DJB Instruments

You are here: Products Instrumentation Converters QV/01

Instrumentation - QV/01

E-mail Print PDF

Minature 2 Wire Charge/Voltage Converter • Low Impedance Line Driver Maintains Data Integritity Over Distances up to Several Hundred Meters • 1 & 10mV/pC Gain Options • L.F. Option

Comparison QI/01 VS. QV/01

Transmission path induced noise may significantly degrade data derived from piezoelectric transducer sources ; solutions based on signal amplifications prior to transmission are the QI/01 charge/current converter and the QV/01 charge/voltage converter outlined here.
Both are energised from a power source situated at the outlet end of signal line, and signal is superimposed on energisation for the minimal two wire interconnection.

Optimally, the QI/01 must interface to a current sink, and this gives a line drive capability considerably in excess of that of the voltage drive QV/01 by virtue of its zero voltage transmission environment.

The voltage drive inherently acts as energy source for the line reactive load and there is thus an implied constraint on line length - however, interface requirements are minimal.

QV/01 Drive Capability

The QV/01 power source provides a constant current.

That in excess of the minimal quiescent requirement of the QV/01 represents line drive capability, translatable in terms of line length.

Thus for a 4mA power source and a 5Vpk.,

5kHz maximum drive requirement, the 2½ mA pk. excess will drive a 2kΩ reactive load, equivalent to some 160metres of 100pF/M coaxial cable.

Power source current may be increased to 20mA in circumstances demanding enhanced capability, deducting 1½ mA gives line drive current. Because the QV/01 is inherently constrained to fairly short length line drive applications, line filtering and voltage drop limitations are insignificant.

Interfacing

The minimal interface comprises a voltage supply and series current diode (Fig.1.).

Signal is extracted at the diode/line junction. Supply ripple rejection is of the order 70dB therefore there is no mandatory requirement for high order supply regulation. QV/01 bias voltage is around 9V @ 20°C, increasing to 11/12V @ 125°C.
Clearly this has implications in terms of supply voltage, 18V being the minimum allowable without signal amplitude constraint at maximum operating temperature.

Transducer voltage supplies incorporated into spectrum analysers, data recorders etc... should be evaluated for correct energisation, voltages as low as 12V, will severely curtail QV/01 output.

VV/04 incorporates 28V, 4mA transducer supply, transducer O/C & S/C indication, 1/110mV/g normalising range, 6 x 10dB increment O/P signal scalings from 0.0316 to 10g/volt and provides complete interfacing for both QV/01 and for transducers with integral charge/voltage converters.

Construction

Thick film hybrid charge/voltage converter housed in 15 x 15 x 10mm, hard anodised aluminium block (QV/01).

Thick film hybrid charge/voltage converter housed in an inline joiner for BNC (TNC) socket & Microdot plug (QV/02).

Instrumentation-QV-01