Why IWATSU’s Cross-Power Method Matters When Selecting a B-H Analyzer
For engineering teams evaluating a suitable B-H analyzer, the central question is often whether the system can generate reference quality magnetic data: core loss, amplitude permeability, and related characteristics measured with sufficient rigor to support material selection, design validation, supplier comparison, and customer-facing engineering claims.
That is the practical context behind IWATSU’s statement: “Cross-Power method (Compatible to IEC 62044-3 standard)”. It refers to a specific loss-measurement architecture within the IEC 62044-3 framework, and that architecture becomes highly relevant when measurement accuracy is limited not by the specimen itself, but by the amplitude and phase behavior of the measurement chain.
What IEC 62044-3 Means in Practice
IEC 62044-3 defines measuring methods for power loss and amplitude permeability of soft-magnetic cores forming closed magnetic circuits, intended for high-excitation operation in inductors, chokes, transformers, and similar power-electronics applications. Importantly, the standard does not reduce core-loss measurement to one universal method. Instead, it includes several recognized multiplying methods, including the V-A-W meter method, impedance analyzer method, digitizing method, vector spectrum method, and cross-power method.
The cross-power method is a named method within the standards structure used for high-excitation magnetic measurements. Its real significance is that it addresses one of the hardest technical issues in electrical core-loss measurement: phase-related measurement error.
How the Cross-Power Method Compares to Other Measurement 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 waveforms | Data acquisition domain | Data processing domain |
|---|---|---|---|
| V-A-W meter | Sinusoidal waveforms | Time | Time |
| Impedance analyzer | Sinusoidal waveforms | N/A | N/A |
| Digitizing | Arbitrary | Time | Time |
| Vector spectrum method | Arbitrary | Frequency | Frequency |
| Cross-power method | Arbitrary | Time | Frequency |
This comparison [IEC 62044-3] highlights the defining characteristic of the cross-power method: it acquires the measured signals in the time domain and performs the loss-related evaluation in the frequency domain. For measurements in which phase shift and frequency-dependent transfer behavior are significant contributors to uncertainty, that distinction is technically important.
A digitizing approach remains a time-acquisition / time-processing method. The cross-power method retains the practical advantages of time-domain sampling while moving the power evaluation into the domain in which spectral magnitude and phase can be resolved explicitly for the fundamental and harmonic components.
The Measurement Problem the Analyzer Must Solve
In a winding-based B-H analyzer arrangement, the system measures excitation current in the primary path and induced voltage in the secondary path. From those signals, it derives field strength, flux density, and ultimately core-loss density. In simplified form:
These relations are standard. The measurement challenge lies in the fact that the analyzer does not observe idealized quantities directly. It measures signals that pass through a current shunt, sensing circuitry, amplifier stages, cables, A/D converters, and digital processing.
Why Phase Correction Matters So Much
In many AC magnetic measurements, especially at higher frequency, the voltage-related and current-related terms can approach a 90° phase relationship. Under those conditions, the real-loss term becomes a relatively small component extracted from much larger reactive energy flow. That makes the loss calculation highly sensitive to phase discrepancy.
If the measurement chain introduces phase shift that is not properly corrected, the resulting loss value may be repeatable and still deviate enough to affect material ranking, thermal modeling, and design tradeoffs.
These plots show the practical consequence of phase correction in core-loss measurement. In the example presented, the measured core-loss value differs by approximately 20% between the Digitizer method and the Cross-Power method at around 500 kHz. The slide attributes this difference to the fact that, in the Digitizer method, the frequency-dependent behavior between the current-detection resistor and the respective detection circuits 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 cycles of the measured voltage waveforms and converting them into digital data. Both methods therefore start from sampled time-domain information.
In the Digitizer method, the subsequent loss-related processing is carried out directly on the sampled time-axis waveforms. This is a recognized approach within the IEC multiplying-method framework. However, it remains a time-domain processing method. Frequency-dependent amplitude and phase behavior in the current-sensing path and associated detection circuitry are not resolved in a harmonic-by-harmonic spectral calculation.
What the Cross-Power Method Does Differently
The Cross-Power method is suitable for arbitrary excitation waveforms. For a specified excitation level, one or more cycles of the measured voltage signals are acquired and converted into digital data. The complex spectrum of those measured cycles is then calculated by FFT.
From these spectral data, the analyzer determines the cross-power spectrum. The core-loss power is obtained by summing the real parts of that cross-power spectrum across frequency. In practical terms, the method resolves the relevant spectral components of the measured signals, including the fundamental and harmonic terms, together with their phase relationships, and evaluates their real-power contributions frequency by frequency.
In this expression, Uak and Ubk are the RMS values of the two measured voltage signals at harmonic order k, φk is the phase angle between them, and α is a proportionality constant determined by the measurement-circuit configuration.
This formulation is useful because it expresses the Cross-Power method as a harmonic-domain real-power calculation. The analyzer does not rely only on the raw sampled waveforms. It decomposes them spectrally, evaluates the contribution of each frequency component, and sums the real-power terms across the spectrum to determine the measured core-loss power.
The measurement-principle drawing is consistent with this signal-processing sequence. It shows the excitation source and power amplifier, the compensated source path, the current shunt used to derive the excitation-current signal, the voltage measured across the excitation winding, and the induced voltage measured in the secondary winding. These measured channels are digitized and then routed into the FFT / IFFT processing stage, where spectral evaluation and correction are carried out.
For a technical reader, the relevance of the drawing is that it places the Cross-Power method in the complete measurement chain. The method includes stimulus, sensing, digitization, spectral evaluation, correction, and waveform reconstruction.
Why This Matters in a Purchase Decision
For teams selecting a B-H analyzer, Cross-Power is relevant because it reduces uncertainty associated with frequency-dependent behavior in the sensing and detection paths. In high-frequency magnetic measurements, and particularly with low-loss or high-Q materials, the real-loss term can be sensitive to phase discrepancy between measured quantities. A method that evaluates power spectrally and sums the real contributions across frequency provides a more rigorous basis for loss determination under those conditions.
This is particularly relevant in three situations:
- High-frequency characterization, where parasitics and phase effects become increasingly significant.
- Low-loss or high-Q materials, where relatively small measurement error can materially affect the reported loss value.
- Programs requiring waveform flexibility, where applicability to arbitrary excitation waveforms is important.
Conclusion
For organizations evaluating a B-H analyzer, IWATSU’s Cross-Power method is best understood as a frequency-domain loss-evaluation architecture within the IEC 62044-3 multiplying-method framework. It acquires the measured signals in the time domain, calculates their complex spectra by FFT, derives the cross-power spectrum, and determines core-loss power by summing the real spectral contributions across frequency. That architecture is well suited to applications in which phase accuracy and frequency-dependent transfer behavior are significant contributors to measurement uncertainty.
