? ? 【城銘科技】采用(yong)常規的(de)可(ke)見光照明，不僅不能(neng)(neng)(neng)隱蔽，反而更(geng)加暴露監(jian)(jian)控(kong)目(mu)標，在居(ju)民小區(qu)還有(you)擾民問題。隱蔽的(de)夜視監(jian)(jian)控(kong)，目(mu)前都是采用(yong)紅(hong)(hong)外(wai)攝像技術(shu)(shu)。紅(hong)(hong)外(wai)攝像技術(shu)(shu)分為被動紅(hong)(hong)外(wai)攝像技術(shu)(shu)和主(zhu)動紅(hong)(hong)外(wai)攝像技術(shu)(shu)。在夜視系(xi)統中(zhong)經(jing)常采用(yong)主(zhu)動紅(hong)(hong)外(wai)攝像技術(shu)(shu)， 即采用(yong)紅(hong)(hong)外(wai)輻(fu)射(she)“照明”，產生人眼看(kan)不見而普通攝像機(ji)能(neng)(neng)(neng)捕捉到的(de)紅(hong)(hong)外(wai)光，輻(fu)射(she)“照明”景物(wu)和環境。夜間(jian)監(jian)(jian)控(kong)中(zhong)，選擇使用(yong)合適的(de)紅(hong)(hong)外(wai)燈才(cai)能(neng)(neng)(neng)獲得到良好的(de)監(jian)(jian)控(kong)效果。
紅(hong)外(wai)(wai)燈(deng)的(de)選擇最重要的(de)問(wen)題是(shi)成套性(xing)，即紅(hong)外(wai)(wai)燈(deng)與攝(she)像(xiang)機、鏡頭(tou)、防護(hu)罩、供電電源等的(de)成套性(xing)。在(zai)設(she)計方案時(shi)對所有器材(cai)綜合考(kao)(kao)(kao)慮設(she)計，把它作為一個紅(hong)外(wai)(wai)低照度夜視(shi)監控(kong)系(xi)統(tong)工程來考(kao)(kao)(kao)慮設(she)計。有的(de)人(ren)買完了攝(she)像(xiang)機、鏡頭(tou)、防護(hu)罩、電源之后甚至(zhi)安裝之后才(cai)去考(kao)(kao)(kao)慮購買紅(hong)外(wai)(wai)燈(deng)，這是(shi)不正確的(de)，在(zai)考(kao)(kao)(kao)慮成套性(xing)時(shi)，特別要注意(yi)以下幾個問(wen)題。
一(yi)、用(yong)黑(hei)白攝像(xiang)機或特殊彩色攝像(xiang)機
CCD 圖(tu)像(xiang)傳感(gan)(gan)器(qi)具有很寬的感(gan)(gan)光(guang)光(guang)譜(pu)范(fan)圍，其(qi)感(gan)(gan)光(guang)光(guang)譜(pu)不但包括可(ke)見光(guang)區(qu)域(yu)(yu)，還延長到紅外(wai)區(qu)域(yu)(yu)，利用此特性，可(ke)以在夜間無可(ke)見光(guang)照(zhao)明的情況下，用輔助紅外(wai)光(guang)源照(zhao)明也可(ke)使CCD圖(tu)像(xiang)傳感(gan)(gan)器(qi)清晰的成像(xiang)。而普通彩(cai)(cai)色(se)(se)攝像(xiang)機為了(le)能傳輸(shu)(shu)彩(cai)(cai)色(se)(se)信(xin)(xin)號(hao)，從 CCD器(qi)件(jian)的輸(shu)(shu)出(chu)信(xin)(xin)號(hao)中分離出(chu)綠藍紅三(san)種基(ji)色(se)(se)視頻(pin)信(xin)(xin)號(hao)，然后合成彩(cai)(cai)色(se)(se)電視信(xin)(xin)號(hao)，其(qi)感(gan)(gan)光(guang)光(guang)譜(pu)只在可(ke)見光(guang)區(qu)域(yu)(yu)。
隨著技術的進步出現(xian)白(bai)天(tian)彩色(se)(se)/晚上黑(hei)白(bai)攝像(xiang)(xiang)機(ji)， 它采(cai)用兩個 CCD進行切(qie)換或采(cai)用一(yi)個CCD 利用數字電路的切(qie)換來實現(xian)，但是存在黑(hei)白(bai)照度偏高(gao)(gao)、有的對彩色(se)(se)色(se)(se)彩的不(bu)利影響等缺點。而紅外(wai)低(di)照度彩色(se)(se)攝像(xiang)(xiang)機(ji)紅外(wai)感度比一(yi)般攝像(xiang)(xiang)機(ji)高(gao)(gao) 4 倍以上，隨著成本的降低(di)，會成為發展趨勢的。
二、要求選用(yong)低照度(du)攝像機
攝像(xiang)(xiang)機(ji)的(de)最低(di)照度(du)(du)是(shi)當被(bei)攝景(jing)物(wu)的(de)光亮度(du)(du)低(di)到一定(ding)程度(du)(du)而使攝像(xiang)(xiang)機(ji)輸出的(de)視頻信號(hao)電平(ping)低(di)到某一規定(ding)值時(shi)的(de)景(jing)物(wu)光亮度(du)(du)值。測(ce)定(ding)此(ci)參數時(shi)，還應特別注明鏡頭的(de)光圈 F的(de)大小。
