EMI测试项目及相关法规介绍

1、introduction of emi,pceg電子r/d lab agency 2004年4月6日,电磁干扰现象,220vac,为什么要“调”电路,信号畸变,不能达到预期的功能,信号本身失真 反射 损耗,串扰,地线、电源 噪声,外界干扰 （辐射、传导）,电磁兼容设计,信号完整性,何为emi,emi:electromagnetic interference electromagnetic energy emanating from one device which causes another device to have degraded performance,电磁,干扰,引起emi的三大

2、要素,1.干扰源 2.耦合路径 3.敏感源,常见干扰源,雷电 nemp,脉冲电路,esd,无线通信,感性负载通断,直流电机、变频调速器,电磁兼容标准,分析环境中的各种电磁干扰,分析设备受电磁干扰的机理,编成电磁兼容标准,保证各类电子设备的正常工作及良好的电磁环境,标准编号的识别,国际上常用emi法规,ite产品定义: 1 能对资料和电信消息进行录入,存储,显示,检索,传输,交换或控制; 该设备可以配置一个和多个通常用于资讯传输的终端. 2 额定电压不超过600v. class b 满足b级ite骚扰限值的设备,主要在生活环境中使用,包括: -不在固定场所使用的设备,例如靠内置电池供电的便携式设

3、备 -靠电信网络供电的电信终端设备 -个人计算机及相关辅助设备 class a 满足a级限值但不满足b级限值的设备,不限制其销售,但须在 其相关使用说明中包含以下内容的声明:,声明 此为a级产品,在生活环境中,该产品可能会造成无线电干扰. 在这种情况下,可能需要用户对其干扰采取切实可行的措施.,ite production classification information technology equipment,emi 法规的频率范围,emi 测量项目,辐射测量(radiated emission) 传导测量(conducted emission) 谐波测量(harmonics) 电压闪

4、烁测量(flicker),radiated emission辐射测量,我们为什么要进行辐射测试,电磁环境日益恶劣，各个国家都相应的制订了关于电子类产品的emc法规。要取得相应的法规认证后产品才能在此国销售，所以。我们进行emi测试的目的就是看产品是不是符合法规的要求。例如中国的ccc强制认证。,radiated emission,当频率高于30mhz时，辐射变成主要的传播方式，由两种形式之辐射发射器：意图与非意图。意图发射器，例如广播以及雷达，会产生伴随其发射信号的干扰辐射。非意图发射器，例如pc，干扰主要是伴随其主要功能而产生。,emi test process -radiated emis

5、sion-,rf absorbing material,rf amplifier,ground reflection plane,to eliminate reflection,半无反射室实景,开阔场实景,1 电波暗室chamber 7*4*3,适于产品开发阶段 debug测试和pretest 2 吸波材料,吸收电磁波,减少反射 3 方形木桌,可以360度旋转(160*80*80) 4 接收天线,2g以下频率,在上下高度2m范围内分 水平和垂直接收方向 5 e7405a频谱仪,测量频率为9khz26.5ghz,注：1 在过渡频率处应采用较低的限值。 2 在0.15mhz0.5mhz频率范围内，

6、限值随频率的对数呈线性减小。,limit,enough is as good as a feast,peak detect 适合对连续的大信号进行测试 quasi-peak detect 适合对burst(脉冲)信号进行测试 average detect 适合对噪声环境中连续波小幅度信号进行测试,三种检波方式,检波器将输入信号功率转换为输出视频电压 对同一信号不同检波测试: peakqp average,all that ends well is well,检波器输出端电压始终能跟踪中频信号的峰值,及能跟踪包 络中可能的最快变化; 若所测的所有信号都处在极限limit以下,则产品合格无需 进一

7、步测试.,peak detector,quasi-peak testing is much slower than peak testing. 准峰值检波器充电速率比放电速率快得多,它是按照信号的 重复频率对信号进行衡量,随着重复频率的增加,检波器没有时间充分 放电,从而导致较高的输出电压. 对于连续(cw)波,其与峰值检波效果一样,quasi-peak detector,峰值检波信号通过其带宽远小于分辨带宽的滤波器,该滤波器 对包络检波器输出端上的高频分量进行平均.,average detector,分贝（db）的概念,分贝的定义：分贝数=10lg(p2/p1) p2、p1是两个功率数值，对

8、于电流或电压，定义如下： 电压增益的分贝数=20lg(v2/v1) 电流增益的分贝数=20lg(i2/i1) 使用分贝的好处是，用较小的坐标可以描述很宽的范围。由于在emc中，干扰的幅度范围和频率范围都很宽，因此用分贝表示幅度，而用对数坐标轴表示频率更加方便。,防止电磁辐射的措施,最主要的是从设计阶段采用系统的设计方法，把系统的潜在的电磁兼容问题解决，这样成功率高，节约开发时间和成本： 1.电路板的lay out方面考虑 2.机构方面的技术措施 对产品设计阶段不考虑，采用对样品的测试修改法，但这样可能增加成本，使产品的开发时间延长。,conducted emission传导测量,conduct

