TIMERS. BASIC X-RAY SCHEMATIC. TIMER CIRCUIT:. IS SEPARATE FROM THE OTHER MAIN CIRCUITS OF THE IMAGING SYSTEM . . TIMER. TIMER. A MECHANICAL OR ELECTRONIC DEVICE WHOSE ACTION IS TO MAKE OR BRAKE THE HIGH VOLTAGE ACROSS THE X-RAY TUBE. TYPES OF TIMING CIRCUITS TIMERS:. MECHANICAL
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UNLESS TUBE POTENTIAL IS LESS THAN 50 kVp – 2,000 mAs IS THE LIMIT.
Automatic exposure control devices can assist the radiographer in producing consistent radiographic images from patient to patient, regardless of size or presence of pathology. The advantages of this consistency are numerous and include: decreased repeat rate; decreased patient exposure; and increased department efficiency. The most important benefit being decreased repeat rate
When an AEC device is used to terminate an exposure, the technologist sets the kVp and mA, but the time of the exposure is automatically determined by the machine. The AEC device differs from a manual timer because the AEC does not stop the exposure until the film has reached an appropriate density. Unlike manual timers, which simply stop the exposure after the preset time has elapsed.
A major benefit of the AEC device is its ability to consistently obtain accurately exposed radiographs, even in the presence of pathology. While manual timers terminate the exposure at the preset time, regardless of pathology or achievement of proper film density. The following example demonstrates the difference
Along with proper
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Even though the ionization chamber and the phototimer operate differently, they both have the same function: convert radiation into an electrical signal which will be used to automatically stop the exposure when the film has reached the proper density
Without a technologist who is very knowledgeable about anatomy and positioning, automatic timers are worthless. In fact, they may actually decrease department efficiency because of the increased amount of repeat radiographs that will result if used improperly.