Vojko Matko

Next Generation AT-Cut Quartz Crystal Sensing Devices

Generally, AT-cut quartz crystals have a limited scope of use when it comes to high-precision measurement of very small impedance changes due to their nonlinear frequency-temperature characteristics in the range between 0 °C and 50 °C. The new method improving quartz oscillator frequency-temperature characteristic compensation is switching between two impedance loads. By modifying the oscillator circuit with two logic switches and two impedance loads, the oscillator can switch oscillation between two resonance frequencies. The difference in resonance frequencies compensates the frequency-temperature characteristics influence as well as the influence of offset and quartz crystal ageing. The experimental results show that the new approach using the switching method highly improves second-to-second frequency stability from ±0.125 Hz to ±0.00001 Hz and minute-to-minute frequency stability from 0.1 Hz to 0.0001 Hz, which makes the high-precision measurement of aF and fH changes possible.

Quartz sensor for water absorption measurement in glass-fiber resins

The humidity sensor using the sensitive capacitive-dependent crystal is described. Presented is the probe sensitivity (dependence of df on the dCx). In addition, the new idea of excitation of the entire humidity sensor with stochastic test signals is described, and the humidity surface-measuring method is given. The latter includes the influence of test signals on the weighting function uncertainty. The results of the air-humidity measurement and water absorption measurement in glass-fiber resins are shown experimentally. The uncertainty of the surface humidity measurement is less than 0.1% (T=15-25 /spl deg/C and air-humidity=50 to 98%).

Measurement of 0-1 ml volumes using the procedure of capacitive-dependent crystals

In the paper, the use of a differential oscillator sensor structure in a capacitance sensor is presented. Investigations focused on the design and operation analysis of the oscillator differential structure in which the oscillation frequencies of the two oscillators are very close, and on the application analysis of capacitive-dependent crystals. In addition, the excitation of the entire sensor with stochastic test signals has been analyzed by the correlation deconvolution method which is also called the direct digital method (DDM). The compensation of temperature and voltage influences, as well as disturbing noise signals, are included. The area of operation and the uncertainty of the sensor with and without the test signal are given as well. When designing the capacitance sensor, the problems regarding the source of stable oscillation, compensation of temperature, the influence of supply voltage, noise, and A/D and D/A conversion occur in the operation range under 1pF. The pulse width module, which forms pulse-width modulated high-frequency current pulses, is the proposed solution. With these pulses, the capacitor in the integration element is charged or discharged. In this way, we benefit from the fact that the capacitors voltage increases linearly if it is charging by a constant current. As the charging is affected only by the current pulses which require an adequate current, the disturbing noise signals do not affect the capacitor charging. The correlation determination of the measuring value is primarily important for the determination of end values. Several experiments have been carried out to investigate the methods possible applications. The method is linear in the range of work and ensures the uncertainty in the range below 0.01%. The experimental results of 0-1 ml volume measurements are shown. The volume measurement uncertainty (0-1 ml) Is less than 0.05% (T=15 to 25/spl deg/C). >

Greatly Improved Small Inductance Measurement Using Quartz Crystal Parasitic Capacitance Compensation

Generally, quartz crystal inductance frequency pulling in oscillators is very low and therefore is not often used in practice. The new method of improving frequency pullability uses inductance to compensate for quartz stray capacitances. To this end, a special AT fundamental quartz crystal working near the antiresonance frequency is selected. By modifying its equivalent circuit with load inductance and series tuning capacitance, the magnetic sensing of the circuit can be highly improved. The experimental results show that the new approach using the quartz crystal stray capacitance compensation method increases the frequency pulling range (from ≅ 2 kHz/μH to ≅ 600 kHz/μH) by × 300 depending on the type of oscillator, making possible the measurement of nano-magnetic changes.

Major Improvements of Quartz Crystal Pulling Sensitivity and Linearity Using Series Reactance

This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of 3.5 to 21 MHz. The research describes high quartz pullability and linearity by varying the load capacitance. The paper also gives impedance circuits for crystal unit (3.5 MHz) together with load capacitance and compensation reactance. The experimental results show that the new approach using compensation method of quartz crystal connected in series reactance increases the frequency pulling range by ×25 to ×100 depending on the type of oscillator and compensation factor “k” in the temperature range of 10 to 40 °C.

Sensor for high-air-humidity measurement

Abstract A humidity sensor using a sensitive capacitance-dependent crystal is described. The probe sensitivity (dependence of d f on d C 1 ) is presented. In addition, the new idea of excitation of the entire humidity sensor with stochastic test signals is described, and the humidity surface-measuring method is given. It includes the influence of test signals on the weighting-function uncertainty and on the A/D-D/A conversion. The results of humidity measurement with the excitation signals are shown experimentally. The uncertainty of the surface humidity measurement is less than 0.2% ( T − 15–25°C and humidity = 50 to 98%).

