If the assigned exposure time is 72 ms, the actual exposure time must be accurate within which range?

If the assigned exposure time is 72 ms, the actual exposure time must be accurate within which range?

• A. +/- 0.72 ms
• B. +/- 1.44 ms
• C. +/- 3.6 ms
• D. +/- 7.2 ms

Answer: (C)

The key idea is how tightly the exposure timer must match the set time. In radiography QA, timer accuracy is typically checked as a percentage of the intended exposure, often ±5%. So for an exposure set at 72 milliseconds, 5% of 72 is 3.6 milliseconds. That means the actual exposure time should fall within 72 ms ± 3.6 ms, i.e., from 68.4 ms to 75.6 ms. The tolerance of ±3.6 ms is the correct one because it matches the standard ±5% allowance. The other values correspond to smaller or larger percentage tolerances (±1%, ±2%, ±10%), which don’t align with that usual standard.

The key idea is how tightly the exposure timer must match the set time. In radiography QA, timer accuracy is typically checked as a percentage of the intended exposure, often ±5%. So for an exposure set at 72 milliseconds, 5% of 72 is 3.6 milliseconds. That means the actual exposure time should fall within 72 ms ± 3.6 ms, i.e., from 68.4 ms to 75.6 ms. The tolerance of ±3.6 ms is the correct one because it matches the standard ±5% allowance. The other values correspond to smaller or larger percentage tolerances (±1%, ±2%, ±10%), which don’t align with that usual standard.