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<body lang=ZH-CN link=blue vlink=blue style='tab-interval:21.0pt;text-justify-trim:
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<div class=Section1 style='layout-grid:15.6pt'>

<p><b>基本概念<span lang=EN-US><o:p></o:p></span></b></p>

<p><b>问：最近在看资料时，常遇到“电磁骚扰”和“电磁干扰”两个术语，它们有什么不同？<span lang=EN-US><o:p></o:p></span></b></p>

<p><b>答：</b>根据中华人民共和国国家标准<span lang=EN-US>GB/T4365-1995，“电磁兼容术语”，电磁骚扰和电磁干扰的定义分别如下：<o:p></o:p></span></p>

<p>　　电磁骚扰：任何可能引起装置、设备或系统性能降低或对有生命或无生命物质产生损害作用的电磁现象。电磁骚扰可能是电磁噪声、无用信号或传播媒介自身的变化。<span
lang=EN-US><o:p></o:p></span></p>

<p style='margin-left:36.0pt'>电磁干扰：电磁骚扰引起的设备、转输通道或系统性能的下降。<span lang=EN-US><o:p></o:p></span></p>

<p>　　从上面定义可知，电磁骚扰仅仅是电磁现象，即客观存在的一种物理现象，它可能引起降级或损害，但不一定已经形成后果。而电磁干扰则是电磁骚扰引起的后果。<span
lang=EN-US><o:p></o:p></span></p>

<p><b>问：电磁骚扰什么场合最多，它们是怎样产生的？<span lang=EN-US><o:p></o:p></span></b></p>

<p><b>答：</b>电磁骚扰最多的场合如下：高速数字信号线路、开关电路、脉冲发生电路和大功率控制电路等在极短的时间内电压电流急速变化的场合，所含有电感和电容的电路通断的场合。<span
lang=EN-US><o:p></o:p></span></p>

<p>　　另外，磁场、电场、电荷等电量急速变化时，同样产生电磁骚扰。<span lang=EN-US><o:p></o:p></span></p>

<p>　　开关动作的电路中，电压<span lang=EN-US>/电流的增大或衰减时间t越短，则噪声的带宽越宽；急速变化的电压V及电流I的幅值越大，则噪声的幅度越大。<o:p></o:p></span></p>

<p>　　特别是在电感性负载的电路中，电路从通转换成断的瞬间，容易产生如图<span lang=EN-US>1所示的断续的电磁干扰。图中的噪声波形由小逐渐变大，这对应了开关触点之间的距离由小到大的过程。<o:p></o:p></span></p>

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<p align=center style='text-align:center'>图<span lang=EN-US>1从通变为断时的噪声<o:p></o:p></span></p>

<p>　　在图<span lang=EN-US>2所示的电路中，直流电压V<sub>D</sub>在L和R串联的负载上产生电流I时，开关S从通转换成断的瞬间，在L两端产生比V<sub>D</sub>大数十倍、有时上百倍的极性相反的尖峰电压（称为电感反冲电压）。<o:p></o:p></span></p>

<p align=center style='text-align:center'><span lang=EN-US><!--[if gte vml 1]><v:shape
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</v:shape><![endif]--><![if !vml]><img width=400 height=395
src="./基本概念.files/image004.jpg" alt="t5-2.jpg (17427 字节)" border=1
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<p align=center style='text-align:center'>图<span lang=EN-US>2 电感电路断开的情况<o:p></o:p></span></p>

<p>　　当<span lang=EN-US>L两端有寄生电容C<sub>0</sub>时，会有以下现象：<o:p></o:p></span></p>

<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:36.0pt;text-indent:-18.0pt;mso-list:l16 level1 lfo20;tab-stops:
list 36.0pt'><![if !supportLists]><span lang=EN-US style='font-size:15.0pt'>A.<span
style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp; </span></span><![endif]><span
style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>当</span><span lang=EN-US
style='font-size:15.0pt'>C<sub>0</sub>=100pF</span><span style='font-size:15.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>时，产生约</span><span lang=EN-US style='font-size:15.0pt'> -
848V</span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>，</span><span
lang=EN-US style='font-size:15.0pt'>225kH<sub>Z</sub></span><span
style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>的振荡；</span><span style='font-size:
15.0pt'> <span lang=EN-US><o:p></o:p></span></span></p>

<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:36.0pt;text-indent:-18.0pt;mso-list:l16 level1 lfo20;tab-stops:
list 36.0pt'><![if !supportLists]><span lang=EN-US style='font-size:15.0pt'>B.<span
123

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