1: First we must understand why the scene system can have the disturbance? What reason? How many kinds altogether has?

1) circulation disturbance
Realizes in the industrial production process monitors and controls needs to use each kind of automated measuring appliance, the control system and the implementing agency, between them the signalling already has weakly to a millivolt level, the milliampere level small signal; Some several dozens volts, even several kilovolts, several hundred ampere big signals; Also has the low frequency direct current signal, also has high frequency pulse signal and so on, after the component system often discovered transmits the mutual disturbance between the measuring appliance and the equipment, creates the system unstable even misoperation Has this kind of situation except each measuring appliance, outside the equipment itself performance reason like anti- electronmagetic interference influence, but also some extremely important reason is each kind of instrumentation equipment according to requests all to need to earth with the goal, for example in order to be safe, the cabinet needs to meet the earth; In order to cause the electric circuit normal work, the system must have the common reference point; In order to suppress the disturbance to add 屏蔽�? 屏蔽�?also needs to earth But because between the measuring appliance and between the equipment reference point has the potential difference (also is various equipment place is altogether different) thus forms "the circulation", "the earth ring circuit" the question. When the circulation is very big, can appear very high altogether traces the noise voltage, and arrives the holding wire through the distribution parameter coupling, or the direct company receives on the level holding wire, will have the very big string mold disturbance, even will damage the connection electric circuit and the equipment.
2) background
The thunder and lightning is one kind of main natural noise source, the disturbance which the thunder and lightning produces may transmit to several thousand kilometer outside place. The thunder and lightning disturbance time domain profile is the superimposition in as soon as flees in a stochastic pulse background big peak pulse. The cosmic noise is the ionisation radiation produces, unceasingly changes in one day. Solar noise along with solar activity change of situation fierce. The nature noise mainly can create the disturbance to the correspondence but the thunder and lightning energy peak pulse to be allowed to create the damage to very many equipment, should perform to avoid or to reduce the damage degree, reduces the loss.
3) jamming
The electronmagetic interference produces the basic reason is in the conductor 有电�?or the electric current change, namely bigger dv/dtdi/dt.dv/dt or di/dt can cause the conductor to produce the electromagnetic wave radiation. On the one hand, the people may use this characteristic realization specific function, for example, wireless correspondence, radar or other functions, on the other hand, electronic installation when work, because in conductor dv/dt or di/dt can produce follows the electromagnetic radiation. Regardless of on subjective stemming from any goal, on was objective has caused the pollution to the electromagnetic environment. Also has the factory enterprise to be able frequently to have some large-scale equipment in the production process (electrical machinery, frequency changer and so on) the frequent switch, they also can create some Rong Xing, the perceptual disturbance, also will affect the instrument measuring appliance normal demonstration or gathering. Every is a situation which 有电�?the electric current changes suddenly, definitely can have the electronmagetic interference existence. The digital arteries electric circuit is one kind of typical noise source. Along with the electronic technology widespread application, the electromagnetism pollution situation can be more and more serious.
2: How solves in the system three kind of disturbances?
First disturbs three essential factors are the noise source, the sensitive source and the coupling way, these three essential factors lack, the electromagnetic compatibility question all cannot save. Therefore must obtain from these three essential factors. Discovers most convenient solution, the general noise source and the sensitive source are does not have the means solution, usually is tries to find solution from the coupling way, also is the most commonly used means. If adds method and so on shield, Canadian filter. But common processes the circulation to be also most troublesome, now take this as discussion topic.
1) first method:
All scenes equipment does not earth, enable all processes ring circuit only to have 接地�? cannot the looping-in, this method look resembles simply. But in the practical application very is often difficult to realize, because certain equipment requests must earth can guarantee the measuring accuracy or the personal safety, after certain equipment are possible because encounters the corrosion and the attrition or the weather effect for a long time forms newly 接地�?
2) second method:
Causes two 接地�?electric potentials same, but because earths the resistance the geological condition and the climatic change and so on the multitudinous factor influence, this method in is actually actual also is unable versatilely to achieve.
3) third method:
Uses the signal disconnector in each process link, the separation process ring circuit, simultaneously does not affect the process signal the normal transmission, thus thorough settlement ring circuit question.
3: Why uses the signal disconnector to have the very good superiority?
Uses the signal isolation means in each process ring circuit to be allowed to use isolation card and so on the DCS or PLC or the scene belt isolation changes delivering (a minute equipment to be allowed to achieve), also may use the signal disconnector to realize. Compares below, has the merit with the signal disconnector:
• The major part situation, uses the signal disconnector + non- isolation card compared to use the isolation card small advantage
• The signal disconnector the isolation card in aspect performance and so on isolation ability, anti- electronmagetic interference is more superior than
• Signal disconnector application nimble, moreover it also has function and so on signal transformation and signal assignment and connection transformation, uses is more convenient
• The signal disconnector usually has between the single channel, the double channel, the channel mutually completely independent, the component system disposition, the routine maintenance are more convenient.
4: Now the market has that many brand the disconnector, the price is irregular, how should choose?
The disconnector is located between two systems channels, therefore the choice disconnector first must before determine the input output function, simultaneously must cause the disconnector input output pattern (voltage, electric current, ring circuit power supply and so on) to adapt rear end the channel connection pattern. In addition still had the precision □p power loss □p noise □p insulation strength □p main line communication function and so on many important parameters to involve the product performance, for example: Noise and precision related, power loss quantity of heat and reliability related, these need users cautious elect. In brief, is suitable, reliably, the product price compared to is chooses the disconnector the to be main principle.

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