In setting up an ultrasonic inspection, the repetition frequency should be set to ensure the period is at least as long as the operating time.

• A. The same as the transducer resonance frequency
• B. So that its period is at least as long as the operating time
• C. As low as possible to avoid over-pulsing and distortion
• D. According to the instruction manual of the instrument

Answer: (B)

In pulsed ultrasonic testing, you must ensure the pulse repetition period allows the wave to travel to the farthest reflectors and back before the next pulse is emitted. If the period is shorter than this operating time, echoes from successive pulses will overlap, making the data hard to interpret. Hence the repetition frequency should be set so that the period is at least as long as the operating time, which means PRF must be low enough to satisfy this timing requirement. The other options don’t address this critical timing: the transducer’s resonance frequency is about the pulse shape, not how quickly you can repeat pulses; making the period as long as possible would waste inspection time without improving signal validity; and while manuals provide guidance, the core principle is matching the period to the maximum travel time to avoid overlap.