SU883683A1 - Pressure converter with frequency output - Google Patents

Description

(54) PRESSURE TRANSMITTER G FREQUENCY

one

The invention relates to information-measuring equipment and is intended for measuring the absolute pressures of gaseous media.

A known pressure sensor with a frequency output, in which a thin-walled cylindrical resonator, made in the form of a cup, in which bending oscillations are continuously excited, is used as an elastic sensing element. The natural frequency of these oscillations is related to the measured pressure value and is the output parameter 1.

The closest in technical essence and achievable positive effect to the proposed invention is a frequency output pressure transducer device comprising a housing formed by elements of the excitation system with an internal cavity communicating with the controlled medium and a cylindrical resonator 2 fixed in its ends on the fastening elements.

A disadvantage of the known technical solution is the excitation of side mechanical resonances in the elements of the mounting - resonator, and the output.

which indicate the dependence of the output frequency on the measured pressure and that a; I am reducing the accuracy of measurement.

The purpose of the invention is to improve the accuracy and expand the range of pressure measurement.

This goal is achieved due to the fact that the resonator length does not exceed half the length of the radial-10 flexural wave, and the internal cavity is limited on the ends by the fastening elements made of elastic porous material permeable to the controlled medium.

15

Figure 1 shows a pressure transducer; Fig. 2 is a diagram of its connection to the drive system of the converter.

A thin-walled cylindrical resonator 1 made of an eline-welded alloy of a dielectric material with a corresponding metallization of surfaces, and body parts 2 and 3 of the excitation systems of oscillations of the resonator 1 form an internal cavity with their cylindrical surfaces, which is limited at the ends by elastic vibration dampers 4 and 5. Vibro supports 4 and 5 are elements for fastening the resonator 1 according to

its ends in the internal cavity of the transducer are coaxially cylindrical surfaces of body parts 2 and 3. Vibro supports 4 and 5 are made of a porous material permeable to the measured medium, for example, porous rubber. The electrodes b and 7 / placed on the case parts 2 and 3 are the elements of the excitation system, in particular electrostatic, and the pickup of the oscillations of the resonator. For connecting to the converter circuit, conductors 8, 9 and 10 are used. In this case, conductors 8 and 9 are fixed in the case parts 2 and 3 using insulating inserts 11 and 12. And the conductor 10 is made vibration-proof and passed through the vibration support 5. Mounted P The transducer can be installed in an additional case (non-shown) with electrical pressure sockets, for connection to the excitation system, and a choke, for connection to the volume, the pressure in which must be controlled.

The parameters of the vibration dampers 4 and 5, as well as their size, material, etc., are chosen from the condition of ensuring their elasticity is smaller (by an order of magnitude or more) than the elasticity of the cylindrical resonator 1.

The drive circuit of the converter (Fig. 2) is the circuit of the measuring oscillator. Electrode b is the receiving electrode of the converter and is connected via conductor 9 through a coupling capacitor 13 to a differentiating amplifier 14 with a high input impedance. The amplifier also contains an automatic gain control circuit. The output of amplifier 14 is connected via feedback capacitor 15 and conductor 8 to electrode 7, which plays the role of exciting the electrode. The power supply unit 16 supplies the polarization voltage to the receiving and exciting electrodes b and 7., respectively, through high-resistance resistors 1 and 18, and also provides the necessary supply voltage for the amplifier 14. Resonator 1 acting as a moving electrode of the electrostatic excitation system vibrations and their reception, with the help of the conductor 10 under the keys to the common electrical housing of the transformer. The outgoing frequency signal is removed from the output of Amplifier 14.

The operation of the transducer occurs as follows.

 When the supply voltage is applied from the power supply unit 16, a self-excitation of the converter occurs at the frequency of natural resonance oscillations of the resonator 1. At that, the AC signal from the receiving electrode through the conductor 9 and the capacitor 13

enters the amplifier 14, where it is amplified at the required number of times with a phase rotation of +90, which is necessary under the conditions of self-excitation of the switching circuit of the resonator 1. From the output of the amplifier 14, the electric signal is fed through the feedback capacitor 15 and the conductor 8 to the excitation electrode 7 of the converter excitation self-sustaining self-oscillations of the resonator 1. The automatic gain control circuit in the amplifier 14 provides the generation of oscillations within the linear range of the amplification of this amplifier, thus achieving the exception n Linear restriction transducer output signal.

The pressure of the controlled medium, penetrating through the pores in the vibration supports 4 and 5, leads to a change in the acoustic elasticity of the gas volume in the internal cavity of the sensor, which, in turn, changes the frequency of oscillation of the resonator 1, in accordance with the expression

ygKTPs;

EFF

where f is the output frequency of the converter;

ujp is the circular frequency of its own resonant axisymmetric radial oscillations of the resonator in a vacuum;

p controlled pressure of the gas medium;

with

the area of the cylindrical surface of the resonator, limited by the fastening elements - by vibration supports;

h is the average size of the internal cavity in the radial direction;

an indicator of adiabaticity or isothermality of the processes of gas compression-discharges in the internal cavity of the converter;

m

mass of the resonator and

EF-F Nena mass of elastic elements of the resonator mount - vibro support.

Since the cavity length was chosen not exceeding half the wavelength of the radial-flexural mode of oscillation of the resonator 1, in the described resonant system, due to bending elasticity, the individual elements of the resonator 1 cannot oscillate independently of each other. Therefore, with axisymmetric radial resonance, resonator 1 oscillates at all points with the same phase and amplitude, since a small deviation from this oscillation mode results in a bending wave along the cylindrical generator of the resonator 1, leveling the distribution of oscillations along the generator of the resonator cylinder and restoring the original auto-oscillation mode. This circumstance ensures the one-dimensionality of the compression processes of the gas medium in the internal cavity of the transducer in the radiographic direction, which eliminates the loss of shear viscosity and leads to an increase in the quality factor of the oscillatory system as a whole.

The presence of elastic fastening elements — vibration dampers 4 and 5, with low intrinsic elasticity, allows acoustic discharge of the resonator 1 and other transducer design elements, which reduces the excitation of side resonances in the oscillatory system and, thereby, increases the accuracy of pressure measurement.

Claims (2)

1. Pressure transmitter with frequency output, comprising a housing formed by the elements CHCt excitement, with an internal cavity, co-i communicating with the controlled medium, and fixed in. It is mounted on the fastening elements by a cylindrical resonator, characterized in that, in order to increase the accuracy and expand the pressure measurement range, the resonator length does not exceed half the length of the radial-bending wave, and the internal cavity is limited at the ends by the fastening elements made of elastic porous material, permeable to controlled environment. Information sources, 5 taken into account in the examination 1.Gorenstein I.A. Hydrostatic frequency sensors of primary information. M., Mechanical Engineering, 1976, p. 12-17. 2. USSR author's certificate 0 717581, class G 01 L 11/00 of 01/06/78 (prototype). Tl