说明：  电气控制与plc实训教程电子教案的第九部分B，对学习的人很有帮助，讲解细致，思路清晰，我觉得相当不错，与大家一起分享！
(Electrical control and plc Training Tutorial Part IX of electronic teaching plan B, to learn helpful to explain the meticulous, clear-headed, I feel pretty good to share with everyone!)