[原创]485总线的应用和维护

monsoon

<p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">一、关于<span lang="EN-US">485</span>总线的几个概念<span lang="EN-US">:<p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">1</span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">、<span lang="EN-US">485</span>总线的通讯距离可以达到<chmetcnv wst="on" unitname="米" sourcevalue="1200" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">1200</span>米</chmetcnv>。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">根据<span lang="EN-US">485</span>总线结构理论，在理想环境的前提下，<span lang="EN-US">485</span>总线传输距离可以达到<chmetcnv wst="on" unitname="米" sourcevalue="1200" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">1200</span>米</chmetcnv>。其条件是通讯线材优质达标，波特率为<span lang="EN-US">9600</span>，只负载一台<span lang="EN-US">485</span>设备，才能使得通讯距离达到<chmetcnv wst="on" unitname="米" sourcevalue="1200" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">1200</span>米</chmetcnv>，所以通常<span lang="EN-US">485</span>总线实际的稳定的通讯距离往往达不到<chmetcnv wst="on" unitname="米" sourcevalue="1200" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">1200</span>米</chmetcnv>。如果负载<span lang="EN-US">485</span>设备多，线材阻抗不合乎标准，线径过细，转换器品质不良，设备防雷保护复杂和波特率的提高等等因素都会降低通讯距离。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">2</span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">、<span lang="EN-US">485</span>总线可以带<span lang="EN-US">128</span>台设备进行通讯。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">其实并不是所有<span lang="EN-US">485</span>转换器都能够带<span lang="EN-US">128</span>台设备的，要根据<span lang="EN-US">485</span>转换器内芯片的型号和<span lang="EN-US">485</span>设备芯片的型号来判断，只能按照指标较低的芯片来确定其负载能力。一般<span lang="EN-US">485</span>芯片负载能力有三个级别――<span lang="EN-US">32</span>台、<span lang="EN-US">128</span>台和<span lang="EN-US">256</span>台。。此外理论上的标称往往实际上是达不到的，通讯距离越长、波特率越高、线径越细、线材质量越差、转换器品质越差、转换器电能供应不足<span lang="EN-US">(</span>无源转换器<span lang="EN-US">)</span>、防雷保护越强，这些都会降低真实负载数量。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">3</span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">、<span lang="EN-US">485</span>总线是一种最简单、最稳定、最成熟的工业总线结构<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">这种概念是错误的。<span lang="EN-US">485</span>总线是一种用于设备联网的、经济型的、传统的工业总线方式。。其通讯质量需要根据施工经验进行调试和测试采可以得到保证。<span lang="EN-US">485</span>总线虽然简单，但也必须严格按照安装施工规范进行布线。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">二、必须严格按照施工规范施工<span lang="EN-US"><p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">在<span lang="EN-US">485</span>总线系统施工时必须严格按照施工规范施工，特别应注意下面几点。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">1</font></span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">、<span lang="EN-US">485+</span>和<span lang="EN-US">485</span>－数据线一定要互为双绞。</font><span lang="EN-US"><br/><font face="宋体">2</font></span><font face="宋体">、布线一定要布多股屏蔽双绞线。多股是为了备用，屏蔽是为了便于出现特殊情况时调试，双绞是因为<span lang="EN-US">485</span>通讯采用差模通讯原理，双绞的抗干扰性较好。不采用双绞线是错误的。</font><span lang="EN-US"><br/><font face="宋体">3</font></span><font face="宋体">、<span lang="EN-US">485</span>总线一定要用手牵手式的总线结构，坚决避免星型连接和分叉连接。</font><span lang="EN-US"><br/><font face="宋体">4</font></span><font face="宋体">、设备供电的交流电及机箱一定要真实接地，而且接地良好。有很多地方表面上有三角插座，其实根本没有接地，接地良好可以防止设备被雷击、浪涌冲击。静电累积时可以配合设备的防雷设计较好地释放能量，保护<span lang="EN-US">485</span>总线设备和相关芯片不受伤害。</font><span lang="EN-US"><br/><font face="宋体">5</font></span><font face="宋体">、为避免强电对其干扰，<span lang="EN-US">485</span>总线应避免和强电走在一起。<span lang="EN-US"><p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">三、推荐几种调试方法<span lang="EN-US">:<p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">在调试前首先要确保设备接线正确，且施工合乎规范。可以根据遇到的问题采用下面几种调试方法。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">1</font></span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">、共地法<span lang="EN-US">: </span>用<span lang="EN-US">1</span>条线或者屏蔽线将所有<span lang="EN-US">485</span>设备的<span lang="EN-US">GND</span>地连接起来，这样可以避免所有设备之间存在影响通讯的电势差。