RU2017100C1 - Pressure transducer - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: excessive pressure acts on the bottom hermetically connected with the casing through a bellows. The rod is rigidly linked with the bottom and diaphragm, which is deformed by the rod. The diaphragm is linked with a deformation-to-output signal converter and its area S_d is connected with effective area S_bell of the bellows by relation: S_bell > 1/4S_d. EFFECT: enhanced accuracy. 1 dwg

Description

 The invention relates to the field of measuring pressure and, in particular, hydrostatic pressure, the value of which determines the value of the liquid level.

 Known pressure sensors, the action of which is based on measuring the deformation of an elastic element that perceives the measured pressure. The elastic elements commonly used in pressure sensors are membranes, bellows, gauge tubular springs, etc. In these sensors, the deformation of the elastic element by means of a converter is transformed into a signal in a form convenient for further transformation, processing and storage.

 For example, in a pressure gauge - manometer [1], the pressure sensitive element is a membrane clamped at the edges. The transformer of membrane deformation (displacement of the center of the membrane) is a tape spring, to the central part of which is attached an arrow with a slider of the potentiometer. When pressure is applied to the membrane, its center moves, the tape spring unwinds and the arrow slider moves along the potentiometer. The magnitude of the change in potentiometer resistance is a measure of the measured pressure.

 The main disadvantages of these pressure sensors are the significant hysteresis of the sensor output due to friction in the kinematic diagram of the displacement transducer of the center of the membrane.

 Closest to the technical nature of the present invention is a pressure transducer measuring vibro-rod frequency type PDV [2] (hereinafter the transducer).

 In this device, a membrane that senses the measured pressure is used as a sensing element. A transformer of membrane deformations into an electrical signal is placed on the membrane, containing a flat jumper stretched between the two brackets, an exciter, an electromagnetic adapter, and an amplifier. The brackets are mounted on the membrane along its diameter at an equal distance from the center. To eliminate backlash in the joints and reduce hysteresis, the jumper and brackets are made in one piece with the membrane. All nodes (except the membrane) are enclosed in a sealed enclosure.

 The excitation and maintenance of oscillations of the jumper, performing the function of the resonator, is provided by the pathogen and an electromagnetic adapter mounted on both sides of the flat jumper. The amplifier supports jumper vibrations in self-oscillation mode. When the pressure changes, the membrane bends (deforms), the brackets diverge slightly and the jumper tension increases, thereby increasing the frequency of mechanical vibrations of the jumper and, accordingly, the output frequency of the converter. Thus, the value of the pulse repetition rate of the electrical pulses of the device is a measure of the magnitude of the pressure.

 The main disadvantage of the converter described above is its low sensitivity to pressure (hereinafter sensitivity). To increase the sensitivity, it is necessary to reduce the rigidity of the membrane, and this leads to a loss of rigidity of the system, consisting of a sensitive element - the membrane and the vibration system - brackets and jumpers. For this reason, PDV type pressure transmitters [2] have a minimum value of the upper limit of measurement equal to 1 MPa (or approximately 100 m water column). With a working range of measuring the frequency of oscillations of the jumper of the order of 1000 Hz for all ranges of pressure measurement, the maximum value of the pressure sensitivity of the sensor is 10 Hz / m water As the value of the upper limit of the pressure measurement increases, the sensitivity of the converter decreases accordingly.

 Since fluctuations in the water level in natural reservoirs (rivers, lakes, seas) usually do not exceed 10 m, PDV-type pressure transmitters produced by industry do not in some cases provide the necessary pressure sensitivity.

 The aim of the invention is to increase the sensitivity to pressure by increasing the deformation of the membrane from the measured pressure due to the concentration of the force acting on the membrane, while the rigidity of the membrane does not decrease and pressure measurement is provided in almost any small pressure range.

S_м (1)
Таким образом, предлагается воздействие на мембрану давления заменить на воздействие усилия, приложенного к центру мембраны.The goal is achieved by the fact that in the proposed pressure sensor containing a sensing element in the form of a membrane installed in a sealed housing with a bottom and a transformer of membrane deformations into an output signal, a rod and a bellows are introduced through which the bottom is hermetically connected to the body, while the membrane and the bellows are installed coaxially, the rod is rigidly fixed to the bottom center and the membrane, and the effective area of the bellows S _sp and the area S _m membranes are related by:
S _sf >

S _m (1)
Thus, it is proposed that the pressure on the membrane be replaced by the force applied to the center of the membrane.

