RU2663552C1 - Method of pressure measurement - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to industrial metrology and can be used for high-precision measurement of static and dynamic pressure. Method of measuring the pressure at which in a cavity resonator in the form of a section of a waveguide with one of the end walls in the form of a metal membrane receiving the measured pressure, in the first measurement cycle, electromagnetic oscillations of one of its types H(n=0, 1, 2,…; m= 0, 1, 2,…, p=1 ,2,…) or E(n=0, 1, 2,…; m=1, 2,…, p=1, 2,…) with a nonzero index p and measure the resonant frequency ƒelectromagnetic oscillations. In addition, in the second measurement cycle, electromagnetic oscillations of the Etype are excited in this volume resonator with zero indices n and p and measure the resonant frequency ƒelectromagnetic oscillations, perform a joint functional transformation of resonant frequencies ƒand ƒ, the result of which is judged on the measured pressure.EFFECT: increase of functionality due to simplification of method realization and increase of measurement accuracy.1 cl, 1 dwg

Description

METHOD OF PRESSURE

The present invention relates to measuring technique and can be used for high-precision measurement of static and dynamic pressure.

A known method of measuring pressure and implementing its device (US 4604898 A, 08/12/1986). These technical solutions consist in the excitation of electromagnetic waves in a segment of a coaxial long line with an end sensitive element. By measuring the resonant frequency of the vibrations excited in this segment of the long line, the deflection of the deformable end wall of the resonator is determined. In the device, the end sensing element is a capacitor formed by a combination of a flat metal plate connected to the inner conductor of the coaxial line and installed perpendicular to its longitudinal axis, and parallel to the plate of the deformable end wall (membrane), which receives external pressure. Also known is a device for measuring pressure, containing a coaxial resonator, at the end of which there are two flat disks that perform the function of a capacitor. One of these disks is attached with a rod to the center of the membrane that accepts the measured pressure, and the other disk is fixed to the end of the inner conductor of the coaxial line parallel to the first disk (RU 2221228 C2, 10.01.2004).

There is also known a method and device (US 3927369 A, 01/31/1973), according to which electromagnetic waves are excited into a microwave (microwave) sensing element in the form of a volume microwave resonator, which has an elastic end wall (membrane, diaphragm, etc.), and measure the resonant frequency of electromagnetic waves of this resonator. The device comprises a volume microwave resonator and a unit connected to it for generating a resonant frequency of electromagnetic waves of the resonator and a unit for measuring the resonant frequency of the resonator. The output of this unit corresponds to the measured pressure. This frequency is usually of the order of several gigahertz and depends on the size of the resonator, the selected "working" type of electromagnetic waves. In this case, a change in pressure leads to a displacement of the flexible cavity wall (this is its end wall), changing the longitudinal size of the cavity of the resonator and, as a consequence, its resonant frequency.

There is also known a method of measuring pressure, according to which electromagnetic waves are excited in two volume resonators and the resonance frequency of each of them is measured (WO 2004088266 A1, 03/26/2004). In this case, one of the volume resonators has an elastic wall, which is affected by the measured pressure, and the other resonator is a reference, located together with the first resonator at the same ambient temperature, but not subject to the influence of the measured pressure. The joint functional transformation (subtraction of one from the other) of the measured resonant frequencies of both resonators makes it possible to reduce the effect of temperature changes on the pressure measurement result of the first resonator. The disadvantage of this method is the complexity of its implementation, due to the need to use two volume resonators. In addition, the temperature at which these volume resonators are located may in principle be somewhat different, which leads to some error in the measurement of pressure during the indicated joint conversion of the resonance frequencies of two volume resonators.

