干擾源類型及對控制板系統的干擾

1. 來自空間的輻射干擾

空間的輻射(she)電(dian)磁(ci)場主要(yao)來自電(dian)力(li)網(wang)絡、雷(lei)電(dian)、無線(xian)電(dian)廣播、電(dian)視(shi)、雷(lei)達(da)、高頻(pin)(pin)感應加熱設(she)備(bei)，其分布極為復雜。若控制(zhi)板(ban)系統(tong)置于所射(she)頻(pin)(pin)場內。就會受到輻射(she)干擾，其影響主要(yao)通過兩條路徑:一(yi)是對控制(zhi)板(ban)通信(xin)網(wang)絡的輻射(she)，由通信(xin)線(xian)路的感應引人干擾;二(er)是直接對控制(zhi)板(ban)內部的輻射(she)，由電(dian)路感應產生(sheng)干擾。

2. 來自系統外引線的干擾

a. 來自電源的干擾

控制(zhi)板系統的正常供(gong)電(dian)(dian)電(dian)(dian)源均由電(dian)(dian)網供(gong)電(dian)(dian)。由于電(dian)(dian)網覆蓋范圍(wei)廣，它將受到所有空間電(dian)(dian)磁干(gan)擾而在線路上感應出電(dian)(dian)壓和電(dian)(dian)流。尤其(qi)是電(dian)(dian)網內部(bu)的變化，開關操(cao)作(zuo)浪涌(yong)、大型電(dian)(dian)力設備起(qi)停、電(dian)(dian)網短路暫態沖擊(ji)等，都通過輸電(dian)(dian)線路傳(chuan)到電(dian)(dian)源。控制(zhi)板電(dian)(dian)源通常采用隔離(li)電(dian)(dian)源，但其(qi)機構及(ji)制(zhi)造工藝因素使其(qi)隔離(li)性并不理想。

b. 來自信號線引入的干擾

控制(zhi)板(ban)系統連(lian)接的(de)(de)各類信(xin)(xin)號(hao)傳(chuan)輸線，除了(le)傳(chuan)輸有效(xiao)的(de)(de)各類信(xin)(xin)息之外，總會(hui)有外部干(gan)擾信(xin)(xin)號(hao)侵入。此(ci)干(gan)擾主要有兩種途(tu)徑:一是(shi)通過變送器供電電源或(huo)共用信(xin)(xin)號(hao)儀表(biao)的(de)(de)供電電源串(chuan)入的(de)(de)電網干(gan)擾;二是(shi)信(xin)(xin)號(hao)線受空間(jian)電磁輻(fu)射感(gan)應的(de)(de)干(gan)擾，即(ji)信(xin)(xin)號(hao)線上的(de)(de)外部感(gan)應干(gan)擾，這(zhe)是(shi)很(hen)嚴(yan)重的(de)(de)。由信(xin)(xin)號(hao)引(yin)入干(gan)擾會(hui)引(yin)起(qi)vo信(xin)(xin)號(hao)工作異常(chang)和(he)測量精度的(de)(de)降低(di)，嚴(yan)重時將引(yin)起(qi)元(yuan)器件損傷。對于隔離(li)性能差(cha)的(de)(de)系統，還將導致(zhi)信(xin)(xin)號(hao)間(jian)互相干(gan)擾，引(yin)起(qi)共地系統總線回(hui)流，造成邏輯數據變化、誤動和(he)死機。

