Application and principle of signal isolator

1.Signal IsolatorThe role
(1) Interference of ground circulation
In the process of industrial production, various automatic instruments, control systems and actuators are needed to realize monitoring and control. The signal transmission between them includes small signals ranging from weak to millivolt and milliampere. There are also large signals of tens of volts, thousands of volts and hundreds of amperes. There are both low-frequency DC signals and high-frequency pulse signals. After the system is formed, mutual interference between instruments and equipment is often found, the system is unstable or even misoperated. In addition to the performance reasons of each instrument and equipment itself, such as anti-electromagnetic interference, there is also a very important reason that all kinds of instruments and equipment need to be grounded according to requirements and purposes. For example, for safety, the chassis needs to be grounded. In order to make the circuit work normally, the system needs to have a common reference point. In order to suppress interference and add a shielding cover, the shielding cover also needs to be grounded, however, due to the potential difference between the reference points between the instrument and the equipment (that is, the common location of each equipment is different), the problem of "ground circulation" and "ground circulation" is a problem that must be solved in the process of signal processing by the system.

(2) Natural disturbance
Lightning is a major natural source of interference, and the interference produced by lightning can be transmitted thousands of kilometers away. The time-domain waveform of lightning interference is a large spike pulse superimposed on a random pulse background. Cosmic noise is produced by ionizing radiation and changes constantly throughout the day. Solar noise changes dramatically with solar activity. Natural noise will mainly interfere with communication, and lightning energy sharp bee pulse can cause damage to many equipment, should be avoided or reduce the degree of damage, reduce losses.

(3) Human interference
The root cause of electromagnetic interference is the change of voltage or current in the conductor, that is, the larger dv/dt or di/dt.dv/dt or di/dt can make the conductor produce electromagnetic wave radiation. On the one hand, people can use this feature to achieve specific functions, such as wireless communication, radar or other functions. On the other hand, when electronic equipment is working, it will produce accompanying electromagnetic radiation due to dv/dt or di/dt in the conductor. Regardless of the subjective purpose, it objectively pollutes the electromagnetic environment. There are factories and enterprises in the production process will often have some large equipment (motor, inverter) frequent switch, they will also cause some capacitive, perceptual interference, will also affect the normal display or collection of instruments. Where there is a sudden change in voltage and current, there will certainly be electromagnetic interference. Digital pulse circuit is a typical source of interference, with the wide application of electronic technology, electromagnetic pollution will become more and more serious.

2. The method of solving all kinds of interference
First of all, the three elements of interference are interference source, sensitive source and coupling path. If one of these three elements is missing, electromagnetic compatibility problems will not exist. Therefore, we should start with these three elements. To find out the most convenient solution, the general interference source and sensitive source can not be solved, usually from the coupling path to find a way, is also the most commonly used method. Such as plus shielding, plus filtering and other means. And dealing with circulation is the most common and most troublesome, and now this is the topic of discussion.
(1) The first method; All field devices are not grounded, so that all process loops have only one grounding point and cannot form a loop. This method seems simple, but it is often difficult to realize in practical application, because some equipment requires grounding to ensure measurement accuracy or personal safety, and some equipment may form new grounding points due to long-term corrosion and wear or climate effects.

(2) The second method: make the potential of the two grounding points the same, but because the resistance of the grounding is affected by many factors of geological conditions and climate change, this method can not be completely achieved in practice.

(3) The third method: use signals in each process linkIsolator, Disconnect the process loop without affecting the normal transmission of the process signal, so as to completely solve the problem of the ground loop.

3. Adopt signalIsolatorthe superiority
Using signals in various process loopsIsolatorMethods can use DCS or PLC and other isolation cards or field with isolation of the transmitter (some equipment can do), can also use the signalIsolatorto achieve. Compare it with the signalIsolatorhas the following advantages:
• In most cases, signals are usedIsolatorNon-isolated cards are cheaper than using isolated cards.
• SignalIsolatorIt is more superior than the isolation card in terms of isolation capability and anti-electromagnetic interference.
• SignalIsolatorThe application is flexible, and it also has functions such as signal conversion and signal distribution and interface conversion, which is more convenient to use.
• SignalIsolatorUsually there are single channel, dual channel, channel completely independent of each other, constitute the configuration of the system, daily maintenance is more convenient.