A technical solution is also known (Viktorov V.A., Lunkin B.V., Sovlukov A.S. Radio wave measurements of technological process parameters. M.: Energoatomizdat. 1989. 208 pp. 118-120), which is the most technical close to the proposed method and adopted as a prototype. According to this method of measuring pressure, in the first cycle of measurements in a volume resonator from one of the end walls in the form of a metal membrane perceiving the measured pressure, electromagnetic waves are excited on one of its types Н _nmp (n = 0,1,2, ...; m = 0,1,2, ..., p = 1,2, ...) or _Еnmp (n = 0,1,2, ...; m = 1,2, ..., p = 1,2, ...) with a non-zero longitudinal index p and measure its resonant frequency ƒ _{1 of} electromagnetic oscillations, depending both on the measured pressure and on temperature - a disturbing factor that reduces the accuracy of pressure measurement .. In the second cycle of Measurements excite electromagnetic oscillations of type Е ₀₂₀ with a zero longitudinal index p in this resonator and measure the resonant frequency ƒ _{2 of} electromagnetic oscillations, which depends only on temperature. The joint functional transformation when implementing a differential measurement scheme (subtracting ƒ ₁ from ƒ ₂ ) of the measured resonant frequencies ƒ ₁ and ƒ ₂ allows to reduce the effect of temperature changes on the pressure measurement result.

The disadvantage of this method is the difficulty of its implementation, due to the need to excite the cavity resonator in the second measurement cycle on one of the highest types of vibrations, namely E ₀₂₀ , for which it is necessary to take measures to isolate (filter) this higher type of vibrations and measure the corresponding resonant frequency ƒ ₂ . In addition, with possible significant temperature changes in the values of permittivity ε and μ, respectively, of the medium in the cavity of the resonator, the measurement accuracy remains low due to the application of the prototype method (and other known technical solutions) of the differential frequency conversion circuit scheme ƒ ₁ from ƒ ₂ , which does not allow in this case (with significant changes in ε and (or) μ) to completely exclude the influence of possible temperature changes in ε and (or) μ on the pressure measurement results.

The technical result of the present invention is to simplify the implementation of the method and increase the accuracy of the measurement.

The technical result is achieved by the fact that in the proposed method of measuring pressure, in which in the volume resonator in the form of a segment of a waveguide from one of the end walls in the form of a metal membrane perceiving the measured pressure, electromagnetic oscillations of one of its types are excited in the first measurement cycle Н _nmp (n = 0,1,2, ...; m = 0,1,2, ..., p = 1,2, ...) or Е _nmp (n = 0,1,2, ...; m = 1,2, ..., p = 1,2, ...) with non-zero index p and the measured resonance frequency ƒ ₁ electromagnetic oscillations, additionally, in a second measurement cycle, excite the cavity resonator lektromagnitnye oscillation type E ₀₁₀ with zero indices n and p and the measured resonance frequency ƒ ₂ electromagnetic oscillations producing a joint functional transformation of the resonance frequencies ƒ ₁ and ƒ _2, the result of which is judged on the measured pressure.

The proposed method is illustrated by the drawing in FIG. 1, which shows its structural diagram of a device for its implementation.

In FIG. 1 shows a cavity resonator 1, a metal membrane 2, a communication element 3, a switch 4, an electronic unit 5, a functional converter 6, a recorder 7.

The essence of the proposed method is as follows.

According to this method, electromagnetic waves are excited in a cylindrical volume resonator 1 in the form of a segment of a circular waveguide having a thin metal membrane 2 at one of its ends (Fig. 1). When an external effect of any physical quantity (in Fig. 1, such an action is shown by an arrow) or when this effect changes relative to its initial value, the metal membrane 2 of the cavity resonator 1 deflects, thereby ensuring that the corresponding pressure P is perceived (due to deflection measurements). An informative parameter is the resonant frequency of electromagnetic oscillations in this volume resonator, which is a function of the deflection of the membrane, more precisely, of its central part relative to its initial position, corresponding to the absence of an external influence of a physical quantity (or a change in this effect relative to its certain initial value).

