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EMC instrumentation of the application of new materials, new devices

Power Filter Power filter is installed between the power line and electrical and electronic equipment used in p
Power Filter
    Power filter is installed between the power line and electrical and electronic equipment used in power transmission fiction parasitic electromagnetic interference , to improve the reliability of the equipment plays an important role . Filter characteristics need to be selected according to the interference source , the frequency range, voltage and impedance parameters and load characteristics.
 
Signal Transformer barrier
    The same pulse type ( digital or thyristor gate drive ) or analog isolation transformer and the AC isolation transformer used in principle , but is completely different transmission bands , some of the useful signal processing performance requirements of the transformer ( e.g., distortion , 3dB bandwidth loss , symmetry , impedance, pulse delay , etc. ) are very strict. Such transformers are broadband devices , the highest and lowest frequencies ratio fmax / fmin reach several times. By transmitting or receiving end side of the mold to cut off the loop , the isolation transformer does not change the differential mode signal while the common-mode noise fiction . Since the common -mode voltage is applied to the primary side of the transformer , the secondary side of the both sides , this isolation must have a high breakdown voltage : typically 1.5kV, in some situations as high as 10kV.
The main advantage of the signal transformer is its simple, durable, long-lasting and linear , and affordable . When the frequency increases, the electromagnetic compatibility instrument performance.
Applications:
1 ) Under conditions of low noise and low distortion analog transmission of small signal (≤ 10mV) , the signal line may exist several V to several kV common mode voltage transformer can be used to eliminate signal blocker ;
2 ) In the application circuit thyristor will trigger the drive circuit common mode voltage isolation ;
3 ) can be used to cut a ground loop and build a balanced or unbalanced connections connecting transmission lines .
 
Power isolation transformers, voltage regulators and uninterruptible power supply
( 1 ) Power Isolation Transformers
Common ground loop isolation transformer can cut off the main power line in the low frequency range. When the frequency increases, since the electrical isolation between the primary-side storage capacitor C1-2 in the presence of the drop. To reduce the influence of parasitic capacitance can be used off line , spiral , discrete primary and secondary windings , so that the parasitic capacitance can be reduced to the original 1/3 ~ / 10 .
 
Figure caption : Power Isolation Transformers [ Figure caption What does this mean ? ]
( 2 ) Faraday shield transformer
Between the primary and secondary coils wrapped in aluminum foil or copper foil, and make no contact with the coil to avoid a short circuit . Faraday shield or electrostatic shield ground . Application range is as follows :
1 ) used in the burglary power supply or power distribution box , as a simple 1:1 isolation transformers , ground loop isolation , 50/60Hz ;
2 ) a part of the same system to regenerate the AC to maintain a neutral , maintaining electrical isolation of the total power distribution point ;
3 ) When the system is applied in the presence of a large earth leakage current to prevent excessively frequent trigger system ground fault detector ;
4 ) can be used in combination with power line filters, power line filter attenuation characteristics only began in tens or hundreds of kHz or more.
 
Transient Suppressor
  And solid varistor varistor (transzorbs) is a graph of the VI characteristics of the nonlinear element can be used as the regulator element . After passing through the device when the voltage is clamped at a value equal to or greater than the breakdown voltage of the voltage VBR . Fast response speed of the device , but there are certain restrictions on the process energy value .
 
Lap, ground continuity and reduce RF impedance devices
① ground braid or metal band , wide and flat wire than the same volume of round wire cross section and has a smaller inductor. Select a reference , you can use:
Flat metal band ;
Flat ground terminal with a flat braid ;
Round, the jumper stranded .
 
② printed circuit board (PCB) ground pads.
In order to establish a more direct , low electromagnetic interference disrupt current sink , use the grounding pads. Usually in the middle of a resin-type washer spring , to provide a strong and reliable pressure on the Canadian side of the OV copper PCB mounted on the side of the chassis . Since the spring is made of copper-tin material , a good electrical contact performance, the magnitude of the contact resistance mΩ .
 
③ metal trough electricity and fertilizer were [ do not understand ] the metal braid.
Metal cable trays , the role of public wires and metal braid is part of the EMI grounding circulation of several interconnected transmission between devices . Think of it as a common-mode short-circuit path between the different chassis or ground , but in fact in addition to DC or AC 50/60Hz, this method can not be applied to longer distances ; may be used in computer room , workshop or other there are many non- tariff shield large venues , it is impossible or difficult to replace them with electricity or mount the shield pipe .
 
④ ground impedance decreases, padded metal chassis ground pad .
In order to reduce the transient conduction disturbance input and RF fields affect the surrounding environment of the system can be improved by setting the indoor reference ground floor or ground network. In this way , can easily be up to several hundred MHz frequency to achieve a 20dB improvement can also reduce potential bias in the different devices in the same room in between .
Another technique : In the interior , it is recommended to install the elevated metal floor (RMF), slabs of ribs use as a ground reference grid ; cushioning gasket replaced the plastic conductive damping pads, you can create a good lasting electrical connections.
 
⑤ temporary grounding plate .
The solution was initially planning to install IBM 's engineers have used that to install a copper or galvanized steel . For those who do not " actually ", the temporary connection between the floor because the special structure of the building a larger capacitance (300 ~ 1000pF), which gives the EMI filter , transient protection and isolation transformers to provide a Faraday shield absorbing means than there . The high end , the more effective than the virtual ground conductor .
 
   EMC testing in the actual application, except through the identification of qualified laboratory testing standards , there are two possible ways also been recognized by the industry : TCF (Technical Construction File) and a self-test to prove (Self Ceritification). The best way to achieve EMC equipment is all digital and analog circuits are considered high-frequency signal response of the circuit , the design method to deal with high-frequency electricity shield , PCB layout and common mode filtering ; using whole ground plane and supply side is also very important , so that the analog circuits , which would help limit the high frequency common mode loop . Most are transient high frequency interference , and produce a strong radiation energy.

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