VV/04 interface for QVC two wire charge/voltage converters includes QVC power supply and open/short circuit indicators, normalising and range amplifiers. QVCs convert an input charge to a low impedance voltage superimposed upon the supply line.
Thus a coaxial lead suffices for routing power and signal between QVC and interface instrumentation.

Energisation is from a current source (voltage source with series resistor or constant current diode).
QVCs are immune to supply voltage noise but have limited line drive capability as connecting lead capacitance presents a reactive load.

Where signal level is adequate, the minimal interface shown in Fig.1 may suffice. However, the VV/04 adds gain, calibration and monitoring enhancements to the measurement system, improving dynamic range and ease of use.

VV/04 schematic is shown in Fig.2.
The input terminal connects internally to the current source and the normalising amplifier section, and is the monitoring point for the QVC open/short circuit indicator LEDS.

The normalising section provides an output of 100mV/g (O/P1) for transducer/QVC sensitivities within the range 1/110mV/g by means of a three decade digi-switch and x1/x10 multiplier switch directly set to transducer sensitivity.

In addition the range amplifier provides outputs of 1V/0.0316, 0.1, 0.316, 1, 3.16 or 10g (O/P2), selectable by 6 position switch.
For transducer sensitivities outside the direct dialled normalising range, or to shift the dynamic range, a normalising scaling factor may be used.