The autotransformer includes which of the following devices?

The autotransformer is a key component in radiographic imaging systems that is responsible for adjusting the voltage sent to the step-up transformer. It operates on the principle of self-induction, allowing for the precise control of kilovoltage. The kilovoltage peak (kVp) selector is integrated within the autotransformer to allow the radiologic technologist to choose the desired kVp for the exposure. By adjusting the tap that receives the voltage, the kVp selector enables the adjustment of the voltage supplied to the x-ray tube, directly influencing the quality and penetrating power of the x-rays produced.

The other devices listed serve different functions in the x-ray machine. For example, a kVp meter measures the actual kilovoltage being delivered, but it does not adjust the voltage itself. A circuit breaker is a safety feature that protects the electrical circuit from overloads but is not directly involved in the voltage regulation process. An exposure timer controls the duration of the exposure but does not have a role in setting the kilovoltage. Thus, the focus of the autotransformer as a voltage-adjusting mechanism clearly highlights why the kVp selector is the correct choice among the options provided.