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Industry Information
Isolators must have electromagnetic interference wherever there is a sudden change in voltage and current
2012-3-22 9:54:37

的作用:自然干扰雷电是一种主要的自然干扰源,雷电产生的干扰可以传输到数千公里以外的地方。 1. The role of the isolator : Natural interference lightning is a major natural interference source, and the interference caused by lightning can be transmitted to thousands of kilometers away. The time-domain waveform of lightning interference is a large spike on a background of a series of random pulses. Cosmic noise is generated by ionizing radiation and changes throughout the day. Solar noise changes dramatically with solar activity. Natural noise mainly interferes with communication, and lightning energy spike pulses can cause damage to many devices, and should be avoided or reduced to reduce damage and reduce losses. 2. Ground circulation interference The realization of monitoring and control in the industrial production process requires the use of various automated instruments, control systems and actuators. The signal transmission between them is as small as millivolts and milliamps; There are large signals of tens of volts, thousands of volts, and hundreds of amps; both low-frequency DC signals and high-frequency pulse signals, etc. After forming a system, it is often found that the transmission between meters and equipment interferes with each other, causing system instability and even Misoperation. In addition to the performance reasons of each instrument and equipment, such as resistance to electromagnetic interference, a very important reason is that various instruments and equipment need to be grounded according to requirements and purposes. For example, for safety, the cabinet needs Connect the ground; in order for the circuit to work properly, the system needs a common reference point; in order to suppress interference and add a shield, the shield also needs to be grounded, but because of the potential difference between the reference points between the instrument and the equipment (that is, the common Different locations) Therefore, the problems of "ground circulation" and "ground circulation" must be solved in the process of system signal processing. Problem. 3. The fundamental cause of electromagnetic interference caused by human interference is the change in voltage or current in the conductor, that is, a larger dv / dt or di / dt. Dv / dt or di / dt can cause the conductor to generate electromagnetic wave radiation. On the one hand, people can use this feature to achieve specific functions, such as infinite communication, radar, or other functions. On the other hand, when the electronic device is working, the dv / dt or di / dt in the conductor will generate accompanying electromagnetic radiation. No matter what the subjective purpose is, objectively it causes pollution to the electromagnetic environment. There are also some large-scale equipment (motors, frequency converters) that frequently switch on and off during the production process of factory enterprises. They will also cause some capacitive and inductive interference, which will also affect the normal display or collection of instruments. Where there is a sudden change in voltage and current, electromagnetic interference will definitely exist. Digital pulse circuits are a typical source of interference. With the widespread application of electronic technology, electromagnetic pollution will become more and more serious.

各种干扰的方法: Solutions to various interferences of the isolator :

First of all, the three elements of interference are interference source, sensitive source and coupling path. If one of these three elements is missing, the EMC problem will not exist. So start with these three elements. Find the most convenient solution. Generally, interference sources and sensitive sources cannot be solved. Usually, the solution is from the coupling path, which is also the most commonly used method. Such as adding shielding, filtering and other means. Dealing with circulation is the most common and most troublesome, and now this is the topic of discussion. (1) All field devices are not grounded, so that all process loops have only one ground point and cannot form a loop. This method seems simple, but it is often difficult to achieve in practical applications because some equipment requires grounding to ensure measurement accuracy. Or personal safety, some equipment may form new ground points due to long-term corrosion and wear or weather. The role of the isolator (2) makes the potentials of the two ground points the same, but because the resistance of the ground is affected by many factors such as geological conditions and climate change, this method cannot actually be achieved in practice. (3) Use a signal isolator in each process link to disconnect the process loop without affecting the normal transmission of the process signal, thereby completely solving the problem of the ground loop.
Due to different manufacturers, the production technology and wiring definition of the isolator are not the same, but the use occasions are basically the same, so the protection requirements and maintenance of the product are basically the same. 1. Read the instructions carefully before use. When used as signal isolation, the input terminal should be connected to the loop circuit, and the output terminal should be connected to the sampling circuit. 3. When used as isolated power distribution, the input terminal should be integrated into the power circuit, and the output terminal should be connected to the transmitter. 4. If it does not work properly, you should first check whether the wiring is correct, and pay attention to the power supply and polarity.
Designing isolated terminal designs follows two principles. First: The external equipment should be electrically isolated from the central processing system (such as PLC, DCS). Second: External equipment signals (whether external equipment sending signals to the central processing system or external equipment receiving signals) must be electrically isolated from each other. For example, to pass a signal output from the PLC to two external devices, the input / output needs to be isolated and the two outputs are also isolated. The two-wire loop power supply is a common analog interface. Products suitable for this interface are called two-wire loop isolation products. The isolation devices inside this isolation transmitter adopt the transformer method, on the one hand, it transmits signals, and on the other hand, it also transmits the power at the power supply end to the input part, so that the various circuits of the input part can work normally. In this series, there are WS2050, WS2060 two-wire temperature isolated transmitters that handle temperature sensors such as Pt100, Cu50, and thermocouples. There are also products such as WS2020 and WS2022 that process voltage and current signals. There are also many foreign products of the same type appearing on the market, such as the products of B5VS, B5RS, B5TS of M-system of Japan and weidmuller of Germany.

:常用的二线制隔离配电器有两个系列品种可以选择。 Several commonly used two-wire isolator : There are two series of common two-wire isolated distributors to choose from. The common feature of the two series products is that they can provide an independent isolated power supply for the two-wire transmitter after being isolated by an external power supply. There are two differences. Take WS1525 and WS2025 as examples. ① WS1525 requires a separate power supply, which is isolated from the input / output. The WS2025 does not require a separate power supply. It has only input / output terminals and no separate power terminals. ② The 4 ~ 20mA output from WS1525 is a resistance load facing the interface. The output of WS2025 is a two-wire power supply circuit in which 24VDC and the sampling resistor (or load resistance) are connected in series. Which type of isolator product to choose for the transmitter power distribution depends on the PLC and DCS analog input terminal mode configured on site. If the external working power of the isolation terminal is isolated from both the input / output, then only one power supply can be used to supply power regardless of the number of isolator.