西南医用设备厂生产的ＫＣ-400ｍＡＸ光机属于70年代产品,该设备计时器电路采用两个闸流管Ｇ1、Ｇ2控制,并通过ＲＣ电路的充放电过程来控制Ｘ线曝光时间。电路要求Ｇ1管在交流50周/秒某一固定相位点起辉点燃,使得摄影继电器ＳＣ接点闭合的瞬间恰好处于交流某半周的零点,同时要 The KC-400mAX light machine produced by Southwest Medical Equipment Factory belongs to the 70s product. The timer circuit of the device is controlled by two thyristors G1 and G2, and the X-ray exposure time is controlled by the charging and discharging process of the RC circuit. The circuit requires the G1 tube to ignite and fire at a certain fixed phase point of the AC 50 cycles/second, so that the moment when the photo-relay SC contact is closed happens to be at the zero point of a certain half-cycle of the AC.