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示波器的基本原理-顯示電路
顯示(shi)電路包括示(shi)波管(guan)(guan)及其控制電路兩個(ge)(ge)部(bu)分。示(shi)波管(guan)(guan)是一種特殊的電子(zi)管(guan)(guan)，是示(shi)波器一個(ge)(ge)重要組成(cheng)部(bu)分。示(shi)波管(guan)(guan)由電子(zi)槍、偏轉系統和熒光屏(ping)3個(ge)(ge)部(bu)分組成(cheng)。
（1）電子槍
電子(zi)槍(qiang)用于產生并(bing)形(xing)成(cheng)高速(su)、聚束的電子(zi)流(liu)，去轟擊(ji)熒(ying)光屏使之發光。它(ta)主(zhu)要由(you)燈絲F、陰(yin)極(ji)K、控制極(ji)G、第一陽(yang)極(ji)A1、第二陽(yang)極(ji)A2組成(cheng)。除燈絲外(wai)，其余電極(ji)的結構都為(wei)金屬圓(yuan)筒，且它(ta)們(men)的軸(zhou)心(xin)都保持在(zai)同(tong)一軸(zhou)線上。陰(yin)極(ji)被加熱后(hou)，可沿軸(zhou)向發射(she)電子(zi)；控制極(ji)相對(dui)陰(yin)極(ji)來說(shuo)是負電位(wei)，改變電位(wei)可以改變通過控制極(ji)小孔的電子(zi)數目(mu)，也(ye)就是控制熒(ying)光屏上光點的亮(liang)度。為(wei)了提高屏上光點亮(liang)度，又不降低對(dui)電子(zi)束偏轉(zhuan)的靈敏度，現(xian)代(dai)示波管中，在(zai)偏轉(zhuan)系(xi)統和(he)熒(ying)光屏之間還加上一個(ge)后(hou)加速(su)電極(ji)A3。
第(di)(di)(di)(di)一陽(yang)極(ji)對陰極(ji)而言加有(you)(you)約幾百伏的(de)(de)(de)(de)正電(dian)(dian)壓。在(zai)第(di)(di)(di)(di)二(er)(er)(er)陽(yang)極(ji)上(shang)加有(you)(you)一個(ge)(ge)比第(di)(di)(di)(di)一陽(yang)極(ji)更高的(de)(de)(de)(de)正電(dian)(dian)壓。穿過控制極(ji)小(xiao)孔的(de)(de)(de)(de)電(dian)(dian)子(zi)束(shu)，在(zai)第(di)(di)(di)(di)一陽(yang)極(ji)和(he)第(di)(di)(di)(di)二(er)(er)(er)陽(yang)*電(dian)(dian)位(wei)的(de)(de)(de)(de)作(zuo)用(yong)下，得到加速，向熒(ying)光屏(ping)方向作(zuo)高速運動。由(you)于電(dian)(dian)荷的(de)(de)(de)(de)同性相斥(chi)，電(dian)(dian)子(zi)束(shu)會逐(zhu)漸(jian)散(san)開。通過第(di)(di)(di)(di)一陽(yang)極(ji)、第(di)(di)(di)(di)二(er)(er)(er)陽(yang)極(ji)之(zhi)間(jian)電(dian)(dian)場(chang)的(de)(de)(de)(de)聚(ju)(ju)焦(jiao)作(zuo)用(yong)，使(shi)(shi)電(dian)(dian)子(zi)重新聚(ju)(ju)集(ji)起來(lai)并交匯于一點。適當(dang)控制第(di)(di)(di)(di)一陽(yang)極(ji)和(he)第(di)(di)(di)(di)二(er)(er)(er)陽(yang)極(ji)之(zhi)間(jian)電(dian)(dian)位(wei)差的(de)(de)(de)(de)大(da)小(xiao)，便能使(shi)(shi)焦(jiao)點剛好落在(zai)熒(ying)光屏(ping)上(shang)，顯(xian)現一個(ge)(ge)光亮(liang)細(xi)小(xiao)的(de)(de)(de)(de)圓點。改變第(di)(di)(di)(di)一陽(yang)極(ji)和(he)第(di)(di)(di)(di)二(er)(er)(er)陽(yang)極(ji)之(zhi)間(jian)的(de)(de)(de)(de)電(dian)(dian)位(wei)差，可(ke)起調節(jie)光點聚(ju)(ju)焦(jiao)的(de)(de)(de)(de)作(zuo)用(yong)，這(zhe)(zhe)就(jiu)是示波(bo)器(qi)的(de)(de)(de)(de)“聚(ju)(ju)焦(jiao)"和(he)“輔助聚(ju)(ju)焦(jiao)"調節(jie)的(de)(de)(de)(de)原理。