Describe how thickness measurement is performed using PAUT.

Thickness measurement using Phased Array Ultrasonic Testing (PAUT) involves utilizing the time-of-flight principle, which is a fundamental aspect of ultrasonic testing. In this method, an ultrasonic pulse is generated and sent into the material. As the pulse travels through the material, it encounters interfaces, such as the back wall of the object being tested.

The time it takes for the pulse to travel through the material and back is measured, and knowing the speed of sound in the specific material, the thickness can be calculated. This direct correlation between the time-of-flight and thickness allows for accurate measurements to be taken.

The other options do not relate to the principles of PAUT in measuring thickness. A pressure gauge measures surface pressure or force rather than material thickness, visual inspection relies on human observation without the precision offered by ultrasonic methods, and calculating the density does not provide a direct measurement of thickness. Therefore, the reliance on the time-of-flight measurement in PAUT is crucial for obtaining accurate thickness readings.