描述
DR-100-24
梯形圖中的互鎖和按鈕聯(lián)鎖電路只能保證輸出模塊中與Y0和Y1對應的硬件繼電器的常開觸點心不會同時接通。由于切換過程中電感的延時作用,可能會出現(xiàn)一個接觸器還未斷弧,另一個卻已合上的現(xiàn)象,從而造成瞬間短路故障??梢杂谜崔D(zhuǎn)切換時的延時來解決這一問題,但是這一方案會增加編程的工作量,也不能解決不述的接觸器觸點故障引起的電源短路事故。(http://www.diangon.com/版權(quán)所有)如果因主電路電流過大或接觸器質(zhì)量不好,某一接觸器的主觸點被斷電時產(chǎn)生的電弧熔焊而被粘結(jié),其線圈斷電后主觸點仍然是接通的,這時如果另一接觸器的線圖通電,仍將造成三相電源短路事故。為了防止出現(xiàn)這種情況,應在PLC外部設(shè)置由KM1和KM2的輔助常閉觸點組成的硬件互鎖電路(見圖2),假設(shè)KM1的主觸點被電弧熔焊,這時它與KM2線圈串聯(lián)的輔助常閉觸點處于斷開狀態(tài),因此KM2的線圈不可能得電。
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