不尋常的結(jié)構(gòu)給予保險(xiǎn)絲對(duì)瞬間浪涌電流的“記憶”能力。

　　在我事業(yè)中期，我成為一名器件工程師。不久之后，我到了新部門，面對(duì)一個(gè)一段時(shí)間內(nèi)都存在的問(wèn)題。crt顯示器中看似簡(jiǎn)單的保險(xiǎn)絲卻出現(xiàn)很高的故障率。我們已經(jīng)按照說(shuō)明書徹底地測(cè)試了樣品。一個(gè)測(cè)試工程師以前曾設(shè)計(jì)了測(cè)試工裝，以便對(duì)一批保險(xiǎn)絲測(cè)試所有的指標(biāo)條款。說(shuō)明書要求保險(xiǎn)絲在超過(guò)正常溫度、振動(dòng)和擺動(dòng)指標(biāo)的某個(gè)百分比后幾毫秒內(nèi)斷開。原先的工程師進(jìn)行了很多測(cè)試工作，驗(yàn)證了保險(xiǎn)絲滿足所有的規(guī)范。

　　然而，在應(yīng)用中，高失效率仍在繼續(xù)。第一步，我測(cè)量了實(shí)際應(yīng)用中的電流，確保保險(xiǎn)絲的選擇合適。我發(fā)現(xiàn)，除了小且簡(jiǎn)短的上升電流外，標(biāo)稱值在保險(xiǎn)絲的額定范圍之內(nèi)的，會(huì)快速上升到標(biāo)稱值。我懷疑是簡(jiǎn)短的上電浪涌引起了問(wèn)題。仔細(xì)檢查原先的測(cè)試結(jié)果和應(yīng)用測(cè)試后，我認(rèn)為這不能解釋高失效率的問(wèn)題。絕望中，我送一些樣品到定點(diǎn)材料實(shí)驗(yàn)室，讓那里的同事測(cè)試保險(xiǎn)絲的橫截面直徑，并鑒別所使用的合金。很幸運(yùn)地，實(shí)驗(yàn)室將工作分配給了一位有能力的材料工程師，他把保險(xiǎn)絲做了瞬間電流脈沖實(shí)驗(yàn)后，送去做了額外的分析。幾天后，我拿到了漂亮的縮影照片顯示了意想不到的結(jié)構(gòu)技術(shù)。照片顯
示保險(xiǎn)絲由三種金屬組成，而不是使用某種低熔點(diǎn)金屬的單一合金。它有一個(gè)大圓形鎢內(nèi)核。穿過(guò)鎢是一個(gè)銅薄板；另一個(gè)銀薄板又覆蓋了銅薄板。更令人驚訝的是工程師送去的經(jīng)過(guò)瞬間過(guò)電流的保險(xiǎn)絲。他發(fā)現(xiàn)通過(guò)電容充電到各種電壓，用保險(xiǎn)絲短路放電，可以形成一個(gè)可控的浪涌電流。照片顯示若干次浪涌后，銀板達(dá)到熔點(diǎn)液化。更多浪涌后，銀板完全熔化，只留下帶薄銅板的鎢核。因?yàn)殂y有很強(qiáng)的電傳導(dǎo)性，實(shí)質(zhì)上所有浪涌的電流最初都完整的通過(guò)外部銀層流動(dòng)。然后，另外的浪涌大多數(shù)通過(guò)薄銅板流動(dòng)，因?yàn)殂~具有比鎢更高的傳導(dǎo)性。那個(gè)層最終熔化了。現(xiàn)在，只剩下高阻的鎢核。隨著更多的浪涌，所有電流現(xiàn)在都不得不通過(guò)剩下的鎢核流動(dòng)。當(dāng)更多浪涌發(fā)生時(shí)，鎢逐漸加熱到足夠變薄，最后斷開。

　　我們隨后意識(shí)到這種層構(gòu)造技術(shù)使保險(xiǎn)絲具有了“記憶”瞬間過(guò)載電流浪涌累積的能力。上電的每個(gè)浪涌貢獻(xiàn)了小改變，最終導(dǎo)致保險(xiǎn)絲斷開。穩(wěn)態(tài)測(cè)試沒(méi)能顯示出這個(gè)特性。其三層構(gòu)造和金屬使用的結(jié)果，使保險(xiǎn)絲具有記憶性。解決方法是改變?yōu)閭鹘y(tǒng)的單一元素低熔點(diǎn)合金的保險(xiǎn)絲——也就是不具有記憶能力的保險(xiǎn)絲。這個(gè)實(shí)現(xiàn)是許多這種發(fā)現(xiàn)的開始——可以通過(guò)溯源到基礎(chǔ)知識(shí)來(lái)診斷大多數(shù)問(wèn)題。

　　英文原文：

　　blown fuse has a meltdown

　　tales from the cube: unusual construction gives fuse a "memory" for brief current surges.

　　by jim sylivant, engineering consultant -- edn, 1/17/2008

　　in midcareer, i became a component engineer. soon after i arrived in my new department, i faced a problem that had been ongoing for some time. it seems that a simple fuse in a crt display had been having high failure rates. my new department had thoroughly tested samples against its specifications. a previous test engineer had designed a test fixture so that he could test batches of this fuse for all spec items. the specification required the fuse to open at a certain percentage over its nominal rating within a certain number of milliseconds over a range of temperatures, as well as after shock and vibrations. the previous engineer had done a splendid job of testing to verify that the fuse met all specifications.

　however, in the application, high failure rates continued. my first step was to measure actual current in the application to ensure that we had chosen the proper fuse. i found that, besides a small, brief start-up current, the nominal value quickly settled to values well within the fuse's rating. i didn't suspect the brief start-up surge of causing a problem. after going over previous test results and in-application testing, i could find no explanation for the high failure rate. in desperation, i sent some samples to our on-site materials lab and asked the folks there to measure the cross-section diameter of the fuse element and identify the alloy used. fortunately, the lab assigned the job to a very competent materials engineer who went the extra mile by analyzing the fuse after subjecting it to brief current pulses. in a few days, i got back beautiful microphotographs showing an unexpected construction technique. the photos showed that, instead of using a single alloy of some low-melt