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示波器的基本原理-顯示電路
顯示(shi)(shi)電路包括示(shi)(shi)波管及其(qi)控制電路兩個部(bu)分。示(shi)(shi)波管是一種(zhong)特殊的電子管，是示(shi)(shi)波器(qi)一個重要組成部(bu)分。示(shi)(shi)波管由電子槍、偏轉系統(tong)和熒光屏3個部(bu)分組成。
（1）電子槍
電子(zi)(zi)槍用于(yu)產生(sheng)并形成高速(su)、聚(ju)束的電子(zi)(zi)流，去轟擊熒光(guang)屏(ping)(ping)(ping)使之發光(guang)。它主要由(you)燈(deng)絲F、陰極(ji)(ji)K、控(kong)制(zhi)極(ji)(ji)G、第一陽極(ji)(ji)A1、第二(er)陽極(ji)(ji)A2組(zu)成。除燈(deng)絲外，其(qi)余電極(ji)(ji)的結構(gou)都為(wei)金屬(shu)圓筒，且(qie)它們的軸(zhou)心(xin)都保持在(zai)同一軸(zhou)線上(shang)。陰極(ji)(ji)被加(jia)熱后，可沿軸(zhou)向發射電子(zi)(zi)；控(kong)制(zhi)極(ji)(ji)相(xiang)對陰極(ji)(ji)來說是(shi)負電位(wei)，改變電位(wei)可以改變通(tong)過控(kong)制(zhi)極(ji)(ji)小(xiao)孔的電子(zi)(zi)數(shu)目(mu)，也就是(shi)控(kong)制(zhi)熒光(guang)屏(ping)(ping)(ping)上(shang)光(guang)點(dian)的亮度。為(wei)了提高屏(ping)(ping)(ping)上(shang)光(guang)點(dian)亮度，又不降低對電子(zi)(zi)束偏(pian)(pian)轉(zhuan)(zhuan)的靈敏度，現(xian)代(dai)示(shi)波管中，在(zai)偏(pian)(pian)轉(zhuan)(zhuan)系統和熒光(guang)屏(ping)(ping)(ping)之間還加(jia)上(shang)一個(ge)后加(jia)速(su)電極(ji)(ji)A3。
第(di)(di)一(yi)陽(yang)極(ji)(ji)對陰極(ji)(ji)而言加有約(yue)幾百伏的(de)(de)(de)(de)(de)(de)正電(dian)(dian)壓。在(zai)第(di)(di)二(er)陽(yang)極(ji)(ji)上(shang)(shang)加有一(yi)個比第(di)(di)一(yi)陽(yang)極(ji)(ji)更高(gao)的(de)(de)(de)(de)(de)(de)正電(dian)(dian)壓。穿(chuan)過(guo)控制極(ji)(ji)小孔的(de)(de)(de)(de)(de)(de)電(dian)(dian)子束(shu)，在(zai)第(di)(di)一(yi)陽(yang)極(ji)(ji)和(he)第(di)(di)二(er)陽(yang)*電(dian)(dian)位(wei)的(de)(de)(de)(de)(de)(de)作(zuo)用(yong)下，得到加速(su)，向(xiang)熒光(guang)屏(ping)方向(xiang)作(zuo)高(gao)速(su)運動。由(you)于(yu)電(dian)(dian)荷的(de)(de)(de)(de)(de)(de)同(tong)性相斥，電(dian)(dian)子束(shu)會(hui)(hui)逐漸散開。通(tong)過(guo)第(di)(di)一(yi)陽(yang)極(ji)(ji)、第(di)(di)二(er)陽(yang)極(ji)(ji)之(zhi)間(jian)(jian)電(dian)(dian)場(chang)的(de)(de)(de)(de)(de)(de)聚焦作(zuo)用(yong)，使(shi)(shi)電(dian)(dian)子重新聚集起(qi)來并交匯(hui)于(yu)一(yi)點(dian)。適(shi)當(dang)控制第(di)(di)一(yi)陽(yang)極(ji)(ji)和(he)第(di)(di)二(er)陽(yang)極(ji)(ji)之(zhi)間(jian)(jian)電(dian)(dian)位(wei)差的(de)(de)(de)(de)(de)(de)大(da)小，便能使(shi)(shi)焦點(dian)剛好落在(zai)熒光(guang)屏(ping)上(shang)(shang)，顯現一(yi)個光(guang)亮細小的(de)(de)(de)(de)(de)(de)圓(yuan)點(dian)。改變(bian)第(di)(di)一(yi)陽(yang)極(ji)(ji)和(he)第(di)(di)二(er)陽(yang)極(ji)(ji)之(zhi)間(jian)(jian)的(de)(de)(de)(de)(de)(de)電(dian)(dian)位(wei)差，可起(qi)調節光(guang)點(dian)聚焦的(de)(de)(de)(de)(de)(de)作(zuo)用(yong)，這就(jiu)是示(shi)波器的(de)(de)(de)(de)(de)(de)“聚焦"和(he)“輔助聚焦"調節的(de)(de)(de)(de)(de)(de)原理。