A quartz resonator converts non-electric quantities into electrical ones. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

 Comments on the article

The quartz resonator is used not only for frequency stabilization and filtering of RF signals. Being a high-quality electromechanical oscillatory system, it is suitable for measuring non-electrical parameters in the technological control of products, semi-finished products and in environmental monitoring.

The quartz dissipative converter of mechanical energy is made on the basis of a specialized quartz resonator, in which the piezoelectric element is coated with a substance sensitive to the measured non-electric quantity. The output electrical signal of the transducer is fed to a measuring device or a computer. The objects of control can be gaseous, liquid and solid media, including liquid crystals and biopolymers, and the measured non-electrical quantities can be humidity, temperature, electrical, thermal and light conductivity, viscoelastic properties, etc.

When the converter is exposed to a measured non-electric quantity, the equivalent active resistance of the quartz resonator changes, which is a measure of the dissipation (scattering) of elastic oscillations of quartz. It is known that the resonator is an electromechanical oscillatory system containing a piezoelectric element, its electrodes with leads and a holder. The piezoelectric element is cut from a natural or synthetic quartz crystal. Electromechanical oscillations in the resonator occur due to the forward and reverse piezoelectric effects inherent in quartz.

In the main application of the resonator (stabilization and filtering of signals), its equivalent electrical (active) resistance Ra is called dynamic and is considered as a whole [1]. In fact, it can be divided into components: R0 is the resistance due to the loss of vibration energy in the quartz itself; Re - in the electrodes; R and - losses due to ultrasonic radiation; Rc - for coupled oscillations; Ra - losses in the holder.

When using a quartz resonator in an energy converter, it was necessary to obtain formulas for calculating all components of the resistance Ra, including Rp, which reflects additional losses in the sensitive coating - it is applied to the surface of the piezoelectric element to provide an informative output signal proportional to the value of the controlled non-electrical parameter [2]. Along with this, the converter must have a constant active resistance when changing non-informative parameters. To achieve independence of Ra from temperature, for example, losses due to coupled oscillations in the resonator should be excluded, which is achieved by changing the design of the electrodes on the piezoelectric element [3].

The calculation of the components according to the formulas in [2] made it possible to choose the type of cut of the piezoelectric element and determine its optimal dimensions. DT cut (yxl/-52 deg) with piezoelement dimensions 14,5x6,1x0,25 mm turned out to be optimal for a quartz dissipative converter of mechanical energy; resonant frequency - 300 kHz, Ra = 236 Ohm (without sensitive coating).

The value of the informative signal of the transducer (change in active resistance) is determined by the formula

where Kpr - conversion factor equal to 5416,74 kΩ/kg; Δ and μ are the thickness of the sensitive coating and its viscosity (internal friction).

Using as a sensitive coating a film of nylon (polyca-proamide), the internal friction of which depends on air humidity, it was possible to create a humidity converter-sensor, which became the basis of the moisture meter [4]. The dynamic resistance of the transducer in dry air (at a relative humidity of 20...30%) is 1,2 kOhm, and in humid (90...95%) - 3,265 kOhm, which corresponds to a sensitivity of at least 26 Ohm/%. The moisture meter has found application in the greenhouse farm of the Teplichny state farm (Ivanovo), as well as in the waveguides of the Ivanovo city and regional television stations. Note that in winter the temperature in the waveguide can drop to -35...45, and in summer it can reach +45 °C.

Interestingly, in the well-known VOLNA air moisture meters, a quartz resonator with a nylon moisture-sensitive film is also used as a sensor, but it uses the dependence of the resonant frequency of quartz on the mass of the sensitive coating. It is difficult to make such a device small-sized (pocket), since it must contain two quartz resonators and two self-oscillators.

The mechanism of energy dissipation of elastic vibrations of a piezoelement in a resonator is much more complicated, it is associated with relaxation processes in a sensitive polymer coating and the depth of penetration of an elastic wave into it. To obtain optimal moisture sensitivity, the polymer film applied to the piezoelectric element must have a certain ratio between its viscosity and elasticity, which is achieved by adding rigid phenol-polyvinyl acetate adhesive (BF-2) to the viscous nylon.

Note that some polymers, which have a significant mass increment in a humid environment, have a small dependence of internal friction on humidity and, therefore, are unsuitable for a humidity sensor due to its low sensitivity.

The design of the transducer used as an air humidity sensor is shown schematically in fig. 1]. On the piezoquartz plate 5 of the DT-cut with a natural oscillation frequency of 1 kHz, a conductive coating 300 is applied, to which current leads 2 are soldered. The places of maximum displacements B and deformation C are marked on the piezoelectric element. ethyl alcohol. The moisture-sensitive film 3 on the surface of the plate consists of layers of polymers with different moisture sensitivity and viscoelasticity.

