SECTION 3
CIRCUIT DESCRIPTIONS
3.1 GENERAL DESCRIPTION
When measuring Cp or Gp, a voltage is applied across the unknown and range resistor in
Figure 3-1. The voltage across the unknown is held constant to within one part in several
thousand by the 1kHz oscillator feedback control circuit. A current proportional to the value
of the unknown impedance is produced through the range resistor. The resultant voltage drop
across the range resistor is separated into two vector components by the Phase Sensitive
Detectors (PSD) and Reference Voltage Generator (RVG). Receiving gating signals from RVG, the
PSD will measure Gp, the component in phase (0°) with RVG, and Cp, the component at
quadrature (90°). The selected detector output is then fed to the A/D Converter which has a
readout of 1000 counts/volt.
When measuring Ls or Rs, a voltage is applied across the unknown and range resistor in Figure 3-1.
the voltage across the range resistor is held constant to within one part in several thousand by
the 1kHz oscillator feedback control circuit. With a constant current flowing through the
unknown, a voltage proportional to the value of the unknown impedance is developed across the
unknown. The resultant voltage drop is separated into two vector components by the Phase Sensitive
Detector (PSD) and Reference Voltage Generator (RVG). Receiving gating signals from the RVG, the PSD
will measure Rs, the component in phase (0°) with the RVG, and Ls, the component at quadrature (90°).
The selected detector output is then fed to the A/D Converter which has a readout of 1000 counts/volt.
3-1
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