Why does DR use the X-ray exposure hand switch with two exposures?

Do you know why dr needs X-ray exposure hand switch with two exposures? First, I will explain the X-ray exposure hand switch to everyone. According to its structure, analyze the working process of its different X-ray exposure hand switch. The X-ray exposure hand switch of the first gear only has a pair of normally open switches inside, which control the opening and closing of a circuit to control the high-voltage circuit of the X-ray machine. When the button gear is pressed, the gear will sink. Drive the contact to make the circuit closed, and the X-ray high-voltage circuit is energized to generate high voltage to generate X-rays. When the button position of the hand brake is released, the button position rises, so that the contact is disconnected and the circuit is disconnected. Because there is no high-voltage supply, X-rays are no longer generated. In the double-speed X-ray exposure hand switch, two pairs of normally open switches with different stroke control circuits are installed. The contacts of the normally open switch control the two circuits respectively. The X-ray exposure hand switch in the first gear controls the X-ray machine. The camera is ready for shooting, the preparation circuit is turned on, and the X-ray machine is in the pre-exposure state. This state can be cancelled. Release the button cap to cancel the start of the cancellation process without X-ray generation. The contact of the normally open switch controlled by the second gear button position controls the high-voltage generating circuit of the X-ray machine to close and generate X-rays. After releasing it, all the above-mentioned circuits are cut off and the machine returns to the unexposed state.
To put it simply, DR sets the X-ray exposure hand switch with two levels of exposure, the first level is the preparation work, the doctor and the patient are ready to enter the state of preparation, the second level of exposure is over.