c. 來自接地系統混亂時的干擾

接(jie)(jie)地(di)是提高電(dian)(dian)(dian)(dian)子(zi)設備(bei)電(dian)(dian)(dian)(dian)磁(ci)(ci)兼(jian)容(rong)性的(de)有效手段之一。正確地(di)接(jie)(jie)地(di)，既能(neng)抑(yi)制電(dian)(dian)(dian)(dian)磁(ci)(ci)干(gan)(gan)擾(rao)的(de)影(ying)響(xiang)(xiang)，又能(neng)抑(yi)制設備(bei)向外(wai)發出干(gan)(gan)擾(rao);而錯(cuo)誤的(de)接(jie)(jie)地(di)，反而會(hui)(hui)引(yin)(yin)入嚴重的(de)干(gan)(gan)擾(rao)信(xin)號(hao)，使(shi)控(kong)制板系(xi)統(tong)將無法(fa)正常工作(zuo)。接(jie)(jie)地(di)系(xi)統(tong)混亂對控(kong)制板系(xi)統(tong)的(de)干(gan)(gan)擾(rao)主要是各個接(jie)(jie)地(di)點電(dian)(dian)(dian)(dian)位(wei)(wei)分布(bu)不(bu)(bu)均，不(bu)(bu)同接(jie)(jie)地(di)點間(jian)存在地(di)電(dian)(dian)(dian)(dian)位(wei)(wei)差，引(yin)(yin)起(qi)地(di)環路(lu)電(dian)(dian)(dian)(dian)流(liu)，影(ying)響(xiang)(xiang)系(xi)統(tong)正常工作(zuo)。例(li)如電(dian)(dian)(dian)(dian)纜屏(ping)蔽(bi)(bi)層(ceng)必須一點接(jie)(jie)地(di)，如果電(dian)(dian)(dian)(dian)纜屏(ping)蔽(bi)(bi)層(ceng)兩(liang)端都接(jie)(jie)地(di)，就存在地(di)電(dian)(dian)(dian)(dian)位(wei)(wei)差，這時就有電(dian)(dian)(dian)(dian)流(liu)流(liu)過屏(ping)蔽(bi)(bi)層(ceng)，當發生異常狀(zhuang)態如雷(lei)擊時，地(di)線電(dian)(dian)(dian)(dian)流(liu)將更大。此外(wai)，屏(ping)蔽(bi)(bi)層(ceng)、接(jie)(jie)地(di)線和地(di)之間(jian)有可能(neng)構(gou)成閉合環路(lu)，在變(bian)化磁(ci)(ci)場(chang)的(de)作(zuo)用下，屏(ping)蔽(bi)(bi)層(ceng)內又會(hui)(hui)出現感應電(dian)(dian)(dian)(dian)流(liu)，通過屏(ping)蔽(bi)(bi)層(ceng)與芯線之間(jian)的(de)禍(huo)合，干(gan)(gan)擾(rao)信(xin)號(hao)形成回路(lu)。模擬地(di)電(dian)(dian)(dian)(dian)位(wei)(wei)的(de)分布(bu)將導致測(ce)量精度下降，引(yin)(yin)起(qi)對信(xin)號(hao)測(ce)控(kong)的(de)嚴重失真和誤動作(zuo)。控(kong)制板工作(zuo)的(de)邏(luo)輯(ji)電(dian)(dian)(dian)(dian)壓干(gan)(gan)擾(rao)容(rong)限較低，邏(luo)輯(ji)地(di)電(dian)(dian)(dian)(dian)位(wei)(wei)的(de)分布(bu)干(gan)(gan)擾(rao)容(rong)易影(ying)響(xiang)(xiang)控(kong)制板的(de)邏(luo)輯(ji)運(yun)算和數據存貯，造成數據混亂、程序跑飛或死(si)機。

控制板抗干擾設計的一般方法

抑(yi)制電磁干(gan)擾(rao)(rao)的基本原(yuan)則是抑(yi)制干(gan)擾(rao)(rao)源(yuan)、切斷(duan)或衰(shuai)減電磁干(gan)擾(rao)(rao)的傳播途徑、提高裝置和系統的抗干(gan)擾(rao)(rao)能力。

1. 設備選型

在(zai)選(xuan)擇(ze)設備時(shi)，首(shou)先要選(xuan)擇(ze)有較高抗干(gan)(gan)擾(rao)能力(li)的(de)(de)(de)(de)產(chan)品(pin)，其次還應(ying)(ying)了解(jie)生(sheng)產(chan)廠給出(chu)的(de)(de)(de)(de)抗干(gan)(gan)擾(rao)指標(biao)，如(ru)耐壓(ya)能力(li)、共模抑(yi)制(zhi)比，對最大(da)(da)電(dian)場強(qiang)度和最高頻率(lv)范圍設置。另外考(kao)察(cha)其在(zai)類似工作(zuo)中(zhong)的(de)(de)(de)(de)應(ying)(ying)用(yong)實績。如(ru)果選(xuan)擇(ze)國(guo)外進口(kou)產(chan)品(pin)要注意:我(wo)國(guo)是采用(yong)220v高內(nei)阻(zu)電(dian)網制(zhi)式(shi)，比如(ru)日本(ben)是110v低內(nei)阻(zu)電(dian)網。由于我(wo)國(guo)電(dian)網內(nei)阻(zu)大(da)(da)，零點電(dian)位漂移大(da)(da)，地電(dian)位變化大(da)(da)，工業企業現場的(de)(de)(de)(de)電(dian)磁干(gan)(gan)擾(rao)至少要比日本(ben)高4倍以上，對系統(tong)抗干(gan)(gan)擾(rao)性能要求更高，在(zai)國(guo)外能正常工作(zuo)的(de)(de)(de)(de)控制(zhi)板產(chan)品(pin)在(zai)國(guo)內(nei)工業就不一定能可靠運(yun)行，這就要求在(zai)采用(yong)國(guo)外產(chan)品(pin)時(shi)，按我(wo)國(guo)的(de)(de)(de)(de)標(biao)準((GB/T13926)合理選(xuan)擇(ze)。

