EMI的定義、影響因素和相關(guān)介紹

1、EMI的定義、影響因素和相關(guān)介紹電磁干擾現(xiàn)象開關(guān)電源數(shù)字脈沖電路數(shù)字視頻設(shè)備220VAC為什么要“調(diào)”電路信號畸變不能達到預(yù)期的功能信號本身失真 反射 損耗串?dāng)_地線、電源噪聲外界干擾（輻射、傳導(dǎo)）電磁兼容設(shè)計信號完整性何為EMIEMI:Electromagnetic Interference Electromagnetic energy emanating from one device which causes another device to have degraded performance 電磁 干擾引起EMI的三大要素1.干擾源 常見干擾源雷電NEMP脈沖電路ESD無線通信感性負(fù)載

2、通斷直流電機、變頻調(diào)速器電磁兼容標(biāo)準(zhǔn)分析環(huán)境中的各種電磁干擾分析設(shè)備受電磁干擾的機理編成電磁兼容標(biāo)準(zhǔn)保證各類電子設(shè)備的正常工作及良好的電磁環(huán)境國家或組織 制訂單位 標(biāo) 準(zhǔn) 編 號IECCISPR CISPR Pub. IECTC77 IEC 歐共體CENELEC EN 美國FCC，DODFCC Part , MIL-STD. 日本VCCI VCCI中國質(zhì)量技術(shù)監(jiān)督局, 國防部門GB - GJB - 標(biāo)準(zhǔn)編號的識別國際上常用EMI法規(guī)ITE產(chǎn)品定義: 1 能對資料和電信消息進行錄入,存儲,顯示,檢索,傳輸,交換或控制; 該設(shè)備可以配置一個和多個通常用于資訊傳輸?shù)慕K端. 2 額定電壓不超過600V

3、. Class B 滿足B級ITE騷擾限值的設(shè)備,主要在生活環(huán)境中使用,包括: -不在固定場所使用的設(shè)備,例如靠內(nèi)置電池供電的便攜式設(shè)備 -靠電信網(wǎng)絡(luò)供電的電信終端設(shè)備 -個人計算機及相關(guān)輔助設(shè)備 Class A 滿足A級限值但不滿足B級限值的設(shè)備,不限制其銷售,但須在 其相關(guān)使用說明中包含以下內(nèi)容的聲明: 聲明 此為A級產(chǎn)品,在生活環(huán)境中,該產(chǎn)品可能會造成無線電干擾.在這種情況下,可能需要用戶對其干擾采取切實可行的措施.ITE Production Classification Information Technology EquipmentEMI 法規(guī)的頻率范圍EMI 測量項目輻射測量(R

4、adiated Emission)傳導(dǎo)測量(Conducted Emission)諧波測量(Harmonics)電壓閃爍測量(Flicker)Radiated Emission輻射測量我們?yōu)槭裁匆M行輻射測試電磁環(huán)境日益惡劣，各個國家都相應(yīng)的制訂了關(guān)于電子類產(chǎn)品的EMC法規(guī)。要取得相應(yīng)的法規(guī)認(rèn)證后產(chǎn)品才能在此國銷售，所以。我們進行EMI測試的目的就是看產(chǎn)品是不是符合法規(guī)的要求。例如中國的CCC強制認(rèn)證。Radiated Emission當(dāng)頻率高于30MHz時，輻射變成主要的傳播方式，由兩種形式之輻射發(fā)射器：意圖與非意圖。意圖發(fā)射器，例如廣播以及雷達，會產(chǎn)生伴隨其發(fā)射信號的干擾輻射。非意圖發(fā)射器

5、，例如PC，干擾主要是伴隨其主要功能而產(chǎn)生。EMI Test Process-Radiated Emission-HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHRF Absorbing MaterialRF AmplifierReport GenerationGround Reflection Planeto eliminate reflection半無反射室實景高度掃描天線桿天線金屬地板轉(zhuǎn)臺上的受試件開闊場實景馬達驅(qū)動高度掃描天線桿天 線EUT防雨棚轉(zhuǎn) 臺 和 桌 子金屬網(wǎng)地面橢 圓 區(qū) 內(nèi) 沒 有 其 它 物 體1 電波暗室Chamber 7*4*3,適于產(chǎn)品開發(fā)

6、階段 Debug測試和Pretest2 吸波材料,吸收電磁波,減少反射3 方形木桌,可以360度旋轉(zhuǎn)(160*80*80)4 接收天線,2G以下頻率,在上下高度2m范圍內(nèi)分水平和垂直接收方向5 E7405A頻譜儀,測量頻率為9注：1 在過渡頻率處應(yīng)采用較低的限值。頻率范圍內(nèi)，限值隨頻率的對數(shù)呈線性減小。Limit 0.150.450.51.705530882162309601000CISPR22 B QPCISPR22 B AVCISPR22 A QPCISPR22 A AVFCC B QPFCC A QPFrequency(MHz)Standard(dB)5646 4650 30 37665