Layering technology is simple. After applying the adhesive strips, the plate is dried at a temperature of 150 °C for 60 ± 10 min to polymerize the adhesive. Then it is dipped into a 30% solution of glue in ethyl alcohol and centrifuged in air with a rotation frequency of 2000 ... 2500 min "1 around the axis of the leads for 30 ... 40 s. On this thin film of glue, dried in air, a layer of nylon is applied from a 150% solution in formic acid.The films are dried again at a temperature of XNUMX ° C. In this case, not only the polymerization of the adhesive and the mutual diffusion of the films occur, but also the stabilization of the properties of the coating.

Then a second thin layer of glue is applied, dried in air, and a second layer of nylon with a 3% solution in formic acid. The plate is again subjected to hot drying, after which the output parameter of the transducer is checked - its dynamic resistance Rc in dry air. If it is small, additional layers of glue and nylon are applied until Rc becomes equal to 1,2 ± 0,1 kOhm.

The described technology makes it possible to obtain humidity sensors that are reproducible in terms of operational parameters. They have a linear conversion characteristic, low inertia and temperature error.

On the basis of this sensor, a pocket hygrometer (Fig. 2) was created, capable of controlling air humidity within the range of 20...95% with an accuracy of ±1%. Schematic diagram of the instrument's measuring unit is shown in fig. 3.

Sensor BQ1 is included in one of the arms of the measuring self-balancing bridge operating at a frequency of 300 kHz, in series with a compensation element containing resistor R1, capacitor C1 and varicap VD1. Trimmer resistor R5 is used to set the bridge mode, for example, when replacing the converter. The output of the bridge through the capacitor C2 is connected to its input through an amplifier based on transistors VT1, VT2 and a phasing transformer T1.

The capacitance of the VD1 varicap (from the KV102, KV104 or similar series) without supplying a control DC voltage is maximum, and the active resistance at a frequency of 300 kHz is minimum. For this reason, the active resistance of the VD1R1 circuit at a frequency of 300 kHz is also minimal. As a result, the condition of self-excitation of the amplifier is fulfilled: the active resistance of the measuring arm of the bridge is less than the resistance of the comparison arm, the bridge is unbalanced, its output voltage is maximum. After current amplification by an emitter follower on a VT3 transistor, it enters the input of a detector made according to a voltage doubling circuit (diodes VD4, VD5). The resulting DC voltage is fed to an analog-to-digital converter with a liquid crystal display. The converter and indicator are made according to the standard scheme, therefore, in fig. 3 are not shown. Resistor R17 regulates the limits of controlled humidity.

The SB1 switch selects the "Operation" or "Control supply voltage" mode (which is supported by the resistor R16).

Thus, simultaneously with receiving an informative signal determined by a change in the dynamic resistance of the converter, which, in turn, depends on humidity, automatic self-balancing of the bridge is provided: the high-frequency voltage from the variable resistor R15 is supplied to the detector (diodes VD2, VD3) and through the resistor R6 to compensation element (VD1R1C1). The output constant voltage of the detector controls the active resistance of the compensation element, and changing the capacitance of the varicap VD1 implements automatic balancing of the bridge.

When the power is turned on, the active resistance of the compensation element is minimal, which ensures self-excitation of the amplifier due to the unbalance of the bridge. Then a constant control voltage, depending on the degree of unbalance, changes the resistance of the compensation element, reducing the resistance of the measuring arm of the bridge and bringing it closer to the resistance of the comparison arm.

Full balance of the bridge does not occur, since in this case self-oscillations are not excited. But with the gain of the amplifier Ku > 1000, the unbalance of the bridge is negligible (about 10 ohms). This mode of operation of the measuring bridge provides the secondary converter with high stability and the necessary sensitivity, regulated by resistor R15.

The device is powered by a battery "Krona" (GB1), connected to the toggle switch SA1. The current consumed from the source is 2...3 mA.

The transformer is made on a magnetic circuit of size K12x5x5 from M1000NM-A ferrite. Windings I and II contain 90 and 35 turns of PELSHO 0,01 wire, respectively. Winding I with capacitor C4 form a resonant circuit tuned to a frequency of 300 kHz. With the correct phasing of the transformer windings, a positive feedback occurs.

Quartz dissipative converters of mechanical energy have found a very wide application. They are used to measure the rheological properties of human blood in the diagnosis of diseases [6], the viscoelastic properties of polymers, determine the temperature of phase transitions in liquid crystals, and other important parameters.