9、ed emission,电磁能量可能以共模和差模方式传导。经由电源线，信号线，接地线，天线输入端和其它的低阻抗路径。在频率30mhz以下传导干扰可能性极高。高于此频率，传导干扰衰减很大，因此由其它方式来主导。,the rain of tears is necessary to the harvest of learning,test location: shielding room (7*3*3) test equipments: emc analyzer(e7405a 9khz26.5ghz) receiver (escs 30 9khz2750mhz) lisn (emco 4825/2

10、50 ohm 9khz30mhz) transient limiter (agilent11947a 9khz200mhz) test standard : cispr22 en55022 fcc part 15 scope: applies to it equipment cover the frequency rang 9khz40ghz describes methods of measurement standardize operation condition gives interpretation of result gives limits,conduction emissio

11、n,two heads are better than one,lisn(line impedance stabilization network) lisn线性阻抗稳定网络,提供纯净电源,提取eut产生之杂讯信号; 由于电源端子传导发射的强度与电网的阻抗有关,因此为使测量具有唯一性,必须在特定的阻抗条件下测量,lisn就提供了此种环境.gb9254标准使用lisn为50 ohm / 50 h.,transient limiter 瞬态限制器,衰减尖峰信号,保护emc测试仪器的输入端不受大的瞬态信号的损伤.接通或切断被测设备电源都可能引起lisn中产生大的尖峰信号.,接地金属板 屏蔽室中接地金

12、属板须有垂直接地板和水平接地板,受试设备要放置在接地金属板上进行实验,该金属板比被测设备边框大0.5m,最小尺寸为2m*2m.,on second thoughts,1 悬垂电缆末端与水平接地平板距离不足40cm,又不能缩短至适宜长度,超长部分折叠成30cm40cm的线束; 2 电源线超长部分应在中心折叠成线束或缩短至适宜的长度; 3 eut单独与一lisn 相连,其他周边设备通过多插座电源板接至另一lisn,lisn与eut的水平距离应为80cm ; 4 带电周边设备之间相互距离为10cm,显示器可以直接放于控制器上面; 5 eut及外设的后缘须与测试桌后缘切齐; 6 木桌后缘与垂直参考平面

13、水平距离为40cm;,传导测试示意图,the grass is greener on the other side of the hill,e7405a,escs 30,conduction emission test setup,control computer,two is company， but three is none,emi测试最小的pc架构: 1 个人电脑 2 键盘 3 视讯显示单元 4 对两种不同形式之i/o界面,(如串行 并行口)各接一个外接周边 5 eut专属之有特殊目的之周边,如鼠标榜 摇感等,our conduction test area,conduction se

14、t up,lisn,harmonics test谐波测量,测试目的,测量设备在工作时向电网注入的电源高次谐波的强度。看其是否符合法规要求。,why are current harmonics a problem?,1.reduction of the effective power factor of a load *increase of va therefore higher cost for the electricity *higher cost based on higher rating of wires, connectors, filters, etc 2. distortio

15、n of the a.c. supply voltage *products are affected e.g. filter capacitors, overheating or reduced efficiency of motors 3. emc problems *increased harmonics current in the neutral and protective earth,harmonics source,the non linear load eut generates a impulse current. over the resistors r1 a volta

16、ge drop in line with the impulse current occur. the nonlinear impulse current is an emission of the eut. loads on v2 can be influenced.,eut,v2,r2,r2,v1,r1,vac,non-liner loads,voltage,non-sinusoidal e.g.:switch-mode power supply in computer, printer, television etc,current,non-sinusoidal e.g.:switch-

17、mode power supply, with diode bridge etc,iec61000-3-2 scope product family standard,power range -230 vrms single or three phase. for system voltages less than 220v (line to neutral), the limits have not yet been considered -irms maximum 16a -50hz/60hz measurements -measurement harmonics from 2nd to

18、40th,measurement standard,iec61000-4-7 definition of the measurement equipment and measurement procedure guide iec61000-3-2 test condition and limits for product families,equipment classes,class a:general purposes and balances three phase equipment class b:portables tools class c:lighting equipment

19、class 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 harmonics,test conditions specified in 61000-3-2: .tv .audio amplifiers .washing machines .microwave ovens .lamp dimmers

20、,pass or fail criteria,the 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 harmonics order, all 1.5s smoothed harmonic current values shall be less than or equal to 150% of the applicatio

21、n limits.,flicker and voltage fluctuation test电压闪烁测量,why are flicker a problem?,flickering lights creates stress in the workplace personal safety voltage fluctuation can disrupt other products connected to the same phase.,测试目的,测量eut引起的电网电压变化。电压变化用两个指标表示：电压波动和闪烁。电压波动指标反映了突然的较大的电压变化程度，闪烁指标反映了一段时间内连续的电

22、压变化情况。,flicker source,voltage 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 therefore the current. the voltage drop across the power line impedance changes with the fluctuating cu

23、rrent. variation in voltage amplitude cause changes in the light output of any filament lamps.,load variation,lamp,v change,impedance du,generator,ugen,example,automatic turn on/off controls such as thermostats, timer -kitchen appliances -space heaters -air conditioners -copiers -laser printers,lighten variation human influences,a.c.,u,voltage changes repetition rate,filament lamp 60w,human perception of flicker 50% of human are disturbed,standard: flicker,iec 61000-4-15d -measurement and instrumentations iec 61000-3-3 -product test for type test in norma