7、6 5660 40 47 79 73 57 50 69 63 40 47 4840 4654 60 69.549.5 566054ConductionRadiation43.5Power LineEnough is as good as a feastPeak Detect 適合對連續(xù)的大信號進行測試Quasi-Peak Detect 適合對Burst(脈沖)信號進行測試Average Detect 適合對噪聲環(huán)境中連續(xù)波小幅度信號進行測試三種檢波方式 檢波器將輸入信號功率轉(zhuǎn)換為輸出視頻電壓 對同一信號不同檢波測試: PeakQP AverageAll that ends well is we

8、ll 檢波器輸出端電壓始終能跟蹤中頻信號的峰值,及能跟蹤包絡(luò)中可能的最快變化; 若所測的所有信號都處在極限Limit以下,則產(chǎn)品合格無需進一步測試.Peak DetectorDont bite off more than you can chew Quasi-Peak testing is much slower than Peak testing. 準(zhǔn)峰值檢波器充電速率比放電速率快得多,它是按照信號的 重復(fù)頻率對信號進行衡量,隨著重復(fù)頻率的增加,檢波器沒有時間充分 放電,從而導(dǎo)致較高的輸出電壓. 對于連續(xù)(CW)波,其與峰值檢波效果一樣Quasi-Peak DetectorFortune f

9、avors the brave 峰值檢波信號通過其帶寬遠小于分辨帶寬的濾波器,該濾波器 對包絡(luò)檢波器輸出端上的高頻分量進行平均.Average DetectorThe first step is the hardest分貝（dB）的概念分貝的定義：分貝數(shù)=10lg(P2/P1) P2、P1是兩個功率數(shù)值，對于電流或電壓，定義如下： 電壓增益的分貝數(shù)=20lg(V2/V1) 電流增益的分貝數(shù)=20lg(I2/I1) 使用分貝的好處是，用較小的坐標(biāo)可以描述很寬的范圍。由于在EMC中，干擾的幅度范圍和頻率范圍都很寬，因此用分貝表示幅度，而用對數(shù)坐標(biāo)軸表示頻率更加方便。防止電磁輻射的措施最主要的是從設(shè)

10、計階段采用系統(tǒng)的設(shè)計方法，把系統(tǒng)的潛在的電磁兼容問題解決，這樣成功率高，節(jié)約開發(fā)時間和成本： Lay out方面考慮對產(chǎn)品設(shè)計階段不考慮，采用對樣品的測試修改法，但這樣可能增加成本，使產(chǎn)品的開發(fā)時間延長。Conducted Emission傳導(dǎo)測量Conducted Emission電磁能量可能以共模和差模方式傳導(dǎo)。經(jīng)由電源線，信號線，接地線，天線輸入端和其它的低阻抗路徑。在頻率30MHz以下傳導(dǎo)干擾可能性極高。高于此頻率，傳導(dǎo)干擾衰減很大，因此由其它方式來主導(dǎo)。Conduction Emission 電源端子傳導(dǎo)干擾主要測量被測設(shè)備沿電源線向電源網(wǎng)絡(luò)發(fā)射的騷擾電壓; 另一部分通過信號線傳導(dǎo)干

11、擾相連的其它周邊設(shè)備.系統(tǒng)工作時產(chǎn)生的一部分低頻信號會經(jīng)由cable線( power line and communication signal line)輻射干擾電源網(wǎng)絡(luò)和相關(guān)設(shè)備,影響連接到同一電源網(wǎng)絡(luò)的其他設(shè)備正常工作.radiation emissionmistake actionconduction emission30MHzPublic Power NetworkThe rain of tears is necessary to the harvest of learningRadiation Emission 對于較高頻(30MHz)電磁波,主要以空間傳輸進行輻射,從而影響處于同

12、一區(qū)域的其它設(shè)備的正常運行. Test location: Shielding Room (7*3*3) Test Equipments: EMC Analyzer(E7405A 9KHz26.5GHz) Receiver (ESCS 30 9KHz2750MHz) LISN (EMCO 4825/2 50 ohm 9KHz30MHz) Transient Limiter (Agilent11947A 9KHz200MHz) Test Standard : CISPR22 EN55022 FCC Part 15 Scope: Applies to IT equipment Cover the

13、frequency rang 9KHz40GHz Describes methods of measurement Standardize operation condition gives Interpretation of result gives limits Conduction EmissionTwo heads are better than oneLISN(Line Impedance Stabilization Network) LISN線性阻抗穩(wěn)定網(wǎng)絡(luò),提供純凈電源,提取EUT產(chǎn)生之雜訊信號; 由于電源端子傳導(dǎo)發(fā)射的強度與電網(wǎng)的阻抗有關(guān),因此為使測量具有唯一性,必須在特定的阻

