描述
DR-100-24
梯形图中的互锁和按钮联锁电路只能保证输出模块中与Y0和Y1对应的硬件继电器的常开触点心不会同时接通。由于切换过程中电感的延时作用,可能会出现一个接触器还未断弧,另一个却已合上的现象,从而造成瞬间短路故障。可以用正反转切换时的延时来解决这一问题,但是这一方案会增加编程的工作量,也不能解决不述的接触器触点故障引起的电源短路事故。(http://www.diangon.com/版权所有)如果因主电路电流过大或接触器质量不好,某一接触器的主触点被断电时产生的电弧熔焊而被粘结,其线圈断电后主触点仍然是接通的,这时如果另一接触器的线图通电,仍将造成三相电源短路事故。为了防止出现这种情况,应在PLC外部设置由KM1和KM2的辅助常闭触点组成的硬件互锁电路(见图2),假设KM1的主触点被电弧熔焊,这时它与KM2线圈串联的辅助常闭触点处于断开状态,因此KM2的线圈不可能得电。
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