New Quartz Oscillator Switching Method for Nano-Henry Range Inductance Measurements

This article introduces a new method for nano-Henry inductance measurements at the frequency of 4.999 MHz with a single quartz crystal oscillating in the switching oscillating circuit. The real novelty of this method, however, lies in a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 0 °C and 50 °C through a switching method which compensates for the crystal’s natural temperature characteristics. This allows for the compensation of any influences on the crystal such as the compensation of the non-linear temperature characteristics and the ageing of both the crystal and other oscillating circuit elements, as well as the reduction of the output frequency measurement errors with the help of an additional reference frequency. The experimental results show that the switching method greatly improves the measurement of small inductance changes in the range between μH and nH, allowing as a result high-precision measurements (∼0.35 fH) in this range.

On the use of quartz crystal capacitive dependence for measurement of 0–1 ml volumes

Abstract The use of a differential oscillator sensor structure in a capacitance sensor is presented. Investigations are focused on the design and operational analysis of an oscillator differential structure in which the oscillation frequencies of the two oscillators are very close, and on the application analysis of capacitive-dependent crystals. In addition, the excitation of the entire sensor with stochastic test signals has been analysed by the correlation deconvolution method, also known as the direct digital method (DDM). The compensation of temperature and voltage influences, as well as disturbing noise signals, is included. The area of operation and the uncertainty of the sensor with and without the test signal are given as well. When designing the capacitance sensor, the problems regarding the source of stable oscillation, temperature compensation, the influence of supply voltage, noise, and A/D and D/A conversion occur in the operation range under 1 pF. The pulse-width module, which forms pulse-width-modulated high-frequency current pulses, is the proposed solution. With these pulses the capacitor in the integration element is charged or discharged. In this way we benefit from the fact that the capacitors voltage increases linearly if it is charged by a constant current. As the charging is affected only by the current pulses, which require an adequate current, the disturbing noise signals do not affect the capacitor charging. Likewise, the pulse-width module compensates the effects of temperature and voltage by means of modulation. The correlation determination of the measuring value is of prime importance for the determination of end values. Two computer-aided modes of operation are suggested: dynamic measurement control and the correlation determination of differences. Several experiments have been carried out to investigate the methods possible applications. The experimental results of 0–1 ml volume measurements are shown. The method is linear in the range of work and ensures an uncertainty below 0.01% in this range. The volume-measurement uncertainty (0–1 ml) is less than 0.05% ( T = 15–25 °C).

High-Precision Hysteresis Sensing of the Quartz Crystal Inductance-to-Frequency Converter

A new method for the automated measurement of the hysteresis of the temperature-compensated inductance-to-frequency converter with a single quartz crystal is proposed. The new idea behind this method is a converter with two programmable analog switches enabling the automated measurement of the converter hysteresis, as well as the temperature compensation of the quartz crystal and any other circuit element. Also used is the programmable timing control device that allows the selection of different oscillating frequencies. In the proposed programmable method two different inductances connected in series to the quartz crystal are switched in a short time sequence, compensating the crystal’s natural temperature characteristics (in the temperature range between 0 and 50 °C). The procedure allows for the measurement of the converter hysteresis at various values of capacitance connected in parallel with the quartz crystal for the converter sensitivity setting at selected inductance. It, furthermore, enables the measurement of hysteresis at various values of inductance at selected parallel capacitance (sensitivity) connected to the quartz crystal. The article shows that the proposed hysteresis measurement of the converter, which converts the inductance in the range between 95 and 100 μH to a frequency in the range between 1 and 200 kHz, has only 7 × 10−13 frequency instability (during the temperature change between 0 and 50 °C) with a maximum 1 × 10−11 hysteresis frequency difference.

High Resolution Switching Mode Inductance-to-Frequency Converter with Temperature Compensation

This article proposes a novel method for the temperature-compensated inductance-to-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit to achieve better temperature stability of the converter. The novelty of this method lies in the switching-mode converter, the use of additionally connected impedances in parallel to the shunt capacitances of the quartz crystal, and two inductances in series to the quartz crystal. This brings a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 10 and 40 °C. The oscillator switching method and the switching impedances connected to the quartz crystal do not only compensate for the crystals natural temperature characteristics but also any other influences on the crystal such as ageing as well as from other oscillating circuit elements. In addition, the method also improves frequency sensitivity in inductance measurements. The experimental results show that through high temperature compensation improvement of the quartz crystal characteristics, this switching method theoretically enables a 2 pH resolution. It converts inductance to frequency in the range of 85–100 μH to 2–560 kHz.