Which device controls the amount of time kilovoltage potential (kVp) is applied to the x-ray tube?

The device that controls the amount of time kilovoltage potential (kVp) is applied to the x-ray tube is the exposure timer. The exposure timer is crucial in radiography as it determines the duration that the x-ray beam is generated. This timing is essential for producing images with the correct density and contrast.

When the exposure timer is activated, it enables the high voltage from the power source to be applied to the x-ray tube for a specified period. This allows for the precise control of radiation dose delivered to the patient and ensures the optimal exposure of the image receptor. This is particularly important for preventing overexposure or underexposure, which can significantly affect the quality of the radiographic image.

While other devices, like the autotransformer and step-up transformer, play roles in adjusting voltage levels, their functions do not involve regulating the duration of exposure. The kilovoltage peak (kVp) meter is used to measure the kilovoltage but does not control the timing of the exposure. Therefore, the exposure timer is the correct answer as it directly manages how long the high voltage is applied during the x-ray exposure process.