Highly Sensitive Dual Quartz Reactance-to-Frequency Transducer

A new high sensitivity temperature-compensated reactance- to-frequency transducer with two quartz crystals oscillating in the switching oscillating circuit is presented. The novelty of this method lies in the switching-mode converter bringing a considerable reduction of the temperature influence of AT-cut crystal (the crystal's x axis is inclined by 35°15' from the z (optic) axis) frequency change in the temperature range between 10−50 °C and in the use of additionally connected sensing reactance in parallel to the shunt capacitances of the two quartzes. The oscillator switching method and parallel switching reactances connected to the quartz crystals do not only compensate crystals' natural temperature characteristics but also any other influences on the crystals such as ageing of both the crystals and other oscillating circuit elements. In addition, the method also improves reactance-to-frequency sensitivity, linearity and reduces the output frequency measurement error. The experimental results show that through high temperature compensation improvement of the quartz crystals' characteristics, this switching method theoretically enables a 100 zF resolution. It converts capacitance in the range 4−8 pF to frequency in the range 2−100 kHz.