浮地的定义

pwm

  <div id="content"><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">1</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">,干扰需要一定能量,当控制器彻底与大地隔离（浮地）时,工频干扰回路阻抗极大,流过控制器及其内部的干扰电流极小,不足以干扰倥制器。<span lang="EN-US"><br />2</span>,当控制器外壳与大地完好连接,由于控制器与大地等电位,工频干扰电流被控制器外壳接地点所旁路,无法进入控制器内部,从而也无法干扰。<span lang="EN-US"><br />3</span>,当控制器外壳与大地处于上述两者之间时,就会有工频干扰<span lang="EN-US"><br />4</span>,如果控制器的使用可能存在安全问题时,外壳必须很好接地<span lang="EN-US"><br />5</span>,多个设备的理想接地是尽量一点接大地,以避免设备间地线干扰<span lang="EN-US"><br />6</span>,有时具体问题需具体分析。<span lang="EN-US"><p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">如果几个设备互连,又无法良好接地,那么它们最好都浮地,其实这一点不太现实,在实际应用中,供电和驱动很可能用到工频电网,工频泄漏是必然的（假设绝缘阻抗<span lang="EN-US">100M</span>欧,<span lang="EN-US">380VAC</span>电压,就有<span lang="EN-US">5&#46;373uA</span>峰值漏电流流过控制器,在<span lang="EN-US">MOS</span>器件的控制器中,有的器件本身工作电流只有<span lang="EN-US">0&#46;1uA</span>）。<span lang="EN-US"><p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">所以,一般情况下,控制器外壳最好良好接地。<span lang="EN-US"><p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">如果你的确能做到所有设备与工频隔离（浮地）,如果,你的设备间没有较大的电流（这里可称信号地电流）或你的设备间信号地阻抗很小,那么,你的多个设备信号地可直接互连。否则,你的设备间信号传递需要加隔离（如光电,变压器,机械,等）。<span lang="EN-US"><p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">控制器内部电气或电子部分是否需要与外壳一点接地呢？<span lang="EN-US"><p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">当外壳与内部电路间完全浮地时,由于它们间仍存在电容藕合效应,<span lang="EN-US"><br /></span>外壳与内部电路间仍将存在工频漏电流。这时：<span lang="EN-US"><br />1</span>,当你的电路要求还不是很高时,可以不管<span lang="EN-US"><br />2</span>,当你的电路要求很高时,就必须将内部电路与外壳一点接地,同时,千万注意,同时,必须将外壳良好接大地。<span lang="EN-US"><br />3</span>,为防止内部电路与外壳一点连接时,内部输出万一碰外壳而造成短路（如电源设备）,内部电路与外壳间用容量足够大的电容相连,这样,对工频干扰来说,内部与外壳间是等电位的,对直流输出来说,是隔离的。<span lang="EN-US"><br />===========================<br /></span>地浮就是<span lang="EN-US">&quot;</span>对地浮置<span lang="EN-US">&quot;</span>,悬浮接地<span lang="EN-US">,</span>是为了克服共模干扰<span lang="EN-US">(CMR)</span>的措施<span lang="EN-US">&#46;<p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">好多地方要用浮地<span lang="EN-US">,</span>比如在<span lang="EN-US">DVM</span>的输入端<span lang="EN-US">(</span>包括<span lang="EN-US">A/D</span>转换部分<span lang="EN-US">)</span>就是使用浮地<span lang="EN-US">&#46;</span>就是该点电位与地相同<span lang="EN-US">,</span>为<span lang="EN-US">0</span>电位<span lang="EN-US">&#46;</span>但是该点又不是直接和地相连<span lang="EN-US">&#46;</span>是通过电路制造出的某个对地电位为零的点<span lang="EN-US">&#46;</span>这里的<span lang="EN-US">&quot;</span>地<span lang="EN-US">&quot;</span>也可以认为是公共端<span lang="EN-US">&#46;</span>这个<span lang="EN-US">&quot;</span>地<span lang="EN-US">&quot;</span>与实际的地间存在阻抗<span lang="EN-US">,</span>而且阻抗<span lang="EN-US">--&gt;</span>无穷<span lang="EN-US">,</span>为的就是克服共摸干扰<span lang="EN-US">&#46;<p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">比如一个极普通的例子：在同轴电缆屏蔽层两端不在同一点接地,则由于两接地点不在同一位置而造成他们之间有电压差存在<span lang="EN-US">,</span>就是共摸干扰电压<span lang="EN-US">&#46;</span>这相当于形成一干扰源串在信号源上<span lang="EN-US">,</span>既由共模干扰转化为实际发生作用的串模干扰<span lang="EN-US">&#46;</span>共模抑制比<span lang="EN-US">CMRR</span>就定义为<span lang="EN-US">:&nbsp;CMRR=20log&nbsp;Vcm/Vsm</span>,<span lang="EN-US">Vcm</span>和<span lang="EN-US">Vsm</span>分别为共摸干扰电压和其转化为相应的串摸干扰电压<span lang="EN-US">&#46;</span>而此串模干扰电压与电缆输出端<span lang="EN-US">(</span>即信号源对面的那一端<span lang="EN-US">)</span>屏蔽层对地电阻有关<span lang="EN-US">&#46;&nbsp;</span>如果此阻抗<span lang="EN-US">--&gt;</span>无穷<span lang="EN-US">,CMRR</span>就可达到很大<span lang="EN-US">,</span>所以我们可以在电缆外再加一接地的屏蔽层<span lang="EN-US">,</span>而电缆本身的屏蔽层接在浮地<span lang="EN-US">(0</span>电位点<span lang="EN-US">)&#46;</span>而在信号源端<span lang="EN-US">,</span>两屏蔽层是接在一起的<span lang="EN-US">&#46;</span>即在电缆输出端屏蔽层对地电阻<span lang="EN-US">=0</span>电位点与地间的电阻<span lang="EN-US">&#46;<p /></span></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 11&#46;25pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; TEXT-DECORATION: none; mso-bidi-font-family: 宋体; text-underline: none">另外<span lang="EN-US">,</span>在高保真的电子管放大器中<span lang="EN-US">,</span>多采用一点接地<span lang="EN-US">,</span>目的也是为了克服这种干扰<span lang="EN-US">,</span>其道理大同小异。</span></p></div>

tjuspring

我们给客户留了接地线，可惜客户都没有接上

yuninsky

不大明白。。。

flyingkimi

[s:9]  [s:19]  [s:24]

audirc

支持，仪器浮地与否常常会影响测量结果，这方面的知识还是需要多了解。