When using the ellipse method in eddy current testing, what is the normal indication when the test specimen matches the reference standard?

In the context of using the ellipse method in eddy current testing, when the test specimen matches the reference standard, a straight horizontal line on a cathode ray tube is the normal indication observed. This indicates that the impedance of the test specimen is exactly the same as that of the reference standard.

The ellipse method typically involves mapping the signal response of the material being tested against a predetermined reference standard. When the test conditions perfectly align with the reference, the resulting display on the cathode ray tube would show a straight line rather than forming an ellipse or any other shape. This straight line confirms that the eddy current response of the specimen is consistent with the known characteristics of the standard, indicating no defects or variations have been detected.

Other potential indicators, such as an ellipse or null reading, signify different conditions or mismatches in the impedance values, while a clean base line on a strip chart might not provide as clear or direct a correlation as the straight line does, particularly in the context of the ellipse method.