A term used to define an instrumentation technique that discriminates between variables by phase angle changes is:

The correct answer is related to the method that involves evaluating the phase angle of signals to differentiate between various variables in Eddy Current Testing. Phase analysis involves examining the shifts in phase angle that occur in the eddy currents when interacting with different materials or flaws. By analyzing these phase shifts, the testing equipment can provide valuable insights into the properties of the material being inspected, including identifying changes in conductivity or permeability that may indicate flaws or inconsistencies.

This technique is crucial in Eddy Current Testing because it allows for a more nuanced understanding of the material's condition than simply measuring amplitude. By focusing on phase changes, inspectors can more accurately determine the nature and extent of any defects present, leading to better assessments of structural integrity and reliability.

In contrast, the other terms do not effectively describe the specific technique used in this context. Phase distortion may refer to the alteration of a signal's phase due to various external influences, but it does not directly address the discrimination between variables. Phase shifting generally refers to the deliberate alteration of a signal's phase without the analytical framework of determining differences in material properties. Meanwhile, phase discrimination suggests a broader concept and lacks the specific emphasis on analyzing phase relationships inherent to phase analysis. Thus, it is the detailed process of phase analysis that encapsulates the