AN2: Accuracy of Contextual Instruments Impedance Measurement Systems
CI Impedance EIS
Precision you'd expect from a benchtop instrument, in a portable form factor
CI Impedance EIS was benchmarked directly against the Zurich Instruments MFIA, one of the highest-precision impedance analyzers on the market (1 mΩ to 1 TΩ, 1 mHz to 5 MHz). Across a wide impedance range and the full operating frequency band, CI Impedance EIS tracks the MFIA closely, on both resistance and reactance, in both 2- and 4-electrode configurations.
This validation was carried out in partnership with INSA Lyon's INL laboratory, using calibrated electrical circuit models representative of real tissue and electrode-contact behavior, giving results that translate directly to real measurement conditions rather than idealized test benches.
What the data shows
4-electrode measurements (right-leg and whole-body tissue models, with realistic skin-contact impedance):
- Absolute error under 2 Ω on resistance and 3 Ω on reactance, across the full 2 kHz-200 kHz range
- Performance in line with the MFIA reference across both physiological models tested
2-electrode measurements, across four circuit models spanning 4 Ω to nearly 1 MΩ:
| Impedance range | Resistance accuracy | Reactance accuracy |
|---|---|---|
| Mid-range (Model 2, ~10 kΩ) | Near-perfect match to reference | Near-perfect match to reference |
| High impedance (Models 3-4, 100 kΩ-1 MΩ) | Within 0-4%, in line with the MFIA | Within -2% to 2%, in line with the MFIA |
| Low impedance (Model 1, <100 Ω) | Comparable order of magnitude to the MFIA; relative error grows as expected at very low Ω, where even small absolute deviations read as large percentages | Same effect on reactance |
Fitting the acquired spectra to a circuit model (the standard workflow in bioimpedance analysis) further sharpens results: errors on the extracted circuit parameters (Rs, Rp, Cp) stay within a few percent across every model tested, matching the reference instrument's own fitting accuracy.
In vivo-representative models (leg and whole-body): CI Impedance EIS matches the MFIA closely, with sub-1% differences on the key fitted parameters.
Validated operating envelope
- Impedance: 4 Ω to 1 MΩ (2-electrode), validated against a reference-grade instrument
- Frequency: 200 Hz to 200 kHz
- Configurations: 2- and 4-electrode
Getting the most out of that accuracy
The results above reflect a controlled, well-characterized measurement setup. Real-world accuracy also depends on cabling and electrode choices specific to each application. See our companion note, Impedance Measurement Accuracy and Influencing Factors, for guidance on cable capacitance, electrode contact impedance, and how to extend accuracy further with shielded cabling.
Source: P. Lebas, B. Massot, A. Montalibet, A. Claude, L. Sevrin, C. Gehin, "BioZ: A Portable Multi-Frequency Bioimpedance Sensor," 2025 47th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2025. DOI: 10.1109/EMBC58623.2025.11252869