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<html> <head> <meta content="en-us" http-equiv="Content-Language"> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> <link type="text/css" rel="stylesheet" href="../../../../../css/ccna.css"> <script src="../../../../../js/framesetHelper.js" language="JavaScript"></script><script language="JavaScript"> window.scrollTo(0,0); function newPage(pageID) { alert("COMMING SOON!!\nThis feature is currently in development."); } function launchMoreInfo(oid) { dash = oid.indexOf('-'); sub1 = oid.substring(0,dash); sub2 = oid.substring(dash+1); // this is an URL base on the // system that generated the static // download of the curriculum. httpref = "http://nomar.sdf.cisco.com/servlet/org.cli.delivery.rendering.servlet.MIServlet/Static=true,LMSID=DTUI,Engine=dynamic,Theme=cnamstheme,Style=ccna,Language=en,Version=2,RootID=knet-v214aCV47051/CHAPID=null/RLOID=null/RIOID=null/"; newref = httpref + sub1 +"/"+ sub2 +"/moreinfoframeset.html"; //alert("new newref :\n" + newref); window.open(newref,'MoreInfo','toolbar=no,status=yes,menubar=no,location=no,scrollbars=yes,height=442,width=756,left=20,top=20,resizable=yes') } function launchContentResource(contentID) { top.currentSupport = 0; 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That is, the AC power would be a pure sine wave of fixed amplitude and frequency. This is unfortunately not the case a can wreak havoc on networks. Surges, spikes, sags, and oscillations are introduced as deviations to the pure sine wave our devices depend upon.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>Unwanted voltage that is sent to electrical equipment is called a <i>power disturbance</i>. Typical power disturbances include voltage surges, sags, spikes, and oscillations. Another situation that can cause power problems is a total power loss.<img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47693/RIOID=knet-v214aRIO122520/knet/v214adataimage1/1.gif" width="12" height="12"></p><p> <b>Surge</b> <br>A surge is a voltage increase above 110% of the normal voltage carried by a power line. Typically, such incidents last only a few seconds. However, this type of power disruption is responsible for nearly all hardware damage that computer users experience. This is because most computer power supplies that run at 120 V are not built to handle 260 V for any length of time. Hubs are particularly vulnerable to electrical surges because of their sensitive low voltage data lines.<img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47693/RIOID=knet-v214aRIO122520/knet/v214adataimage2/2.gif" width="12" height="12"></p><p> <b>Sag/Brownout</b> <br>A sag is a brownout that lasts less than a second. These incidents occur when voltage on the power line falls below 80% of the normal voltage. Sometimes they are caused by overloaded circuits. Brownouts can also be caused intentionally by utility companies seeking to reduce the power drawn by users during peak demand periods. Like surges, sags and brownouts account for a large proportion of the power problems that affect networks and the computing devices that are attached to them.<img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47693/RIOID=knet-v214aRIO122520/knet/v214adataimage2/2.gif" width="12" height="12"></p><p> <b>Spike</b> <br>A spike is an impulse that produces a voltage overload on the power line. Spikes last between .5 and 100 microseconds. In simple terms, when a spike occurs it means that the power line has momentarily been struck with a powerful hit of at least 240 V.<img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47693/RIOID=knet-v214aRIO122520/knet/v214adataimage3/3.gif" width="12" height="12"></p><p> <b>Oscillations and Noise</b> <br>Oscillations are also sometimes referred to as harmonics, or noise. A common cause of oscillation is an excessively long electrical wiring run, which creates an antenna effect.<img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47693/RIOID=knet-v214aRIO122520/knet/v214adataimage4/4.gif" width="12" height="12"></p></td> </tr> </table> </td> </tr></table> <p> </p> <table width="100%" cellspacing="0" cellpadding="2" border="0" valign="bottom"> <tr> <td></td> </tr> </table> </body></html>⌨️ 快捷键说明
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