When an EXPOSE signal is received to begain x-ray,backup contactors(K1 through K4)are turned on and power is applied to the bucky,if a bucky has been selected.

• 当接到开始X线放射的曝光信号的时候，K1到K4四个备用接触器就会闭合，这样，如果预选了滤线器的话，电源就会加在滤线器上。