What is it about?
This paper offers an explanation of the possible mechanism behind the CW-ACW differences. It was shown in reference [16] that H-coils do not have perfect immunity to off-axis components of magnetic field and detect some erroneous signals caused for example by the normal field (perpendicular to the sample surface). Theoretical analysis shows that such erroneous signals can responsible for the CW-ACW differences.
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Why is it important?
The CW-ACW differences are known to be significant at high rotational flux density (above 1.5T for electrical steels). This effect is well documented and explained on the basis of angular misalignment between the B and H sensors, as described in the references [13, 14]. However, there was no explanation of the CW-ACW differences which are still present at lower excitations (1.2 T and below). This paper explains that such effects can arise simply due to the off-axis sensitivity of the H-coils. The power loss averaged from CW and ACW measurements is not affected, because the errors cancel each other.
Perspectives
This paper presents a continuation of the research presented in references [13, 14]. These papers offer explanations of the multiple effects which need to be taken into account if the measurement uncertainties are to be reduced.
Stan Zurek
Megger Instruments Ltd
Read the Original
This page is a summary of: Effect of off-axis H-coil sensitivity on clockwise–anticlockwise differences of rotational power loss in isotropic samples , IET Science Measurement & Technology, February 2018, the Institution of Engineering and Technology (the IET),
DOI: 10.1049/iet-smt.2017.0385.
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