Which adjustment can help in improving signal visibility during ultrasonic testing?

Signal visibility during ultrasonic testing is critical for accurately interpreting the test results. Gain adjustment plays a vital role in enhancing signal visibility because it directly affects the amplification of the received signals. By increasing the gain, even weak echoes from defects in the material or distant interfaces can be amplified, making them easier to detect on the display. This adjustment helps ensure that the signals of interest are distinguishable from background noise and other unwanted signals.

While other adjustments such as frequency adjustment or speed adjustment are important for optimizing the overall testing configuration or addressing specific material properties, they do not primarily focus on enhancing the visibility of the signals already being received. Temperature adjustment also does not directly influence signal visibility in terms of echo amplification. Therefore, gain adjustment is the most effective method among the options for improving signal visibility in ultrasonic testing.