Which circuit generates a burst of energy which is applied to the sending crystal?

The pulser is responsible for generating a burst of energy that is applied to the sending crystal in ultrasonic testing systems. This component creates a high-voltage electrical signal that excites the piezoelectric crystal, causing it to vibrate and emit ultrasonic waves into the test material. This process is crucial for the initiation of the testing cycle, as the emitted sound waves are what enable the detection of anomalies or features within the material being examined.

The other circuit options provided serve different functions. The receiver-amplifier is tasked with receiving the echoes of the ultrasonic waves that bounce back after interacting with the material, amplifying these signals for further analysis. The clock circuit regulates timing for various sequential operations within the system but does not generate the energy burst itself. Lastly, the signal conditioning circuit is involved in processing the received signals to improve their quality and prepare them for display or further analysis, but it does not play a role in the initial generation of the ultrasonic pulse. Thus, the pulser is the key component that initiates the ultrasonic testing process by generating the burst of energy needed to drive the sending crystal.