第(di)(di)(di)(di)三(san)陽(yang)極(ji)是示波(bo)管錐(zhui)體(ti)內部涂(tu)上(shang)一層石墨形成(cheng)的(de)(de)(de)(de)，通常加有(you)(you)很高的(de)(de)(de)(de)電(dian)(dian)壓，它有(you)(you)三(san)個(ge)(ge)作(zuo)用(yong)：①使(shi)(shi)穿過偏轉系統以后的(de)(de)(de)(de)電(dian)(dian)子(zi)進一步加速，使(shi)(shi)電(dian)(dian)子(zi)有(you)(you)足夠的(de)(de)(de)(de)能量去轟擊(ji)熒(ying)光屏(ping)，以獲得足夠的(de)(de)(de)(de)亮(liang)度；②石墨層涂(tu)在(zai)整個(ge)(ge)錐(zhui)體(ti)上(shang)，能起到屏(ping)蔽作(zuo)用(yong)；③電(dian)(dian)子(zi)束(shu)轟擊(ji)熒(ying)光屏(ping)會產生(sheng)二(er)(er)(er)次電(dian)(dian)子(zi)，處于高電(dian)(dian)位(wei)的(de)(de)(de)(de)A3可(ke)吸收這(zhe)(zhe)些電(dian)(dian)子(zi)。
(2)偏轉系統
示波管的(de)(de)偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)系(xi)統(tong)大都是靜電(dian)偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)式，它由(you)兩對相互垂(chui)直的(de)(de)平行金(jin)屬(shu)板(ban)(ban)組(zu)成，分別稱為水(shui)平偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)和(he)垂(chui)直偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)。分別控制電(dian)子束(shu)在(zai)(zai)水(shui)平方向和(he)垂(chui)直方向的(de)(de)運動。當電(dian)子在(zai)(zai)偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)之間運動時，如果偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)上沒(mei)有加電(dian)壓，偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)之間無(wu)電(dian)場(chang)，離開第二陽極(ji)后進(jin)(jin)入偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)系(xi)統(tong)的(de)(de)電(dian)子將沿軸向運動，射(she)向屏幕(mu)的(de)(de)中心。如果偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)上有電(dian)壓，偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)板(ban)(ban)之間則(ze)有電(dian)場(chang)，進(jin)(jin)入偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)系(xi)統(tong)的(de)(de)電(dian)子會在(zai)(zai)偏(pian)(pian)轉(zhuan)(zhuan)(zhuan)電(dian)場(chang)的(de)(de)作用下射(she)向熒光屏的(de)(de)定位置。
如果(guo)兩(liang)塊偏(pian)轉(zhuan)(zhuan)板(ban)(ban)互相(xiang)平行(xing)，并且它們(men)的(de)(de)電(dian)(dian)(dian)(dian)位差等(deng)于零，那么通(tong)過(guo)偏(pian)轉(zhuan)(zhuan)板(ban)(ban)空間的(de)(de)，具有速度υ的(de)(de)電(dian)(dian)(dian)(dian)子(zi)(zi)束就(jiu)會沿著原方(fang)向(xiang)（設為(wei)軸(zhou)線方(fang)向(xiang)）運動，并打(da)在熒(ying)光(guang)屏的(de)(de)坐(zuo)標原點(dian)(dian)(dian)上(shang)(shang)(shang)。如果(guo)兩(liang)塊偏(pian)轉(zhuan)(zhuan)板(ban)(ban)之(zhi)間存(cun)在著恒定的(de)(de)電(dian)(dian)(dian)(dian)位差，則偏(pian)轉(zhuan)(zhuan)板(ban)(ban)間就(jiu)形(xing)成一(yi)(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)場，這(zhe)(zhe)個(ge)(ge)電(dian)(dian)(dian)(dian)場與電(dian)(dian)(dian)(dian)子(zi)(zi)的(de)(de)運動方(fang)向(xiang)相(xiang)垂直(zhi)，于是電(dian)(dian)(dian)(dian)子(zi)(zi)就(jiu)朝著電(dian)(dian)(dian)(dian)位比較(jiao)高(gao)的(de)(de)偏(pian)轉(zhuan)(zhuan)板(ban)(ban)偏(pian)轉(zhuan)(zhuan)。