SU746219A1 - Pressure sensor with frequency output - Google Patents

Description

(54) PRESSURE SENSOR WITH FREQUENCY OUTPUT

one

The invention relates to instrumentation engineering and can be used in instruments for measuring pressure.

Frequency pressure sensors are known with resonators in the form of flat, round-shaped elastic plates separating the internal volume of the sensor: into two mirror-symmetric pneumatic chambers communicating with a controlled gaseous medium. These pneumatic chambers have the form of slot gaps between the surfaces of the resonator and the surfaces of the body parts of the sensor facing them, and the magnitude of these gaps is chosen so that the time constant of the pneumatic chambers exceed the half-period of the oscillations of the resonator. In order to ensure the dynamic balance of the oscillatory system of the sensor and, consequently, its high quality factor, a lower form of fan-shaped bending oscillations is excited in the resonator (i.e., an oscillation mode characterized by the presence of two nodal diameters in the absence of nodal circles) 1.

In this sensor, the antinodes of oscillations fill the area of the resonator circle.

completely, which does not allow to reduce its dimensions.

The closest to the offer is a sensor whose resonator,

5, which is a flat elastic plate, divides its internal volume into two mirror-symmetric pneumocameras communicating with the controlled medium. Pneumatic chambers

10 is made in the form of slot gaps between the surfaces of the resonator plate and the flat surfaces of the sensor body parts facing the resonator. The amount of gaps playing

5, the role of pneumocameras is chosen so small that the time constants of these pneumocameras exceed the half-period of the resonator oscillations. On both sides of the resonator, electrodes of capacitive excitation systems and removal of its oscillations are symmetrically located. Both the contours of the entire resonator plate as a whole, and all the coinciding parts of the contours limiting the free

25 and the rigidly fixed region of the resonator plate, have a common axis of rotational symmetry in the order of 2 n (where n is the number of nodal diameters) and 2 n common symmetry planes passing through this axis. The electrodes of the capacitive systems of the web and of the oscillations of the resonator have the form of sectors that are different from each other on both sides of the elastic plate, 2p electrodes from each side, and are characterized by the same symmetry elements 2j.

The disadvantage of the sensor lies in the fact that the reduction of overall sprays is limited by the need to locate the antinodes so that they have a common axis of rotational symmetry in the order of 2n.

The purpose of the invention is to reduce the size of the sensor.

This goal is achieved by the fact that the resonator is made in the form of a rectangle fixed on two pairs of supports, each of which is made in the form of elastic tubes arranged along different sides of the resonator.

FIG. 1 shows the structure of the proposed sensor, general view; in fig. 2 — intermediate assembly of the sensing element assembly; on . 3 - the lowest form of bending oscillations excited in the resonator; in fig. 4 is a circuit diagram of the sensor.

The sensor is assembled in a flexible case formed by a segment of a cylindrical tube 1, at the end of which there is a glass insulator 2 with pressure seals 3. The other end of the tube 1 of the hermetic body is connected to a vacuum joint (welding, soldering) 4 with fitting 5, which serves supply to the sensor gaseous controlled environment. Inside the housing 1 is placed the node of the sensing element assembled in coaxial 6 (see fig. 2). In addition to the casing with technological windows.

The sensing element node includes two gas-tight screens 8 made of a dielectric with high mechanical properties (for example, ceramics 22 CS), a resonator 9, which is an elastic flat plate of a rectangular shape with a ratio of the short side to the long no more than 1: 4, and four roller bearings 10, made in the form of thin-walled elastic tubes.

Gas-tight Screens 8 have in cross-sectional view of a circular segment. Flat surfaces of screens 8 facing the resonator are applied thin film electrodes 11-16 (see Fig. 4 of electrostatic systems of excitation and vibration pickup of resonator 9. At distances of 0.225 + ± 0.05 resonator lengths on the screens

8 there are paei 17 triangular cross-section ..

On the semicircular cylindrical surface of the shields B., longitudinal grooves 18 are cut, which are used for wiring, using a second one. electrodes 11-16 are included in the sensor circuitry.

When assembling the sensing element assembly, screens 8 with resonator 9 located between them are inserted inside the casing 6, after which elastic roller supports 10 placed in triangular grooves are installed through technological windows 7 between screens 8 and resonator 9. By deforming (see Fig. 1), the roller bearings clamp the resonator 9, thus providing its elastic fastening along the node lines of the chosen vibration mode (see Fig. 2).