Note that the method for studying viscoelastic coatings of quartz plates was developed by us earlier than foreign scientists. They use for this purpose the cutoff piezoelectric element AT, which is less informative than DT.

The magazine "Radio" [7] published a photograph of an exhibit from the all-Union radio exhibition used to indicate the presence of water in aviation fuel (authors V.E. Savchenko and N.I. Lobatsevich, Ivanovo). It is known that dissolved water (thousandths of a percent) in the fuel freezes with decreasing temperature and, precipitating, can clog fuel filters, which can cause an aircraft accident. This device has been successfully used at airfields. It implements the invention [8], which marked the beginning of the use of evacuated quartz resonators in dissipative electrical energy converters to control the scattering parameters of dielectrics. Such devices are called quartz dielcometers.

From the consideration of the equivalent circuit of the quartz resonator in [1], it can be seen that when excited at the frequency of the series resonance, its dynamic inductance and capacitance are mutually compensated. If a capacitive sensor LED is connected in series with the resonator, the resonator is detuned relative to the resonant frequency and the dynamic resistance increases due to incomplete compensation of the inductive resistance by the capacitive ones. Complete compensation is prevented by the interelectrode capacitance Co of the resonator.

The value of the active resistance R of the resonator-capacitive sensor circuit can be calculated by the formula

If there are dielectric losses in the capacitive sensor, determined by the resistance Rd, the active resistance of the sensor Ra.d should be added to the resistance R, which is associated with the dissipation of the electric field energy in a controlled environment where the sensor is located:

Partial compensation of the capacitive resistance of the sensor by the inductive resistance of the resonator makes it possible to measure very small active losses in dielectrics.

Known devices with oscillatory circuits containing a coil and a capacitor cannot reliably control small dielectric losses. So, the E4-7 Q-meter at a frequency of 50 kHz can measure the active resistance of not more than 100 MΩ and with an error of ±5%.

Determination of active resistance using a dissipative transducer does not require manual tuning for resonance. The measuring bridge is automatically self-balancing in the same way as described above (fig. 3). It can easily control active resistance up to 10 GΩ with an error of no more than ±1% with a sensor capacitance of 4 pF at a frequency of 50 kHz. With a 1 pF sensor it will be possible to measure loss resistances greater than 100 GΩ. Thus, the described transducer significantly expands the possibilities of studying new materials with low losses.

On its basis, quartz moisture meters VK-2 were created and adopted by the State Commission, which are used in textile production to control and regulate the humidity of moving textile materials and semi-finished products. Unlike foreign devices of similar purpose by Mahlo, the VK-2 moisture meter controls with high accuracy the moisture content of materials made of synthetic fibers, which are characterized by low moisture absorption and dielectric losses.

In the VK-2 device, there is no roller with a brush contact rolling over the fabric. It is replaced by an air capacitor with a capacity of approximately 150 pF, formed by a stationary cylinder connected to the instrument and a cylinder rolling over the material being tested. Between the cylinders there is an air gap of about 0,5 mm. The recent modernization of the moisture meter with the transition to a new elemental base made it possible to improve its characteristics. The new IVK-4 device simplifies the operation procedure.

A portable device has been developed to control the moisture content of bulk materials, for example, grain, seeds of cucumbers, tomatoes, etc. It controls the moisture content of such objects in the range of 2 ... 30%. The absolute error does not exceed ±1% at humidity up to 15% and ±1,5% at 15% and more. The use of an inductive sensor in a dissipative transducer made it possible to create a flaw detector for detecting hidden defects in carbon fiber reinforced plastics used at important industrial facilities.

Important results were obtained in the study using an ice active resistance transducer, which confirmed the possibility of registering not only water in liquid fuel, but also ice at temperatures up to -50 °C.

Literature

1. Belykh A. Quartz filters for transfers. - Radio, 2002, No. 7, p. 64-67.
2. Savchenko V. Energy method for measuring non-electric quantities using quartz resonators. - Engineering Physics Journal, 1997, No. 1, p. 163-167.
3. Savchenko V. E., Gribovv L. K. Gas humidity sensor. Description of the invention to the author's certificate No. 1003003. - Bulletin "Discoveries, inventions, 1983, No. 9.
4. Savchenko V. Quartz gas humidity sensors. - Radio, 1975, No. 11, p. 26, 27.
5. Gribova L. K., Savchenko V. E. A method of manufacturing a piezoquartz gas humidity sensor. RF patent No. 2035731. - Bulletin "Discoveries, inventions, ...", 1995, No. 14
6. Savchenko V. E. et al. Sensor for monitoring the rheological properties of blood. Description of the invention to the author's certificate No. 1399686. - Bulletin "Discoveries, inventions, ...", 1988, No. 20.
7. Lysikov A. Amateur radio contribution to the national economy. - Radio, 1987, No. 11, p. 47, 48.
8. Savchenko VE A device for measuring the parameters of dielectrics. Description of the invention to the author's certificate No. 321770. - Bulletin "Discoveries, inventions, ...", 1971, No. 35.
9. Savchenko VE Parametric converter of small moisture content of dielectrics into an electric signal. RF patent No. 1049816. - Bulletin "Discoveries, inventions, ...", 1983, No. 39

