr pulse is not effectively suppressed and shaped. Therefore, it will inevitably lead to a series of problems, such as unstable and unreliable counting accuracy of PLC high-speed counter, cumulative error, and occasional counting error

therefore, many components are intact when doing simulation tests in the laboratory, but once they arrive at the industrial site, there are various abnormal phenomena. This is often due to the neglect of the overall concept of system design and the systematic interference caused by the mismatch between various systems. It will directly affect the PLC control accuracy, so that the function originally set to improve the control accuracy can not play the effect of improving the accuracy. That is, the theoretical design accuracy is far from the actual effect. Sometimes I mistakenly think that there is a problem with the quality of the PLC high-speed counter, the encoder is faulty, and the number of code disk lines is not enough. And there is no way to start without finding the source of the problem, and there are no effective measures to overcome or effective methods to overcome interference

therefore, in view of these common technical problems that are common in domestic electrical systems and industrial automation control systems, we have made a careful comparative analysis and studied many large-scale system integration projects imported from abroad, such as classic control systems with a high degree of automation control. It is found that there are many details that are often ignored by our designers - Intermediate interfaces, which are often considered to be "redundant" or components that can "save" expenses. It seems that those interface components can still work after they are removed. Some components can't reflect the changes and necessity at the moment. Especially under the unwise pressure that the current market competition is white and the price competition has become the first choice for bidding. It is often "streamlined" in terms of cost when designing. As a result, many domestic systems are naturally deficient and maladjusted, and they often get stuck during on-site system commissioning. Take emergency measures on site, and the measures taken at this time are often incomplete "small sore patches" that treat symptoms but not root causes. It is natural that the system is not durable. On the contrary, it will increase the intangible maintenance cost of the project in the future. It seems that the early project investment is responsible for the usability and the durability of the later system, which are not related to each other. The real reason lies in itself. Why can't we step over this threshold? It is very worthy of our reflection

after analyzing and studying those interface components that can be "simplified and redundant" and conducting field tests in the industrial field, we know that it is necessary for them to form the overall set of the system. Selecting the corresponding matching interfaces and maintaining the relative independence of each small system are the reliable guarantee to ensure the long-term stable operation of the large system. It also reserves the necessary space for the future system upgrade, especially in the numerical control project of mechanical and electrical integration, which requires high accuracy and rapid technology update

for this reason, we have introduced internationally advanced and mature interface technology, absorbing and digesting many targeted details. The semi domestic mhm-02a/b dual high-speed grating isolation coupler interface module and MHM-06 dual high-speed differential mode signal converter interface module are specially designed, and there are a variety of input and output mode combinations, which can meet the requirements of various forms of rotary encoder and grating ruler at home and abroad to match with various PLC controllers. It has been verified in many PLC CNC systems, especially in those "problem systems" and in the NC transformation projects of the old system. The control accuracy of many projects is significantly improved, and the theoretical design accuracy is completely consistent with the actual effect. It is indeed "more" rather than "more", which can really solve the problem and achieve twice the result with half the effort. So looking back, I find why there is a considerable gap between the products of many famous brands in the world and our similar products? By careful comparison, we really ignore the essence of knowing why and not why

in the development process of this intelligent interface, Shanghai Metallurgical Automation Research and Design Institute, Shanghai Heavy Mining Machinery Design Institute, Shanghai Machine Tool Research Institute, Shanghai Heavy Metal Continuous Casting Technology Engineering Co., Ltd., Shanghai Electric Co., Ltd., Shanghai Jiaotong University electromechanical control and logistics equipment research institute, Mets industrial systems (China) Co., Ltd., Shanghai Xinsong Robot Automation Co., Ltd With the strong support and assistance of Kunshan Shifeng Precision Machinery Co., Ltd., Shanghai Wesen Automation Technology Co., Ltd., Hangzhou Huaxin Technology Co., Ltd., Shanghai QiaoXin Precision Machinery Co., Ltd., Nanjing Skye automotive equipment manufacturing Co., Ltd., Turk (Tianjin) Automation System Co., Ltd., Shanghai internal combustion engine research institute, Shenzhen bolianda Technology Development Co., Ltd. and other units and engineering and technical personnel, I hereby express my heartfelt thanks

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