Signal isolator installation and maintenance precautions

Signal isolators must pay attention to the installation and maintenance Due to different manufacturers, the production process of the isolator, wiring definition are not all the same, but the use of the same situation, so the protection requirements and maintenance of the product is 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 does the PLC sometimes receive large field signal errors and poor stability? There are many reasons for this phenomenon. The potential difference between signal reference points of different instrumentation 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 equipments and meters to be the best. 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) are 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 working power and input/output are isolated, no matter how many isolators, only one power supply can be used. What if the 4-20mA channel is 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 in the market, the prices are uneven, so how do you choose? The isolator is located between two system channels. Therefore, the isolator must first determine the input and output functions. At the same time, the input and output modes (voltage, current, and loop-powered) of the isolator must be adapted to the front and rear channel interface modes. In addition, many important parameters such as accuracy, power consumption, noise, dielectric strength, and bus communication function are related 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.
How to solve the instability of the on-site two-wire pressure transmitter signal received by DCS? 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 the 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 should 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 in 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 various circuits in the input section can work normally. This series includes two-wire temperature-isolated transmitters for handling temperature sensors such as Pt100, Cu50, and thermocouples, as well as daily products for processing voltage and current signals.
There are several commonly used two-wire distributor? 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 input/output terminals and does not require a power supply. The output 4-20mA face interface is a resistive load. The choice of passive isolator products for the field transmitter distribution with PLC, DCS analog input mode to the field installation will bring great convenience. (China Branch Instrument)
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