第(di)(di)三陽(yang)極(ji)(ji)是示(shi)波管錐體內(nei)部涂上(shang)(shang)一(yi)層(ceng)石墨(mo)形(xing)成的(de)(de)(de)(de)(de)(de)，通(tong)常(chang)加有很高(gao)的(de)(de)(de)(de)(de)(de)電(dian)(dian)壓，它有三個作(zuo)用(yong)：①使(shi)(shi)穿(chuan)過(guo)偏(pian)轉系統(tong)以(yi)后的(de)(de)(de)(de)(de)(de)電(dian)(dian)子進一(yi)步加速(su)，使(shi)(shi)電(dian)(dian)子有足夠(gou)的(de)(de)(de)(de)(de)(de)能量去轟(hong)擊(ji)熒光(guang)屏(ping)，以(yi)獲得足夠(gou)的(de)(de)(de)(de)(de)(de)亮度；②石墨(mo)層(ceng)涂在(zai)整個錐體上(shang)(shang)，能起(qi)到屏(ping)蔽作(zuo)用(yong)；③電(dian)(dian)子束(shu)轟(hong)擊(ji)熒光(guang)屏(ping)會(hui)(hui)產生(sheng)二(er)次電(dian)(dian)子，處于(yu)高(gao)電(dian)(dian)位(wei)的(de)(de)(de)(de)(de)(de)A3可吸收這些(xie)電(dian)(dian)子。
(2)偏轉系統
示(shi)波管的(de)偏(pian)(pian)(pian)轉系(xi)統(tong)大都(dou)是(shi)靜電(dian)(dian)偏(pian)(pian)(pian)轉式，它由兩(liang)對相互(hu)垂(chui)(chui)直的(de)平(ping)行金屬板(ban)組成，分(fen)(fen)別(bie)稱為水平(ping)偏(pian)(pian)(pian)轉板(ban)和垂(chui)(chui)直偏(pian)(pian)(pian)轉板(ban)。分(fen)(fen)別(bie)控制電(dian)(dian)子束在(zai)水平(ping)方向(xiang)和垂(chui)(chui)直方向(xiang)的(de)運動。當電(dian)(dian)子在(zai)偏(pian)(pian)(pian)轉板(ban)之(zhi)(zhi)間(jian)運動時，如果偏(pian)(pian)(pian)轉板(ban)上沒有加(jia)電(dian)(dian)壓(ya)，偏(pian)(pian)(pian)轉板(ban)之(zhi)(zhi)間(jian)無(wu)電(dian)(dian)場，離開第二陽極后進(jin)入偏(pian)(pian)(pian)轉系(xi)統(tong)的(de)電(dian)(dian)子將沿(yan)軸向(xiang)運動，射向(xiang)屏幕的(de)中心(xin)。如果偏(pian)(pian)(pian)轉板(ban)上有電(dian)(dian)壓(ya)，偏(pian)(pian)(pian)轉板(ban)之(zhi)(zhi)間(jian)則有電(dian)(dian)場，進(jin)入偏(pian)(pian)(pian)轉系(xi)統(tong)的(de)電(dian)(dian)子會在(zai)偏(pian)(pian)(pian)轉電(dian)(dian)場的(de)作用下(xia)射向(xiang)熒光屏的(de)定位(wei)置。
如果兩塊偏(pian)(pian)(pian)轉(zhuan)板(ban)互相平(ping)行，并(bing)且(qie)它們的(de)電(dian)(dian)位差(cha)等于(yu)零，那(nei)么通(tong)過偏(pian)(pian)(pian)轉(zhuan)板(ban)空間的(de)，具有速度υ的(de)電(dian)(dian)子(zi)束就會沿(yan)著(zhu)原方向(xiang)(xiang)（設為軸(zhou)線方向(xiang)(xiang)）運動(dong)，并(bing)打在熒光屏的(de)坐標原點(dian)上(shang)。如果兩塊偏(pian)(pian)(pian)轉(zhuan)板(ban)之(zhi)間存在著(zhu)恒定的(de)電(dian)(dian)位差(cha)，則偏(pian)(pian)(pian)轉(zhuan)板(ban)間就形成一(yi)個(ge)(ge)電(dian)(dian)場，這(zhe)(zhe)個(ge)(ge)電(dian)(dian)場與電(dian)(dian)子(zi)的(de)運動(dong)方向(xiang)(xiang)相垂直(zhi)，于(yu)是(shi)電(dian)(dian)子(zi)就朝(chao)著(zhu)電(dian)(dian)位比較(jiao)高的(de)偏(pian)(pian)(pian)轉(zhuan)板(ban)偏(pian)(pian)(pian)轉(zhuan)。