14、抗條件下測量,LISN就提供了此種環(huán)境.GB9254標(biāo)準(zhǔn)使用LISN為50 ohm / 50 H.Transient Limiter 瞬態(tài)限制器,衰減尖峰信號,保護EMCLISN中產(chǎn)生大的尖峰信號.接地金屬板 m,最小尺寸為2m*2m.on second thoughts1 懸垂電纜末端與水平接地平板距離不足40cm,又不能縮短至適宜長度,超長部分折疊成30cm40cm的線束;2 電源線超長部分應(yīng)在中心折疊成線束或縮短至適宜的長度;3 EUT單獨與一LISN 相連,其他周邊設(shè)備通過多插座電源板接至另一LISN,LISN與EUT的水平距離應(yīng)為80cm ;4 帶電周邊設(shè)備之間相互距離為10cm,顯

15、示器可以直接放于控制器上面;5 EUT及外設(shè)的后緣須與測試桌后緣切齊;6 木桌后緣與垂直參考平面水平距離為40cm;LISN1LISN2傳導(dǎo)測試示意圖The grass is greener on the other side of the hillE7405AESCS 30Conduction Emission Test SetupControl computerLISN2LISN1HHHHHHHHHHHHHHHPrinterGround Reference PlaneVertical Ground Reference PlaneLine Impedance Stabilization Ne

16、tworkTransient LimiterTwo is company， but three is noneEMI測試最小的PC架構(gòu): 1 個人電腦 2 鍵盤 3 視訊顯示單元 4 對兩種不同形式之I/O界面,(如串行 并行口)各接一個外接周邊 5 EUT專屬之有特殊目的之周邊,如鼠標(biāo)榜 搖感等Harmonics Test諧波測量測試目的測量設(shè)備在工作時向電網(wǎng)注入的電源高次諧波的強度。看其是否符合法規(guī)要求。Why are current harmonics a problem? 1.Reduction of the effective power factor of a load*incre

17、ase of VA therefore higher cost for the electricity *higher cost based on higher rating of wires, connectors, filters, etc2. Distortion of the a.c. supply voltage*products are affected e.g. filter capacitors, overheating or reduced efficiency of motors3. EMC problems*increased harmonics current in t

18、he neutral and protective earthHarmonics SourceThe non linear load EUT generates a impulse current. Over the resistors R1 a voltage drop in line with the impulse current occur. The nonlinear impulse current is an emission of the EUT. Loads on V2 can be influenced.EUTV2R2R2V1R1VacNon-Liner Loadsvolta

19、geNon-sinusoidal e.g.:switch-mode power supply in computer, printer, television etc currentNon-sinusoidal e.g.:switch-mode power supply,With diode bridge etcIEC61000-3-2 Scope Product Family StandardPower range -230 Vrms single or three phase. For system voltages less than 220V (line to neutral), th

20、e limits have not yet been considered -Irms maximum 16A -50Hz/60Hz Measurements -measurement harmonics from 2nd to 40th Measurement Standard IEC61000-4-7 Definition of the measurement equipment and measurement procedure guideIEC61000-3-2 Test condition and limits for product familiesEquipment classe

21、sClass A:General purposes and balances three phase equipmentClass B:Portables toolsClass C:Lighting equipmentClass D:PC、PCs monitor and TV If the power level of a class D device drops below 75W, no harmonics current limits are applied and the result will always show pass.Test Conditions HarmonicsTes

22、t conditions specified in 61000-3-2: .TV .Audio amplifiers .Washing machines .Microwave ovens .Lamp dimmersPass or fail CriteriaThe average value for the individual harmonic current, taken over the entire test observation period shall be less than or equal to the application limits.For each harmonic

23、s order, all 1.5s smoothed harmonic current values shall be less than or equal to 150% of the application limits.Flicker and Voltage Fluctuation Test電壓閃爍測量Why are flicker a problem?Flickering lights creates stress in the workplace personal safety Voltage fluctuation can disrupt other products connec

24、ted to the same phase.測試目的測量EUT引起的電網(wǎng)電壓變化。電壓變化用兩個指標(biāo)表示：電壓波動和閃爍。電壓波動指標(biāo)反映了突然的較大的電壓變化程度，閃爍指標(biāo)反映了一段時間內(nèi)連續(xù)的電壓變化情況。Flicker SourceVoltage variations in low voltage network are generated from cyclical variation of loads connected to the low voltage network. The power consumption of such loads changes and theref

25、ore the current. The voltage drop across the power line impedance changes with the fluctuating current. Variation in voltage amplitude cause changes in the light output of any filament lamps.Load variationLampV changeImpedance dUGeneratorUgenExampleAutomatic turn On/Off controls such as thermostats, timer -kitchen appliances -space heaters -air conditioners -copiers -laser printersLighten Variation Human Influences a.c.uV