The electrical circuit of the sensor (FIG. 4) includes; The electrodes 11-13 of the resonator excitation system of the resonator 9, the electrodes of the oscillation pickup system 14-16, high-resistance impedances 19, the bias sources 2 separation capacitors 21 and the wideband amplifier 22 of the self-excitation system.

The electrodes 11-13 of the excitation system, the electrodes 14-16 of the removal system, through high-resistance impedances 19, are connected to sources of constant bias 20, and through coupling capacitors 21 to the output and input of a broadband amplifier 22 of the self-excitation system, respectively. The magnitude of the resistances 19 is chosen in such a way that the time constant of the RC chain, including one of the resistances 19 and the capacitance formed by a group of three elevens 11-13 (or 14-16) connected in parallel to this resistance and the resonator 9, is significantly longer than half a period oscillations of the resonator. Purpose separation capacitors

21 is the amplifier protection

22 from falling into and out of relatively high dc voltages from constant displacement sources 20.

Together with the self-excitation system, the resonator forms an electromechanical self-oscillatory system, the frequency of which is close to the natural frequency of the chosen form (see Fig. 3) of the bending oscillations of the resonator. The resonator oscillation excitation system is formed by three electrodes 11–13, two of which (11 and 13) are facing the same side of the resonator 9 and are located opposite its end sections bounded by roller bearings 10, and the third (12) is facing the opposite side of the resonator and is located against its middle section (between the roller bearings 10). When an alternating electrical voltage is applied to the electrodes 11-13 from the output of the amplifier 22 of the system C1-1203, the wafers create a resonant distributed perpendicular plane of the excitation power, the direction of which changes to the opposite direction when passing through each of the KNOTS contact of the resonator 9 and roller supports 10), as well as when the polarity of the supply voltage is changed. The specified force causes the buildup of the chosen formulas of bending oscillations of the resonator. At the same time, on the other three electrodes — electrodes 14-16 of removal (forming a configuration representing a mirror image of the configuration in which electrodes llylS enter) —the electric signal arises, whose frequency is equal to, and the amplitude is proportional to the frequency and amplitude of the mechanical oscillations resonator 9. This signal through the separation capacitance enters the input of the self-excitation system amplifier 22. From the output of this amplifier, the amplified signal is fed through another separation capacitance 21 to a group of three excitation electrodes 11–13, thereby ensuring sustained oscillations of the resonator. The frequency of these oscillations will be close to the natural frequency f of the chosen form of bending resonator oscillations, which is determined by the formula „elastic modulus of the resonator material; h is the resonator thickness; p is the mass density of the resonator material; L is the length of the resonator; a is the size of the gap between the resonator and gas-tight screens; Р - measured pressure; Кр; К- - dimensionless numerical coefficients depending on Poisson's ratio. As follows from the above formula, the square of the frequency f of the output signal of the sensor depends linearly on the measurement

Claims (2)

746219 measured pressure P. This is due to the fact that the equivalent stiffness of the elastic system of the sensor depends not only on the parameters of the resonator itself, but also on the elasticity of the gas, located in the gap gaps between the surfaces of the resonator and the surfaces of gas-tight screens facing them. . Provided that the time constant of the process of changing the gas mass in the gap gaps significantly exceeds the half-period of free oscillations of the resonator (this is achieved by selecting a sufficiently small gap size), the gas in these gaps behaves as if they were sealed along the contours of antinodes. Poi. This effect of gas elasticity in the gap gaps on the equivalent stiffness of the elastic sensor system is proportional to the pressure P of this gas, which determines the linear dependence of the square of the oscillation frequency of the resonator on the measured {pressure. The linear arrangement of the antinodes, achieved when the resonator is made in the form of a rectangular plate with the ratio of the short side to the long side of not more than 1: 4, makes it possible to significantly reduce the overall dimensions of the sensor. Claims A pressure output sensor with a frequency output, comprising a flat resonator and vibration pickup and excitation systems, characterized in that, in order to reduce the envelope, the resonator in it is made in the form of a rectangle fixed on two pairs of supports, made in the form of an elastic pipe:. Sources of information taken into account in the examination 1. USSR author's certificate for application 2407562 / 18-10, cl. G 01 L 11/00, 20.10,76. 2. USSR author's certificate according to the application 2430018, class C. 01 L.11 / 00, 12.31.76 (prototype). 746219 fugues 3