這(zhe)(zhe)樣，在兩偏(pian)(pian)(pian)轉(zhuan)板(ban)之(zhi)間的(de)空間，電(dian)(dian)子(zi)就沿(yan)著(zhu)拋物(wu)線在這(zhe)(zhe)一(yi)點(dian)上(shang)做切線運動(dong)。最后，電(dian)(dian)子(zi)降落在熒光屏上(shang)的(de)A點(dian)，這(zhe)(zhe)個(ge)(ge)A點(dian)距(ju)離(li)熒光屏原點(dian)（0）有一(yi)段(duan)距(ju)離(li)，這(zhe)(zhe)段(duan)距(ju)離(li)稱為偏(pian)(pian)(pian)轉(zhuan)量(liang)，用y表示。偏(pian)(pian)(pian)轉(zhuan)量(liang)y與偏(pian)(pian)(pian)轉(zhuan)板(ban)上(shang)所加(jia)的(de)電(dian)(dian)壓(ya)Vy成正比。同理，在水(shui)平(ping)偏(pian)(pian)(pian)轉(zhuan)板(ban)上(shang)加(jia)有直(zhi)流電(dian)(dian)壓(ya)時，也(ye)發生類似(si)情況(kuang)，只是(shi)光點(dian)在水(shui)平(ping)方向(xiang)(xiang)上(shang)偏(pian)(pian)(pian)轉(zhuan)。
（3）熒(ying)光屏示波器實物圖
熒(ying)(ying)(ying)光(guang)(guang)(guang)屏位(wei)于(yu)示(shi)波(bo)(bo)管的(de)終端(duan)，它的(de)作用是將(jiang)偏轉后的(de)電(dian)(dian)子束顯(xian)示(shi)出(chu)來(lai)，以(yi)便觀察。在(zai)(zai)示(shi)波(bo)(bo)器的(de)熒(ying)(ying)(ying)光(guang)(guang)(guang)屏內(nei)壁涂有一層發光(guang)(guang)(guang)物質(zhi)，因而(er)，熒(ying)(ying)(ying)光(guang)(guang)(guang)屏上(shang)受到(dao)高速(su)電(dian)(dian)子沖(chong)擊的(de)地(di)點就(jiu)顯(xian)現出(chu)熒(ying)(ying)(ying)光(guang)(guang)(guang)。此時(shi)光(guang)(guang)(guang)點的(de)亮度決(jue)定于(yu)電(dian)(dian)子束的(de)數目、密度及其速(su)度。改(gai)變(bian)控(kong)制極的(de)電(dian)(dian)壓時(shi)，電(dian)(dian)子束中電(dian)(dian)子的(de)數目將(jiang)隨之改(gai)變(bian)，光(guang)(guang)(guang)點亮度也就(jiu)改(gai)變(bian)。在(zai)(zai)使(shi)用示(shi)波(bo)(bo)器時(shi)，不宜讓很亮的(de)光(guang)(guang)(guang)點固定出(chu)現在(zai)(zai)示(shi)波(bo)(bo)管熒(ying)(ying)(ying)光(guang)(guang)(guang)屏一個位(wei)置上(shang)，否則該點熒(ying)(ying)(ying)光(guang)(guang)(guang)物質(zhi)將(jiang)因長(chang)期受電(dian)(dian)子沖(chong)擊而(er)燒壞(huai)，從而(er)失去發光(guang)(guang)(guang)能(neng)力。
涂有不(bu)同(tong)熒(ying)光(guang)物質(zhi)的(de)(de)(de)(de)熒(ying)光(guang)屏，在受電子沖擊(ji)時(shi)將顯(xian)示(shi)出(chu)不(bu)同(tong)的(de)(de)(de)(de)顏(yan)色(se)(se)和不(bu)同(tong)的(de)(de)(de)(de)余(yu)(yu)輝時(shi)間，通(tong)常(chang)供(gong)(gong)觀察一般(ban)信(xin)號波(bo)形用的(de)(de)(de)(de)是發(fa)綠光(guang)的(de)(de)(de)(de)，屬(shu)中余(yu)(yu)輝示(shi)波(bo)管(guan)，供(gong)(gong)觀察非周(zhou)期性及低頻信(xin)號用的(de)(de)(de)(de)是發(fa)橙黃(huang)色(se)(se)光(guang)的(de)(de)(de)(de)，屬(shu)長余(yu)(yu)輝示(shi)波(bo)管(guan)；供(gong)(gong)照相用的(de)(de)(de)(de)示(shi)波(bo)器中，一般(ban)都采用發(fa)藍(lan)色(se)(se)的(de)(de)(de)(de)短余(yu)(yu)輝示(shi)波(bo)管(guan)。
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