Author: V.Savchenko, L.Gribova, Ivanovo

See other articles Section Radio amateur designer.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

A New Way to Control and Manipulate Optical Signals 05.05.2024

The modern world of science and technology is developing rapidly, and every day new methods and technologies appear that open up new prospects for us in various fields. One such innovation is the development by German scientists of a new way to control optical signals, which could lead to significant progress in the field of photonics. Recent research has allowed German scientists to create a tunable waveplate inside a fused silica waveguide. This method, based on the use of a liquid crystal layer, allows one to effectively change the polarization of light passing through a waveguide. This technological breakthrough opens up new prospects for the development of compact and efficient photonic devices capable of processing large volumes of data. The electro-optical control of polarization provided by the new method could provide the basis for a new class of integrated photonic devices. This opens up great opportunities for ... >>

Primium Seneca keyboard 05.05.2024

Keyboards are an integral part of our daily computer work. However, one of the main problems that users face is noise, especially in the case of premium models. But with the new Seneca keyboard from Norbauer & Co, that may change. Seneca is not just a keyboard, it is the result of five years of development work to create the ideal device. Every aspect of this keyboard, from acoustic properties to mechanical characteristics, has been carefully considered and balanced. One of the key features of Seneca is its silent stabilizers, which solve the noise problem common to many keyboards. In addition, the keyboard supports various key widths, making it convenient for any user. Although Seneca is not yet available for purchase, it is scheduled for release in late summer. Norbauer & Co's Seneca represents new standards in keyboard design. Her ... >>

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Random news from the Archive Plant for cleaning the air from carcinogens 23.06.2020 Researchers at the University of Washington have created a genetically modified houseplant that absorbs chloroform and benzene molecules from the air, using them to support its own growth. Scientists have turned scindapsus or "devil's ivy" into a biological filter that can fight the smallest particles that are not captured by traditional air purification equipment. The unique capabilities of the plant are due to the fact that it was added a gene responsible for the formation of the cytochre P450 2E1 protein, which is usually produced by the liver of mammals to neutralize toxins. With its help, the body converts benzene into phenol, and chloroform into carbon dioxide and chloride ions. Harmful carcinogens accumulate in homes and can cause cancer. However, the modified scindapsus not only neutralizes them, but also uses them for growth. The plant feeds on carbon dioxide and chloride ions, and forms components of cell walls from phenol. During the tests, samples of conventional and GM ivy were sealed for 11 days in test tubes with contaminants. In test tubes with ordinary scindapsus, the concentration of gases did not change over time. However, the modified plants reduced the concentration of chloroform by 82% in just three days, and almost completely absorbed it on the sixth day. Although a little slower, but the content of benzene also decreased: by 75% by the eighth day. Despite the excellent performance, filtration is passive, so air circulation is required for effective cleaning. If the plant just stands in the corner of the room, it will certainly clean up the surrounding area, but without a directed flow, it will take a long time for harmful particles from the other side of the room to get on the leaves. Therefore, for quick filtration, it is necessary to place the scindapsus under a fan that drives air through its leaves. Scientists are also working on methods to combat other harmful gases. A Rutgers University team has created an electrocatalyst that turns CO2 into plastics, fabrics and resins.

Other interesting news:

▪ 2,5" 3TB Toshiba portable drives

▪ Single-chip system Qualcomm Snapdragon 855 Plus

▪ Diesel from petrol

▪ Benefit from biodegradable plastic questioned

▪ Old heart rejuvenated with stem cells

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Application of microcircuits. Article selection

▪ article by Ernst Haeckel. Famous aphorisms

▪ article What is quantum theory? Detailed answer

▪ car maintenance article. Standard instruction on labor protection

▪ article Security system MICROALARM. Encyclopedia of radio electronics and electrical engineering

▪ article Active load regulator with current stabilization, 8-28 volts 0,2-3 amperes. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024