The working principle and function of the signal isolator What is the working principle and function of the signal isolator? Working principle: First, the signal of the transmitter or instrument is modulated by the semiconductor device, and then is isolated and converted by the light-sensing or magnetic-inductance device, and then the demodulation is converted back to the original signal before isolation, and the power of the isolated signal is also supplied at the same time. Isolate. Ensure absolute independence between transformed signals, power supply, and ground. Function: 1: Protect the lower level control loop. Second: Weaken the impact of environmental noise on the test circuit. Three: Suppress the interference of common ground, frequency converter, solenoid valve and unknown pulse to the equipment; meanwhile, it has the function of limiting pressure and flow for lower-level equipment. It is the transmitter, meter, frequency converter, solenoid valve PLC/DCS input and output, and communication. The loyal protection of the interface. The DIN series guide rail structure is easy to install and can effectively isolate: the potential between the input, output and power supply and ground. Can overcome the inverter noise and various high and low frequency pulsation interference. What are the main types of signal isolator? Isolator: In industrial production, to increase the load capacity of the instrument and ensure that the instruments connected to the same signal do not interfere with each other, and improve the electrical safety performance. Need to input the voltage, current or frequency, resistance and other signals to collect, amplify, calculate, and anti-jamming processing, and then output the isolated current and voltage signals, safe to send to the secondary instrument or plc \ dcs use. Distribution: Industrial site generally need to adopt two-wire transmission mode, not only to provide 24V distribution power supply for a meter such as a transmitter, but also to collect, amplify, calculate, and perform anti-jamming processing on the input current signal. , and then output isolated current and voltage signals for the use of secondary instrumentation or other instruments. Safety barriers: Some special industrial sites (such as gas companies and chemical plants) need not only two-wire transmission, both to provide power distribution and signal isolation functions, but also need to have the performance of safety spark explosion, reliable containment of power supply, To prevent ignition between the power supply, signal and ground, the current limiting and voltage limiting signals and the power supply circuit limit the energy entering the hazardous location within the safety quota. Signal isolators installation and maintenance should pay attention to what matters? Due to different manufacturers, the production process and wiring definition of the isolator are not all the same, but the use situation is basically the same, so the protection requirements and maintenance of the product are basically the same. 1. Read the instructions carefully before use. 2. When used as signal isolation, the input should be cascaded into the loop circuit and the output connected to the sampling loop. 3. When used as an isolated power distribution, the input should be serially connected to the power circuit and the output terminated to the transmitter. 4. If it is not working properly, check whether the wiring is correct and pay attention to the presence or absence of polarity and polarity. Why is the signal received by the PLC sometimes inaccurate and with poor stability? There are many reasons for this phenomenon. The potential difference between signal reference points of different instruments is an important factor. Because of this "potential difference" caused interference current between the instrument signal, resulting in PLC error and poor stability. Therefore, there is a common reference point for the signals of different equipment and instruments. The isolator completely isolates the inputs/outputs electrically and forms a common reference point in the PLC analog interface board. This solves the problem of achieving an ideal condition. What is the principle of designing isolated terminals? Need to allocate power for each isolator? Design follows two principles. First: Electrical isolation between external devices and central processing systems (such as PLCs, DCS). Second: External device signals (whether external devices that send signals to the central processing System or external devices that receive signals) must be electrically isolated from each other. For example, to send a signal from the PLC output to two external devices requires the input/output to be isolated and the two outputs are also isolated. If the isolated terminal's external operating power and input/output are isolated, no matter how many isolators, only one power supply can be used. Is the 4-20mA channel isolated and there is no room for power in the cabinet? Introduce a passive signal isolator, which can achieve 4-20mA signal isolation and no external power supply. MHM-05A and MHM-05C are such products. Now that there are so many brands of isolators on the market, prices vary. How can we choose? The isolator is located between two system channels, so the first choice of isolator must be to determine the input and output functions, and to make the isolator input and output modes (voltage type, current type, loop-powered type, etc.) adapt to the front and rear channel interface modes. In addition, there are many important parameters such as accuracy, power consumption, noise, dielectric strength, and bus communication function that relate to product performance, such as noise and accuracy, power consumption and reliability, which require careful selection by users. In short, the main principles for selecting isolators are their suitability, reliability, and cost-effectiveness. The on-site two-wire pressure transmitter signal received by DCS is not stable. How to solve it? The two-wire transmitter is used frequently in the industrial automation field and is the same as other industrial field devices. The two-wire transmitter also suffers from interference and interference. According to DCS analog board interface mode (current or loop power supply type), the isolation distributors with different functions are selected. In principle, it is required to provide the transmitter with isolated power and ensure that each transmitter has an independent power supply. The transmitter signal is isolated to the DCS. PLC analog board interface is a two-wire loop power supply, and the need for signal isolation, how to choose the product? The second-line loop power supply is a common analog interface. The product that fits this interface is called a two-wire loop isolation product. The isolating devices inside the isolation transmitter are all transformers. On the one hand, the signals are transmitted. On the other hand, the power at the power supply side is also transmitted to the input section, so that the various circuits of the input section can work normally. In this series, there are Pt100, Cu50, thermocouples, and other temperature sensors, as well as B5VS, B5RS, B5TS, and German weidmuller products from M-system, which handles voltage and current signals. There are several commonly used two-wire distributor? Please give examples. Commonly used two-wire isolation distributors have two series of varieties to choose from. The common point of the two series of products is that they can provide an independent isolated power supply to the two-wire transmitter through isolation from the external power supply; there are two differences, and a separate power supply is required. This power supply is isolated from the input/output. . The MHM-05 series does not require a separate power supply. It has only an input/output and does not require a power supply. The output 4-20mA face interface is a resistive load. The selection of passive isolator products for field transmitters with distribution of PLC, DCS analog input mode to the site installation will bring great convenience.
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