Application of the hottest isolation device in ind

  • Detail

The application of isolation devices in industrial field

monitoring and control of production process requires a variety of automatic instruments, computers and corresponding actuators. The signals in the process include small signals of weak to millivolt level, large signals of tens of volts, and even signals of thousands of volts and hundreds of amperes to be processed. In terms of frequency, there are DC low-frequency range and high-frequency/pulse spikes. The mutual interference between equipment and instruments has become a problem that must be solved in system debugging. In addition to electromagnetic shielding, solving the "ground" of various equipment and instruments, that is, the potential difference of the signal reference point, will become an important topic. Because the signals of different equipment and instruments should be transmitted to each other, there is a problem of signal reference point. In other words, to make the signal complete transmission, the ideal situation is that the signals of all equipment and instruments have a common reference point, that is, there is a common "ground". Further, the potential difference between the reference points of all equipment and instrument signals is "zero". However, in the actual environment, this is almost impossible. In addition to the voltage drop caused by the wiring resistance between the "ground" of various equipment and instruments, there are many factors such as the different interference of various equipment and instruments in different environments, and the decline of contact quality caused by wind and rain on the wire contact, resulting in differences between the "ground". Take schematic diagram 1 as an example

figure I schematic diagram of PLC and external instruments

the figure indicates that there are two field devices 1 and 2 instruments that transmit signals to PLC and PLC sends signals to two field devices 3 and 4 instruments. It is assumed that all transmission signals are VDC. Ideally, the "ground" potentials of PLC and two field devices 1 and 2 instruments are completely equal, and there is no interference in the transmission process. From the perspective of PLC input, the reception is correct. However, as mentioned above, two field devices usually have a "ground" potential difference. For example, 1 # equipment "ground" and PLC "ground" have the same potential, 2 # equipment is 0.1V higher than their "ground" potential, so the signal from 1 # equipment to PLC is V, and the signal from 2 # equipment to PLC is 0.1v-10.1v, and the error occurs At the same time, the "ground" line of 1 #, 2 # equipment is converged and connected in the PLC, and 0.1V voltage is applied to the PLC ground strip, which may damage the local "ground" line of the PLC. At the same time, the wrong data is displayed. The problems caused by this often occur in the field commissioning, resulting in errors. For example, the production line monitoring system of a large building materials company uses American ab-plc to connect with a domestic manufacturer's manual operator. AB this rule is only applicable to single 1 fault PLC. Each data acquisition board is composed of eight channels, which share a 12 bit a/d, and the analog quantity is isolated from the host by 12 optocoupler isolators after conversion. There is no isolation between its eight channel inputs, so that when inputting signals, each channel is input separately to the acquisition full microcomputer operation board, which is normal. However, when two or more external signals are input at the same time, the display digital jump fault cannot be eliminated. Another example is that a certain Aerospace Department uses the K-type thermocouple as a sensor to test the temperature of each point of the engine. Similar to the above, it is normal when only one point is tested. However, when two or more temperature signals are connected to the host, the displayed temperature value is obviously wrong. These two cases are normal after using the isolator

The reason why the

isolator can play this role is that it has the characteristics of completely isolating the input/output electrically. In other words, there is no common "ground" between input/output, and the external signal, whether V or V with common mode interference voltage, is v after isolation. That is, the newly established "ground" after isolation has nothing to do with the "ground" of external equipment and instruments. It is for this reason that the isolation between the instrument signals of multiple external equipment input to the PLC host is also realized, that is, there is no "ground" relationship between them

the isolation between input signal and PLC signal is discussed above. Similarly, PLC output signal to external equipment also has a similar phenomenon. Obviously, using isolators can solve the problem

the product models of such voltage/voltage isolators and voltage/current isolation converters are ws1521 and ws1522

1. no matter whether PLC sends signals to external equipment and instruments or external equipment and instruments send signals to other equipment, there is often a situation: it is required that a signal can not only send signals to display instruments, but also to devices such as frequency converters. This may cause interference between two devices. To completely solve the interference problem, it is recommended to use an isolated signal distributor, whose two outputs are also isolated. It can realize the isolation between input signal and external equipment, and realize the isolation between receiving signal equipment at the same time. As shown in Figure 2

the figure cannot allow the existence of air holes. Typical applications of two isolated signal distributors

2. Field instruments may be poorly coordinated when supporting. The following situations may occur: the interface connection of receiving signal equipment (such as receiving MA) is in two-wire mode (that is, the receiving port is a 24V power supply in series with a 250 Ω), and one of the two lines of the interface is a 24V positive pole and the other is a 250 Ω end, which is suitable for connecting the field two-wire transmitter. However, the field equipment is a four wire transmitter, which outputs ma. Direct connection in this way will cause power conflict. The solution is to use an isolator to receive and isolate the Ma from the field, and install a standard two-wire transmitter on the output part of the isolator to deal with the interface of the receiving equipment. This product model is ws9030

the isolator must ensure that the input/output parts are isolated, and the additional working power supply 24V must ensure that it is electrically isolated from the two parts while supplying power to the input and output parts. This kind of device with all mutual isolation between input/output/external working power supply is called three isolation or full isolation device Theoretically, this power supply mode can be powered by a 24V power supply regardless of the number of isolators, without interference

3. For commonly used 4

Copyright © 2011 JIN SHI