In the proposed method, two successive measurement cycles are carried out using the same cylindrical cavity resonator. The electromagnetic oscillations of the possible types are H _nmp (n = 0,1,2, ...; m = 0,1,2, ..., p = 1,2, ...) and Е _nmp (n = 0,1,2, ...; m = 1,2, ..., p = 1,2, ...) in a cylindrical volume resonator are characterized by the values of three indices n, m and p, which are included in the expressions for the components of the electric and magnetic fields and the natural (resonance) frequencies of this volume resonator (Lebedev I .V. Microwave Engineering and Instruments. T. 1. M: Higher School. 1970. S. 78-89). The indices n, m, and p characterize the periodicity of the field (the number of half waves) according to the polar angle, radius (i.e., the number of full and incomplete half waves that fit from the axis to the wall of the cylindrical resonator), and the length of the cylindrical resonator.

In the first measurement cycle, electromagnetic oscillations of one of its types H _nmp or Е _{nmp are} excited in the volume resonator 1 with a non-zero longitudinal index p and the resonant frequency ƒ _{1 of} electromagnetic oscillations is measured. Since p ≠ 0, this resonant frequency ƒ ₁ is a function of the length of the cavity resonator (Lebedev I.V. Technique and microwave devices. T. 1. M.: Higher school. 1970. S. 342-349):

- значения, соответственно, корней функции Бесселя для волн типов Е_nm и ее производной для волн типов Н_nm, с - скорость света, ε и μ - соответственно, относительное значение диэлектрической и магнитной проницаемости среды в полости резонатора, а - радиус цилиндрического резонатора,

- длина этого резонатора.where v _nm and

are the values, respectively, of the roots of the Bessel function for waves of types E _nm and its derivative for waves of types H _nm , c are the speed of light, ε and μ are, respectively, the relative value of the dielectric and magnetic permeability of the medium in the cavity of the resonator, and is the radius of the cylindrical resonator,

is the length of this resonator.

цилиндрического резонатора 1 определяется величиной прогиба деформируемой металлической мембраны 2, зависящей от измеряемого давления. Величина прогиба этой торцевой стенки (мембраны) выражается следующей формулой (US 3927369 А, 31.01.1973):Length

cylindrical resonator 1 is determined by the magnitude of the deflection of the deformable metal membrane 2, depending on the measured pressure. The magnitude of the deflection of this end wall (membrane) is expressed by the following formula (US 3927369 A, 01/31/1973):

where ΔР is the pressure difference from the outer and inner sides of the membrane, a is the radius of the cylindrical membrane, d is its thickness, E is the elastic modulus of the specific material of which the membrane is made. Formula (2) expresses the maximum strain in the center of the membrane. The design of the cavity resonator can be made of copper, brass and other metals with a small resistivity. The elastic end wall (membrane) can be made of various metals, for example, elinvapa (RU 2221228 C2, 10.01.2004). It is permissible to choose stainless steel as the material for the membrane. The thickness of the membrane can be 0.1 ÷ 0.2 mm, and its diameter should correspond to the diameter of the cylindrical resonator, for example, 10 ÷ 40 mm.

Then, additionally, in the second measurement cycle, electromagnetic oscillations of one of its types E _nm0 , in particular the lowest type E ₀₁₀ , with zero indices n and p are excited in the same volume resonator 1 and the resonant frequency of electromagnetic oscillations is measured:

волны E₀₁ в круглом волноводе и не зависящей от длины

(т.е. от величины прогиба металлической мембраны):Oscillations of the E ₀₁₀ type are the lowest type of electromagnetic oscillations among the E _nm0 types and are characterized by the lowest resonant frequency ƒ ₂ equal to the critical frequency

wave E ₀₁ in a circular waveguide and independent of length

(i.e., the magnitude of the deflection of the metal membrane):

It should be noted that in a cylindrical resonator, the first index n can be equal to zero for both types of vibrations Е _nmp and Н _nmp. The last index p can be equal to zero only for oscillations of types E _nmp , that is, oscillations of only types E _nm0 are possible. That is, in a cylindrical resonator, the presence of oscillations of the types _Еn0p , _Нn0p and Н _{nm0 is impossible} (Grossman Yu.S. Theoretical foundations of radio engineering. Minsk, MVIRTU publishing house. 1960.442 p. 367-376).