例如(ru)使(shi)用 F1.2 的(de)(de)(de)(de)(de)(de)鏡頭，當(dang)(dang)被攝(she)(she)影(ying)景物(wu)的(de)(de)(de)(de)(de)(de)照(zhao)(zhao)(zhao)度(du)(du)(du)值(zhi)(zhi)低(di)(di)到 0.02Lux 時，攝(she)(she)像(xiang)(xiang)(xiang)機(ji)輸出的(de)(de)(de)(de)(de)(de)視頻信(xin)號幅(fu)值(zhi)(zhi)為(wei)標(biao)準幅(fu)值(zhi)(zhi) 700mv 的(de)(de)(de)(de)(de)(de) 50%-33%，則稱此攝(she)(she)像(xiang)(xiang)(xiang)機(ji)的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)為(wei) 0.02Lux/F1.2。有的(de)(de)(de)(de)(de)(de)攝(she)(she)像(xiang)(xiang)(xiang)機(ji)生(sheng)產(chan)廠(chang)家給出不同光(guang)圈 F 時的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)。當(dang)(dang)選擇攝(she)(she)像(xiang)(xiang)(xiang)機(ji)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)高(gao)于紅外(wai)燈(deng)(deng)要求時，紅外(wai)燈(deng)(deng)的(de)(de)(de)(de)(de)(de)有效距離將受到一(yi)定影(ying)響。 應當(dang)(dang)提醒用戶的(de)(de)(de)(de)(de)(de)是(shi)市(shi)場(chang)(chang)上(shang)出售的(de)(de)(de)(de)(de)(de)攝(she)(she)像(xiang)(xiang)(xiang)機(ji)技術(shu)性能標(biao)出的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)有兩種(zhong)不正常情(qing)況，一(yi)種(zhong)是(shi)攝(she)(she)像(xiang)(xiang)(xiang)機(ji)制(zhi)造商所(suo)標(biao)的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)是(shi)所(suo)謂(wei)的(de)(de)(de)(de)(de)(de)靶面照(zhao)(zhao)(zhao)度(du)(du)(du)，即 CCD圖像(xiang)(xiang)(xiang)傳感器上(shang)的(de)(de)(de)(de)(de)(de)光(guang)照(zhao)(zhao)(zhao)度(du)(du)(du)，? 它比景物(wu)照(zhao)(zhao)(zhao)度(du)(du)(du)低(di)(di) 10 倍左右(you)(you)；另一(yi)種(zhong)是(shi)有個(ge)別攝(she)(she)像(xiang)(xiang)(xiang)機(ji)制(zhi)造商或銷售商虛報最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)。目(mu)前市(shi)場(chang)(chang)上(shang)比較經濟的(de)(de)(de)(de)(de)(de)黑白攝(she)(she)像(xiang)(xiang)(xiang)機(ji)，有的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)標(biao)為(wei) 0.01～0.02lux，它們的(de)(de)(de)(de)(de)(de)實(shi)際(ji)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)僅為(wei) 0.1～0.2Lux，如(ru)果，使(shi)用的(de)(de)(de)(de)(de)(de)紅外(wai)燈(deng)(deng)要求攝(she)(she)像(xiang)(xiang)(xiang)機(ji)的(de)(de)(de)(de)(de)(de)最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du)為(wei)0.02Lux，必然影(ying)響紅外(wai)燈(deng)(deng)的(de)(de)(de)(de)(de)(de)有效照(zhao)(zhao)(zhao)射距離，而(er)購買最(zui)(zui)(zui)(zui)(zui)低(di)(di)照(zhao)(zhao)(zhao)度(du)(du)(du) 0.02Lux 的(de)(de)(de)(de)(de)(de)攝(she)(she)像(xiang)(xiang)(xiang)機(ji)，價格可能比 0.1～0.2Lux 攝(she)(she)像(xiang)(xiang)(xiang)機(ji)最(zui)(zui)(zui)(zui)(zui)少高(gao)一(yi)倍左右(you)(you)。
三、要求攝像機(ji)的尺寸規(gui)格
攝(she)(she)像(xiang)(xiang)機(ji)(ji)標稱(cheng)尺(chi)寸日趨小(xiao)型化(hua)，目(mu)前市場上的攝(she)(she)像(xiang)(xiang)機(ji)(ji)尺(chi)寸規格有(you) 1/2“、1/3”、1/4“，攝(she)(she)像(xiang)(xiang)機(ji)(ji)尺(chi)寸大，接(jie)收的光通(tong)量(liang)大，攝(she)(she)像(xiang)(xiang)機(ji)(ji)尺(chi)寸小(xiao)，接(jie)受的光通(tong)量(liang)少(shao)，如紅外(wai)燈標稱(cheng)的有(you)效(xiao)距(ju)離是1/2”攝(she)(she)像(xiang)(xiang)機(ji)(ji)條件下(xia)試驗的，如采用 1/3“或者 1/4”攝(she)(she)像(xiang)(xiang)機(ji)(ji)，有(you)效(xiao)距(ju)離也將受到一定影響。1/3“攝(she)(she)像(xiang)(xiang)機(ji)(ji)光通(tong)量(liang)只有(you) 1/2”攝(she)(she)像(xiang)(xiang)機(ji)(ji)光通(tong)量(liang)的 44%。