2. 設計施工中的抗干擾設計

為保證系統(tong)在工業電磁環境中(zhong)免受或減少內外(wai)電磁干(gan)(gan)擾(rao)(rao)，必須綜合(he)抗(kang)干(gan)(gan)擾(rao)(rao)設(she)計(ji)，在設(she)計(ji)階段(duan)采取措施(shi)。綜合(he)抗(kang)干(gan)(gan)擾(rao)(rao)設(she)計(ji)主要內容包(bao)括:對(dui)控(kong)制板'系統(tong)及外(wai)引(yin)線(xian)進(jin)行屏蔽以(yi)防空間(jian)輻射電磁干(gan)(gan)擾(rao)(rao);對(dui)外(wai)引(yin)線(xian)進(jin)行隔離、濾(lv)波，特(te)別是動力電纜，應該與信號線(xian)分層布置，以(yi)防通過(guo)外(wai)引(yin)線(xian)引(yin)入傳導電磁干(gan)(gan)擾(rao)(rao);正確設(she)計(ji)接地點和接地裝置，完善接地系統(tong)。

主要抗干擾措施

1. 采用性能優良的電源

在控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)中，電(dian)(dian)(dian)源(yuan)(yuan)占有(you)(you)十分重要的地(di)位。電(dian)(dian)(dian)網(wang)干擾串入控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)主要通過控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)的供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)、變送器供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)和(he)與控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)具有(you)(you)直(zhi)接(jie)(jie)(jie)電(dian)(dian)(dian)氣連接(jie)(jie)(jie)的儀(yi)表供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)等藕合進入的。對于(yu)控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)供(gong)電(dian)(dian)(dian)的電(dian)(dian)(dian)源(yuan)(yuan)，一般都采用隔離(li)性(xing)能較好電(dian)(dian)(dian)源(yuan)(yuan);而對于(yu)變送器供(gong)電(dian)(dian)(dian)的電(dian)(dian)(dian)源(yuan)(yuan)和(he)控(kong)制(zhi)(zhi)(zhi)板系(xi)統(tong)有(you)(you)直(zhi)接(jie)(jie)(jie)電(dian)(dian)(dian)氣連接(jie)(jie)(jie)的儀(yi)表的供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)，選擇分布電(dian)(dian)(dian)容小、抑制(zhi)(zhi)(zhi)性(xing)強(qiang)的配(pei)電(dian)(dian)(dian)器，抑制(zhi)(zhi)(zhi)電(dian)(dian)(dian)網(wang)引入的干擾。

2. 電纜選擇和敷設

為了(le)減少動(dong)力電(dian)(dian)纜(lan)(lan)輻(fu)射電(dian)(dian)磁干擾，不(bu)同類型的(de)信(xin)號(hao)分別由不(bu)同電(dian)(dian)纜(lan)(lan)傳輸(shu)，信(xin)號(hao)電(dian)(dian)纜(lan)(lan)應按傳輸(shu)信(xin)號(hao)種類分層敷(fu)設，嚴(yan)禁(jin)用同一電(dian)(dian)纜(lan)(lan)的(de)不(bu)同導(dao)線(xian)同時傳送動(dong)力電(dian)(dian)源和信(xin)號(hao)，避免信(xin)號(hao)線(xian)與動(dong)力電(dian)(dian)纜(lan)(lan)靠近平(ping)行敷(fu)設.以(yi)減少電(dian)(dian)磁干擾。

3. 硬件濾波及軟件抗干擾措施

信(xin)號(hao)在接入計算機前，在信(xin)號(hao)線與地間并(bing)聯電(dian)容，以減少共(gong)模(mo)干(gan)擾。由(you)于電(dian)磁干(gan)擾的(de)復雜性，要(yao)根本消(xiao)除干(gan)擾影響是不可能的(de)，困此在控(kong)制板(ban)系統的(de)軟(ruan)(ruan)件設計和組態時，還(huan)應在軟(ruan)(ruan)件方面進行抗干(gan)擾處(chu)理，進一(yi)步提高系統的(de)可靠性。

