When using the linear time base method, what is applied to the vertical deflection plates of a cathode ray tube when the test specimen and reference standard are the same?

In the context of the linear time base method employed in Eddy Current Testing, when the test specimen and reference standard are identical, there is a specific condition that affects the output on the cathode ray tube (CRT). In this scenario, the vertical deflection plates of the CRT receive zero net voltage.

This occurs because both the test and reference signals are effectively the same when compared. Since these signals are identically matched in terms of their electrical properties (indicating there are no faults or differences in the material), the resulting net effect on the vertical deflection is null. Thus, the CRT displays a stable line without any vertical movement, signifying that there are no detected defects or variations that would cause a deviation from the reference standard. This principle is fundamental in ensuring accurate interpretations during the inspection process, as it allows operators to confirm the integrity of the material being tested.

In this scenario, the other options involve various waveforms that would introduce deflection on the CRT, indicating some level of difference between signals. However, in the case of identical test and reference specimens, they contribute nothing to the vertical deflection, affirming that zero net voltage is the correct interpretation.