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For engineering teams evaluating a suitable B-H analyzer, the central question is usually whether the system can produce reference-grade magnetic data—core loss, amplitude permeability, and related characteristics—measured rigorously enough to support material selection, design verification, supplier comparisons, and customer-facing engineering claims.
That is the practical context behind Iwatsu's claim of a "cross-power method (compliant with IEC 62044-3)." It refers to a specific loss-measurement architecture within the IEC 62044-3 framework—one that becomes critical when measurement accuracy is limited by the amplitude and phase behavior of the measurement chain rather than by the sample itself.
What IEC 62044-3 Means in Practice
IEC 62044-3 defines methods for measuring power loss and amplitude permeability of soft magnetic cores forming a closed magnetic circuit, under high-excitation conditions in inductors, chokes, transformers, and similar power-electronics applications.
Importantly, the standard does not reduce core-loss measurement to a single generic method. Instead, it covers several recognized multiplying methods, including the V-A-W meter method, the impedance-analyzer method, the digitizer method, the vector-spectrum method, and the cross-power method.
The cross-power method is one of the named approaches in the standard's structure for high-excitation measurements. Its real significance lies in solving one of the hardest technical problems in electrical core-loss measurement: phase-dependent measurement error.
In demanding magnetic measurements, the challenge is often not waveform capture. It is ensuring that the reported core loss reflects the magnetic sample itself rather than the transfer characteristics of the measurement chain.
How the Cross-Power Method Compares to Other Approaches
One of the clearest ways to understand the value of the cross-power method is to compare it with the other multiplying methods classified in the IEC framework.
| Measurement Method | Applicable Excitation Waveform | Data Acquisition Domain | Data Processing Domain |
|---|---|---|---|
| V-A-W meter | Sinusoidal | Time | Time |
| Impedance analyzer | Sinusoidal | None | None |
| Digitizer | Arbitrary | Time | Time |
| Vector spectrum method | Arbitrary | Frequency | Frequency |
| Cross-power method | Arbitrary | Time | Frequency |
This comparison, described in IEC 62044-3, highlights the defining characteristic of the cross-power method: it acquires measurement signals in the time domain and performs the loss-related evaluation in the frequency domain. This distinction matters technically for measurements where phase offset and frequency-dependent transfer behavior contribute significantly to uncertainty.
The digitizer method remains a time-acquisition and time-processing approach. The cross-power method retains the practical advantages of time-domain sampling while moving power evaluation into a domain where the spectral amplitude and phase of the fundamental and harmonic components can be resolved explicitly.
The Measurement Problem the Analyzer Must Solve
In a winding-based B-H analyzer, the system measures the excitation current in the primary path and the induced voltage in the secondary path. From these signals it derives field strength, flux density, and ultimately core-loss density. In brief:
Why Phase Correction Matters So Much
In many AC magnetic measurements, especially at high frequency, the voltage-related and current-related terms can approach a 90-degree phase relationship. Under these conditions, the real loss term becomes a relatively small component extracted from a much larger reactive flow. This makes the loss calculation extremely sensitive to phase differences.
If phase offsets introduced by the measurement chain are not properly corrected, the resulting loss values may be repeatable yet still large enough to affect material rankings, thermal models, and design trade-offs.
These plots show the practical impact of phase correction in core-loss measurement. In the example presented by Ryu Nagahama at PSMA 2018, the measured core-loss values differ by roughly 20% between the digitizer method and the cross-power method at around 500 kHz.
The slide attributes this discrepancy to frequency-dependent behavior between the current-sense resistor and the corresponding sensing circuit in the digitizer method that is not compensated on the frequency axis. For engineering evaluation, that level of deviation is significant.
What the Digitizer Method Does
Both the digitizer method and the cross-power method begin by acquiring one or more periods of the measured voltage waveforms and converting them to digital data. Both methods therefore start from sampled time-domain information.
In the digitizer method, the subsequent loss-related processing is performed directly on the sampled time-axis waveforms. This is a recognized method within the IEC multiplying framework. However, it remains a time-domain processing approach. Frequency-dependent amplitude and phase behavior in the current-sensing path and associated detection circuitry cannot be resolved through harmonic-by-harmonic spectral computation.
What the Cross-Power Method Does Differently
The cross-power method works with arbitrary excitation waveforms. For a given excitation level, one or more periods of the measured voltage signals are collected and converted to digital data. The complex spectra of these measurement periods are then computed via FFT.
From these spectral data, the analyzer determines the cross-power spectrum. Core-loss power is obtained by summing the real part of the cross-spectrum. In practice, the method resolves the relevant spectral components of the measured signals—including the fundamental and harmonic terms and their phase relationships—and evaluates their real-power contributions frequency by frequency.
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