4. 選擇正確接地點系統

接(jie)(jie)地(di)(di)(di)(di)的(de)(de)(de)目的(de)(de)(de)通常(chang)有(you)兩個(ge)，其一為了安全，其二是為了抑制(zhi)(zhi)干(gan)擾。完善的(de)(de)(de)接(jie)(jie)地(di)(di)(di)(di)系統(tong)(tong)(tong)(tong)是控(kong)制(zhi)(zhi)板(ban)系統(tong)(tong)(tong)(tong)抗電磁干(gan)擾的(de)(de)(de)重要措(cuo)施(shi)之(zhi)一。系統(tong)(tong)(tong)(tong)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)有(you):浮(fu)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)、直接(jie)(jie)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)和電容(rong)接(jie)(jie)地(di)(di)(di)(di)三種方(fang)(fang)式(shi)(shi)。對(dui)控(kong)制(zhi)(zhi)板(ban)系統(tong)(tong)(tong)(tong)而(er)言，它(ta)屬高速低(di)電平(ping)控(kong)制(zhi)(zhi)裝(zhuang)置(zhi)，應采用(yong)(yong)直接(jie)(jie)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)。由(you)于信號電纜分布電容(rong)和輸入裝(zhuang)置(zhi)濾波等的(de)(de)(de)影響，裝(zhuang)置(zhi)之(zhi)間的(de)(de)(de)信號交換頻率一般都低(di)于l MHz，所以控(kong)制(zhi)(zhi)板(ban)系統(tong)(tong)(tong)(tong)接(jie)(jie)地(di)(di)(di)(di)線采用(yong)(yong)一點(dian)接(jie)(jie)地(di)(di)(di)(di)和串聯一點(dian)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)。集中布置(zhi)的(de)(de)(de)控(kong)制(zhi)(zhi)板(ban)系統(tong)(tong)(tong)(tong)適于并聯一點(dian)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)，各裝(zhuang)置(zhi)的(de)(de)(de)柜體中心(xin)接(jie)(jie)地(di)(di)(di)(di)點(dian)以單獨的(de)(de)(de)接(jie)(jie)地(di)(di)(di)(di)線引向接(jie)(jie)地(di)(di)(di)(di)極。如果(guo)裝(zhuang)置(zhi)間距較大，應采用(yong)(yong)串聯一點(dian)接(jie)(jie)地(di)(di)(di)(di)方(fang)(fang)式(shi)(shi)。

5. 控制板輸入、輸出信號回路采用光電隔離

利用光電禍合(he)器(qi)的開關特性實(shi)現(xian)輸人和輸出(chu)信(xin)(xin)號的完全隔(ge)離(li)，已成(cheng)為抑制干(gan)擾(rao)的有效措施之一。光電輻合(he)器(qi)把各種(zhong)模(mo)擬負載和數(shu)字(zi)信(xin)(xin)息源隔(ge)離(li)開來，也就是把“模(mo)擬的”和“數(shu)字(zi)的”斷開。光電藕合(he)器(qi)能實(shi)現(xian)良好隔(ge)離(li)的原因有三個。

a. 由于光電(dian)棍合器(qi)輸入電(dian)阻(zu)(zu)抗很小而(er)干擾源的內阻(zu)(zu)則很大，因此(ci)分壓到光電(dian)藕(ou)合器(qi)輸入端(duan)的干擾信號較小，輸入回(hui)路與輸出回(hui)路之間分布(bu)電(dian)容(rong)極小，而(er)且絕(jue)緣電(dian)阻(zu)(zu)較高，因此(ci)回(hui)路一邊(bian)的干擾很難通過光電(dian)藕(ou)合的回(hui)饋送到另一邊(bian);

b. 光(guang)電藕合器在密封條件下實現輸入回路(lu)與輸出回路(lu)的光(guang)禍合，不會(hui)受外(wai)界光(guang)的影響;

c. 無論是模擬還是數(shu)字信(xin)(xin)號(hao)，在(zai)輸(shu)入(ru)、輸(shu)出通道上都采用(yong)光電禍合(he)電路(lu)，用(yong)光線來藕(ou)合(he)信(xin)(xin)號(hao)，使輸(shu)人、輸(shu)出沒(mei)有電的直接聯系(xi)，可(ke)以有效(xiao)地防止漏電、短(duan)路(lu)、打火、感應引起的過電壓串(chuan)入(ru)控(kong)制(zhi)板系(xi)統(tong)(tong)(tong)。因(yin)此在(zai)控(kong)制(zhi)板系(xi)統(tong)(tong)(tong)現場uo信(xin)(xin)號(hao)經光電藕(ou)合(he)器(qi)隔(ge)離，與控(kong)制(zhi)板系(xi)統(tong)(tong)(tong)本體(ti)分開，切斷(duan)了(le)干(gan)擾(rao)噪聲(sheng)的通道，解決了(le)輸(shu)入(ru)、輸(shu)出回路(lu)的抗干(gan)擾(rao)問題，使系(xi)統(tong)(tong)(tong)調試方便(bian)，運行可(ke)靠。

結束語

工程實(shi)踐表明(ming)，采用以上杭干(gan)擾(rao)(rao)設(she)計和措施可以取得很好的(de)效(xiao)果。但是(shi)控制板系統中(zhong)的(de)干(gan)擾(rao)(rao)是(shi)一個十(shi)分復雜的(de)問題，還需(xu)在實(shi)踐中(zhong)不斷摸(mo)索，綜合考慮各(ge)方面的(de)因素(su)，進一步完善(shan)優化抗(kang)干(gan)擾(rao)(rao)設(she)計方法，合理有效(xiao)地抑制干(gan)擾(rao)(rao)。