</font><span lang="EN-US"><br/><font face="宋体">2</font></span><font face="宋体">、终端电阻法<span lang="EN-US">: </span>在最后一台<span lang="EN-US">485</span>设备的<span lang="EN-US">485+</span>和<span lang="EN-US">485-</span>上并接<span lang="EN-US">120</span>欧姆的终端电阻来改善通讯质量。</font><span lang="EN-US"><br/><font face="宋体">3</font></span><font face="宋体">、中间分段断开法<span lang="EN-US">: </span>通过从中间断开来检查是否设备负载过多、通讯距离过长、某台设备对整个通讯线路的影响等。</font><span lang="EN-US"><br/><font face="宋体">4</font></span><font face="宋体">、单独拉线法<span lang="EN-US">: </span>单独简易拉一条线到设备，这样可以用来排除是否是布线引起了通讯故障。</font><span lang="EN-US"><br/><font face="宋体">5</font></span><font face="宋体">、更换转换器法<span lang="EN-US">: </span>随身携带几个转换器，这样可以排除是否是转换器质量问题影响了通讯质量。</font><span lang="EN-US"><br/><font face="宋体">6</font></span><font face="宋体">、笔记本调试法<span lang="EN-US">: </span>先保证自己随身携带的<span lang="EN-US"><a href="http://www.newasp.cn/" target="_blank"><span lang="EN-US"><span lang="EN-US"><font color="#555555">电脑</font></span></span></a></span>笔记本是通讯正常的设备，用它来替换客户<span lang="EN-US"><a href="http://www.newasp.cn/" target="_blank"><span lang="EN-US"><span lang="EN-US"><font color="#555555">电脑</font></span></span></a></span>进行通讯，如果正常，则表明客户的<span lang="EN-US"><a href="http://www.newasp.cn/" target="_blank"><span lang="EN-US"><span lang="EN-US"><font color="#555555">电脑</font></span></span></a></span>的串口有可能被损害或者受伤。<span lang="EN-US"><p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">四、建议和忠告<span lang="EN-US"><p></p></span></font></span></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">&nbsp;&nbsp;&nbsp; </span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;">采用<span lang="EN-US">485</span>总线结构常见的几种通讯故障有下面几种。<span lang="EN-US"><p></p></span></span></font></p><p style="WORD-BREAK: break-all; LINE-HEIGHT: 13.5pt;"><span lang="EN-US" style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">1</font></span><span style="FONT-SIZE: 10.5pt; mso-bidi-font-family: Tahoma;"><font face="宋体">、通讯不上，无反应。</font><span lang="EN-US"><br/><font face="宋体">2</font></span><font face="宋体">、可以上传数据，但不可以下载数据。</font><span lang="EN-US"><br/><font face="宋体">3</font></span><font face="宋体">、通讯时系统提示受到干扰，或者不通讯时通讯指示灯也不停地闪烁。</font><span lang="EN-US"><br/><font face="宋体">4</font></span><font face="宋体">、有时能通讯上，有时通讯不上，有的指令可以通，有的指令不可以通。</font><span lang="EN-US"><br/></span><font face="宋体">为减少通信故障提出下面几条建议和忠告供参考。</font><span lang="EN-US"><br/><font face="宋体">1</font></span><font face="宋体">、建议用户使用和购买门禁厂家提供的<span lang="EN-US">485</span>转换器或者厂家指定推荐品牌的<span lang="EN-US">485</span>转换器。</font><span lang="EN-US"><br/><font face="宋体">2</font></span><font face="宋体">、门禁厂家会对与其配套的<span lang="EN-US">485</span>转换器做大量的测试工作，并且会要求<span lang="EN-US">485</span>转换器生产厂家按照其固定的性能参数进行生产和品质检测，所以它与门禁设备具备较好的兼容性。千万不要贪图便宜购买杂牌厂家的<span lang="EN-US">485</span>转换器。</font><span lang="EN-US"><br/><font face="宋体">3</font></span><font face="宋体">、严格按照<span lang="EN-US">485</span>总线的施工规范进行施工，杜绝任何侥幸心理。</font><span lang="EN-US"><br/><font face="宋体">4</font></span><font face="宋体">、对线路较长、负载较多的<span lang="EN-US">485</span>总线工程采用科学的、有预留的解决方案。</font><span lang="EN-US"><br/><font face="宋体">5</font></span><font face="宋体">、如果通讯距离过长， 如超<chmetcnv wst="on" unitname="米" sourcevalue="500" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">500</span>米</chmetcnv>，建议采用中继器或<span lang="EN-US">485HUB</span>来解决。</font><span lang="EN-US"><br/><font face="宋体">6</font></span><font face="宋体">、如果负载数过多，如一条总线上超过<span lang="EN-US">30</span>台，建议采用<span lang="EN-US">485HUB</span>来解决问题。</font><font face="宋体"><span lang="EN-US">
                                        <br/>7</span>、现场调试带齐调试设备。现场调试一定要随身携带几个可以接长距离和多负载的转换器、一台常用的<span lang="EN-US"><a href="http://www.newasp.cn/" target="_blank"><span lang="EN-US"><span lang="EN-US"><font color="#555555">电脑</font></span></span></a></span>笔记本、测试通路断路的万用表，几个<span lang="EN-US">120</span>欧姆的终端电阻。<span lang="EN-US"><p></p></span></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US"><p><font face="Times New Roman">&nbsp;</font></p></span></p>