四、鏡頭的尺寸規格
與攝像機的尺(chi)寸(cun)規格(ge)同理，不(bu)再贅述。需(xu)要(yao)注意(yi)的是紅外光源(yuan)由于波長長，反映到(dao)普通非紅外鏡頭上會比可(ke)見光焦(jiao)點略深一(yi)些，所以在(zai)用(yong)了紅外燈夜(ye)間成像時，會感覺焦(jiao)距稍微模糊一(yi)點。
五、攝像機和鏡頭的(de)功(gong)能要求
攝像機有(you)自動(dong)電子快門功能，AGC 自動(dong)增益控制功能，鏡頭有(you)自動(dong)光圈，以適(shi)應晝夜照度(du)很大的變化。
六、電源供應
電(dian)(dian)(dian)(dian)(dian)視(shi)監控(kong)(kong)系統(tong)前端設備的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源供(gong)(gong)應要統(tong)一考慮(lv)設計。紅(hong)外(wai)(wai)燈(deng)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源供(gong)(gong)應，考慮(lv)到紅(hong)外(wai)(wai)管的(de)(de)(de)(de)工(gong)作電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)對供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)十分(fen)敏感，而電(dian)(dian)(dian)(dian)(dian)纜(lan)長度不(bu)同對直(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)衰(shuai)減不(bu)同。在多個紅(hong)外(wai)(wai)燈(deng)距(ju)控(kong)(kong)制室的(de)(de)(de)(de)距(ju)離相差較(jiao)大時(shi)，采(cai)用 DC12V集中(zhong)供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)可能使(shi)距(ju)控(kong)(kong)制室近的(de)(de)(de)(de)紅(hong)外(wai)(wai)燈(deng)供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)高，距(ju)控(kong)(kong)制室遠的(de)(de)(de)(de)紅(hong)外(wai)(wai)燈(deng)供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)。加(jia)之電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)調整上(shang)的(de)(de)(de)(de)偏差，可能造(zao)成電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)過高的(de)(de)(de)(de)紅(hong)外(wai)(wai)燈(deng)壽命縮短甚(shen)至燒壞，電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)的(de)(de)(de)(de)紅(hong)外(wai)(wai)燈(deng)發射功率不(bu)足。因此建議(yi)盡可能采(cai)用 AC22V供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)或配一對一的(de)(de)(de)(de)直(zhi)流(liu)(liu)穩(wen)壓(ya)(ya)電(dian)(dian)(dian)(dian)(dian)源，這種直(zhi)流(liu)(liu)穩(wen)壓(ya)(ya)電(dian)(dian)(dian)(dian)(dian)源有的(de)(de)(de)(de)在電(dian)(dian)(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)波動在 AC100V-245V時(shi)輸出直(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)都(dou)是穩(wen)定的(de)(de)(de)(de)，保證紅(hong)外(wai)(wai)燈(deng)紅(hong)外(wai)(wai)輻射功率都(dou)是穩(wen)定可靠的(de)(de)(de)(de)。
防護罩對紅外燈(deng)的效果(guo)也(ye)有(you)影(ying)響，紅外光在傳輸(shu)過(guo)程中(zhong)，通過(guo)不同(tong)介質，透射率和(he)反射率也(ye)不同(tong)。不同(tong)的視窗玻(bo)璃(li)，特別是自(zi)動除霜鍍(du)膜玻(bo)璃(li)，對紅外光的衰減也(ye)不同(tong)。
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