(т.е. от величины прогибы торцевой мембраны), а зависит, как и резонансная частота ƒ₁, от температуры окружающей среды (при этом ƒ₁ зависит от величины измеряемого давления, влияющего на степень прогиба торцевой мембраны 2). Проведение измерений во втором цикле на низшем типе колебаний Е₀₁₀ с нулевыми индексами n и p, характеризуемых наименьшим значением резонансной частоты ƒ₂, упрощает процесс выделения этого типа колебаний и проведения измерений ƒ₂.In the second measurement cycle, electromagnetic waves are excited in a cylindrical resonator 1 of the lowest type of oscillation E ₀₁₀ , when the resonant frequency ƒ ₂ is independent of the length

(i.e., the magnitude of the deflection of the end membrane), and, like the resonance frequency ƒ ₁ , depends on the ambient temperature (in this case, ƒ ₁ depends on the measured pressure, which affects the degree of deflection of the end membrane 2). Carrying out measurements in the second cycle on the lowest type of oscillations E ₀₁₀ with zero indices n and p, characterized by the lowest value of the resonant frequency ƒ ₂ , simplifies the process of isolating this type of oscillation and taking measurements ƒ ₂ .

Performing a joint functional transformation of the resonant frequencies ƒ ₁ and ƒ ₂ , its result is used to judge the measured pressure with a significant decrease in the effect of ambient temperature on the result of pressure measurement. So, the circuit of the device that implements this method, with the determination of the difference ƒ ₁ and ƒ ₂ (differential circuit) can significantly reduce the influence of temperature. Also, in another embodiment of the joint conversion of the resonant frequencies ƒ ₁ and ƒ ₂ , their functional (ratiometric) conversion in the functional block of the device that implements this method, as follows from formulas (1) and (3), according to the relation ƒ ₁ / ƒ ₂

соответствуют проведению измерений в первом и втором тактах.during the measurement process ensures the invariance of the pressure measurement results to possible changes, including temperature, of the ε and μ values characterizing the medium in the cavity of the cavity resonator. Here the indices "1" and "2" at v _nm and

correspond to measurements in the first and second measures.

Note that, as seen from the consideration of formulas (1), (3) and (4), the application of a differential measurement scheme with the determination of ƒ ₁ - ƒ ₂ does not eliminate the dependence of such a frequency conversion on the quantities ε and μ and, therefore, on the influence their temperature changes to the pressure measurement result, which indicates an increase in measurement accuracy with possible significant changes in ε and (or) μ when applying the ratiometric conversion ƒ ₁ and ƒ ₂ .

In a device that implements this method, in a cylindrical volume resonator 1 having an end membrane 2 subjected to the influence of external pressure (shown by an arrow), electromagnetic waves are excited using a coupling element 3 (Fig. 1). Their excitation is carried out through the switch 4 using the electronic unit 5 sequentially in the first and second measurement cycles and in each of these cycles the electromagnetic waves are taken using the coupling element 3 and the corresponding resonant frequency ƒ ₁ and ƒ _{2 are} measured in the electronic unit 5. The values ƒ ₁ and ƒ ₂ are input to the functional converter 6 for their joint conversion (differential or ratiometric conversion). A recorder 7 is connected to its output to determine the magnitude of the measured pressure.

Thus, in this method of measuring pressure, simplification of its implementation and increase of measurement accuracy are achieved.

Claims (1)

A method of measuring pressure, in which in the first resonator in the form of a segment of a waveguide from one of the end walls in the form of a metal membrane perceiving the measured pressure, electromagnetic oscillations of one of its types are _excited N _nmp (n = 0, 1, 2, ... ; m = 0, 1, 2, ..., p = 1, 2, ...) or _Еnmp (n = 0, 1, 2, ...; m = 1, 2, ..., p = 1, 2, ...) s non-zero index p and measure the resonant frequency ƒ _{1 of} electromagnetic waves, characterized in that in addition, in the second measurement cycle, type E electromagnetic waves are excited in this volume resonator ₀₁₀ with zero indices n and p and measure the resonant frequency ƒ _{2 of} electromagnetic waves, produce a joint functional transformation of the resonant frequencies ƒ ₁ and ƒ ₂ , by the result of which the measured pressure is judged.

Images