Vector Extraction
Signal processing techniques resolve an alternating current waveform into two orthogonal components that represent its real and imaginary parts. Applying quadrature demodulation enables the simultaneous measurement of resistance and reactance in an inductive sensor. This method provides the complete vector information of the electrical signal.
Phase Separation
Reference signals with a ninety-degree phase difference are multiplied by the input waveform to generate the in-phase and quadrature outputs. These two channels are then low-pass filtered to remove the double-frequency products. The resulting voltages represent the coordinate values on the complex impedance plane.
Demodulator Circuitry
Analog multipliers or digital signal processors execute the multiplication of the input signal by the sine and cosine reference waves. The accuracy of the demodulation depends on the phase precision of the reference generator and the matching of the signal paths. Any imbalance between the in-phase and quadrature channels introduces a phase error that distorts the measurement vector.
Implementing this process in the digital domain eliminates the drift associated with analog component tolerances.
Offset Calibration
Residual voltages in the demodulator outputs must be measured and subtracted to ensure accurate impedance values at zero input. These offsets arise from amplifier bias currents and trace coupling within the instrument. Regular calibration against known reference impedances corrects these errors.
