麵mian對dui限xian位wei開kai關guan，左zuo邊bian的de兩liang個ge接jie線xian點dian接jie控kong製zhi電dian機ji下xia降jiang的de接jie觸chu器qi下xia端duan，右you邊bian兩liang個ge接jie線xian點dian接jie控kong製zhi電dian機ji上shang升sheng的de接jie觸chu器qi下xia端duan。兩liang個ge接jie觸chu器qi同tong一yi相xiang序xu的de公gong共gong線xian接jie限xian位wei開kai關guan中zhong間jian三san個ge接jie線xian點dian中zhong間jian的de那na個ge，電dian機ji線xian接jie到dao中zhong間jian三san個ge接jie線xian點dian。