PHASE DETECTOR AND A/D CONVERTER
Phase and absolute value of the unknown impedance is obtained by multiplying the unknown AC voltage with a
square wave that is coherent with the stimulus. The mean value of the multiplier output is proportional to the inphase
or quadrature component of the unknown voltage. A total of four such measurements, in which the phase
of the square wave is advanced by 90°, resolves the unknown voltage into orthogonal components. This process
is applied for both the voltage and the current. Therefore, eight measurements are needed for the final
calculation. Anti-phase components are substrated (0° with 180° and 90° with 270°), consequently eliminating
all common offsets and reducing noise. Each of these voltages measurements is meaningless by itself, because
the reference square waves signals have no particular phase relationship to the measured analog signals, and
because the current through Zx is not controlled.
The AC signal voltage from the phase-sensitive detector is integrated, during an integer test signal period that is
near 20ms (50Hz operation) or 16.67ms (60Hz operation), together with a DC offset. This ensures that the final
result is always the same sign. The value of the voltage is obtained by timing the discharge of the capacitor with
a 17-bit counter inside the controller.
TRANSFORMER PARAMETER MEASUREMENT
This function measures transformer parameters through an IC switch, permitting the measurement of the High
Sense voltage for the secondary side or High Drive for the primary side of the transformer. The Low Drive and
Low Source terminals are connected to ground through a virtual ground. In Mutual Inductance measurement
mode, the instrument measures the primary current and the secondary voltage to compute the mutual inductance