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The most representative machine of the control class system – PLC

2021/03/08 > Back

Smart factory is a specific "mechanism" concept, the core part is presented as the "information system" appearance, please note that the "information system" here is different from the ERP type of "information system" or automation equipment "control system and machine arm", but a company-wide, equipment can communicate with each other "information system".

The premise of a smart factory is to use the network to connect the systems of the factory that originally operated separately (e.g., automation equipment systems, MES systems, power systems, etc.), in technical terms, to enable the "control class" system and the "information class" system to connect to each other, and to use the same communication language; The so-called "control class" system, as it is "the computer used to control the machine", in which the PLC is the most representative.

PLC is the "relay module" of automation system that used in automotive industry in the past, it is a small computer, internally equipped with microprocessors, this is the same as the general computer, but it uses a different language from the general computer, PLC language is used to symbolize the electrical circuit and compiled, so PLC programming must be done by electrical technicians with special knowledge.

A PLC can replace thousands of relay module, and since PLC is a system that communicates commands to automation equipment, its stability and precision are particularly important. We all understand that the most important thing about the operation and control of an automated device is its safety, so it must be able to react faster (its processing time) than the general information class system. As mentioned above, PLC belongs to the "control class" system rather than the “information class” system, you know, the kind of problem is not so big if information receiving delay when the network congestion in the information class system, but if it is in a control class system, the delay of any information instructions may cause serious problems.

Currently, many electric energy receivers are strongly non-linear. These types of receivers often add disturbances to the power supply network in the frequency band that is used for PLC communication, under certain circumstances, these may interfere with system communication, thereby leading to delays in executing a command. An additional element of such a system operating using PLC technology should be a filter that separates the undesirable signals (noise, interference, disturbances signals from PLC network) from the desired signal in the transmission medium. There are many EMI filter on the market, but only few fulfil PLC specific requirements. Usually, EMI filter for PLC are relatively large and expensive three-phase filter that are intended to be placed in an electrical switchboard next to the main electricity switch.

The basic task of EMI filter is to suppress the undesirable frequencies that may occur in the control signal. Filter systems are divided into different groups by considering the appropriate criteria. One of the most important of the divisions is the frequency band that is to be suppressed by the filter. Thus, there are different filters: low-pass, high-pass, band-pass (including selective broadband and narrowband) and band-stop — that suppress the signals in a specific frequency band. Other criteria that are considered in the classification of the filter are, for example, the shape of the frequency characteristics, the amplitude and phase, the type of elements that are used and the technology in the system execution.

By using an appropriate EMI filter in PLC system, it is possible to use less complex methods of error correction in the transmission of signals, thus enabling an increase in the transmission speed. In addition, due to the reduction in the complexity of the corrective methods, it is possible to use the computed savings in the capacities to implement other important functionalities or to improve the transmission security without affecting the transmission delay and user experience.

Data Source: MDPI