這(zhe)(zhe)樣(yang)，在兩(liang)偏(pian)轉(zhuan)(zhuan)板(ban)(ban)之(zhi)間的(de)(de)空間，電(dian)(dian)(dian)(dian)子(zi)(zi)就(jiu)沿著拋物線在這(zhe)(zhe)一(yi)(yi)點(dian)(dian)(dian)上(shang)(shang)(shang)做(zuo)切線運動。最后(hou)，電(dian)(dian)(dian)(dian)子(zi)(zi)降落在熒(ying)光(guang)屏上(shang)(shang)(shang)的(de)(de)A點(dian)(dian)(dian)，這(zhe)(zhe)個(ge)(ge)A點(dian)(dian)(dian)距(ju)離(li)熒(ying)光(guang)屏原點(dian)(dian)(dian)（0）有一(yi)(yi)段(duan)(duan)距(ju)離(li)，這(zhe)(zhe)段(duan)(duan)距(ju)離(li)稱為(wei)偏(pian)轉(zhuan)(zhuan)量，用y表(biao)示。偏(pian)轉(zhuan)(zhuan)量y與偏(pian)轉(zhuan)(zhuan)板(ban)(ban)上(shang)(shang)(shang)所(suo)加(jia)(jia)的(de)(de)電(dian)(dian)(dian)(dian)壓Vy成正比。同理，在水平偏(pian)轉(zhuan)(zhuan)板(ban)(ban)上(shang)(shang)(shang)加(jia)(jia)有直(zhi)流電(dian)(dian)(dian)(dian)壓時，也發生(sheng)類似情況(kuang)，只是光(guang)點(dian)(dian)(dian)在水平方(fang)向(xiang)上(shang)(shang)(shang)偏(pian)轉(zhuan)(zhuan)。
（3）熒光(guang)屏示(shi)波器(qi)實(shi)物圖
熒(ying)光屏(ping)位于示(shi)波管的(de)(de)終(zhong)端，它的(de)(de)作用是將偏(pian)轉(zhuan)后的(de)(de)電(dian)(dian)(dian)(dian)子(zi)束(shu)顯示(shi)出(chu)來，以便觀察。在(zai)示(shi)波器的(de)(de)熒(ying)光屏(ping)內(nei)壁涂有一層發光物(wu)質，因而，熒(ying)光屏(ping)上(shang)受到高速電(dian)(dian)(dian)(dian)子(zi)沖擊的(de)(de)地點(dian)(dian)就(jiu)(jiu)顯現(xian)出(chu)熒(ying)光。此時(shi)光點(dian)(dian)的(de)(de)亮度決定于電(dian)(dian)(dian)(dian)子(zi)束(shu)的(de)(de)數目(mu)、密度及其速度。改(gai)變(bian)控制極的(de)(de)電(dian)(dian)(dian)(dian)壓時(shi)，電(dian)(dian)(dian)(dian)子(zi)束(shu)中(zhong)電(dian)(dian)(dian)(dian)子(zi)的(de)(de)數目(mu)將隨(sui)之改(gai)變(bian)，光點(dian)(dian)亮度也(ye)就(jiu)(jiu)改(gai)變(bian)。在(zai)使用示(shi)波器時(shi)，不宜讓很亮的(de)(de)光點(dian)(dian)固定出(chu)現(xian)在(zai)示(shi)波管熒(ying)光屏(ping)一個位置上(shang)，否則(ze)該點(dian)(dian)熒(ying)光物(wu)質將因長期受電(dian)(dian)(dian)(dian)子(zi)沖擊而燒壞，從而失去發光能力(li)。
涂(tu)有(you)不同(tong)熒(ying)光(guang)物質的(de)熒(ying)光(guang)屏，在受電子沖擊時將顯(xian)示(shi)出不同(tong)的(de)顏色(se)和不同(tong)的(de)余(yu)輝(hui)(hui)時間，通常供觀察一般(ban)信號波(bo)形用(yong)的(de)是(shi)發(fa)綠光(guang)的(de)，屬中余(yu)輝(hui)(hui)示(shi)波(bo)管(guan)，供觀察非(fei)周(zhou)期性及(ji)低(di)頻(pin)信號用(yong)的(de)是(shi)發(fa)橙(cheng)黃(huang)色(se)光(guang)的(de)，屬長余(yu)輝(hui)(hui)示(shi)波(bo)管(guan)；供照(zhao)相(xiang)用(yong)的(de)示(shi)波(bo)器(qi)中，一般(ban)都采用(yong)發(fa)藍色(se)的(de)短余(yu)輝(hui)(hui)示(shi)波(bo)管(guan)。
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