 In this case, changing the effective area of the bellows receiving the measured pressure, you can change the sensitivity of the sensor by pressure.

, (2) где ω_o - прогиб центра мембраны;
μ - коэффициент Пуассона;
R - радиус мембраны;
E - модуль упругости материала мембраны;
h - толщина мембраны.Indeed, the deflection of the center of a flat round membrane characterizing the deformation of the membrane from the pressure P acting on the membrane is determined by the expression
ω _o =

, (2) where ω _o is the deflection of the center of the membrane;
μ is the Poisson's ratio;
R is the radius of the membrane;
E is the elastic modulus of the membrane material;
h is the thickness of the membrane.

(2^I)
С другой стороны, прогиб центра плоской круглой мембраны от усилия F, приложенного в центре мембраны перпендикулярно к ее плоскости, определяется выражением
ω_o= 0,68

(3)
Таким образом, если давление Р, воздействующее на круглую мембрану радиуса R, сконцентрировать и приложить к центру мембраны, то возникает усилие, равное
F=Pπ R², (4) которое вызовет перемещение центра мембраны на величину

= 0,68

= 0,68

(5) (что получается после подстановки выражения (4) в формулу (3)).Given that for a metal the Poisson's ratio μ = 0.3, we obtain the following calculated expression for the deflection of the center of the membrane from pressure:
ω _o = 0.17

(2 ^I )
On the other hand, the deflection of the center of a flat round membrane from the force F applied in the center of the membrane perpendicular to its plane is determined by the expression
ω _o = 0.68

(3)
Thus, if the pressure P acting on a round membrane of radius R is concentrated and applied to the center of the membrane, then a force equal to
F = Pπ R ² , (4) which will cause the displacement of the center of the membrane by

= 0.68

= 0.68

(5) (what happens after substituting expression (4) into formula (3)).

Comparing expressions (2 ^I ) and (5), we see that the deflection from the pressure P acting on a round flat membrane is 4 times less than the deflection of the same membrane from the force arising from the pressure P applied to the center of the membrane.

Therefore, if a bellow is installed coaxially with the membrane, it accepts the measured pressure, through which the bottom is hermetically connected to the body, and the center of the membrane and the center of the bottom are rigidly connected with the rod, then if the area of the measuring membrane is S _m = π R ² and the effective area of the bellows is S _sf ( S _m = S _sf ) the deflection of the center of the membrane will be 4 times greater than with the perception of the measured pressure directly by the membrane. In this case, to obtain the same value of the output signal from the transformer of membrane deformations, which occurs in the prototype from pressure P, it is enough to apply a pressure 4 times less in the proposed device, which corresponds to an increase in the sensitivity of the sensor also 4 times.

By varying the effective area of the bellows S _sph (relative to the diaphragm area S _m) can increase the sensitivity of the sensor at the desired value. So, with S _sf = 2S _m (or with an average bellows radius R _sf = 1.4 R _m ), the sensitivity of the proposed sensor will be 8 times higher than that of the prototype.

 The drawing shows a diagram of the proposed pressure sensor.

 The pressure sensor contains a sensing element in the form of a membrane 1 and a transformer for deforming the membrane into an output signal, which is made in the form of two brackets 2 and 3 installed along the diameter of the vibration jumper 4, stretched between the brackets 2 and 3, the exciter 5, the electromagnetic adapter 6 and the amplifier 7 The membrane and all elements of the membrane deformation transducer are placed in an airtight housing 8 with a cover 9 and a bottom 10. To ensure the stability of the sensor and reduce the hysteresis of its readings, membrane 1, brackets 2 and 3, the sliver 4 and the housing 8 are made in one piece.

S_м.In the sealed housing 8 with the bottom 10 coaxially with the membrane 1 installed bellows 11, through which bottom is sealingly connected to the housing, and a rod 12 rigidly secured to the centers of the bottom and a membrane, wherein the effective area of the bellows S _sp and the area S _m of the membrane are interconnected ratio S _sp>

S _m

 The membrane deformation transducer is electrically connected to a measuring system that provides secondary conversion of the transducer output signal, indication and recording of sensor readings. The measuring system is not shown in the diagram.

 The pressure sensor operates as follows.

When exposed to the measured pressure P on the bellows 11 to the center of the membrane 1 by a rod 12 F applied force equal magnitude PS _sp where S _sph - the effective area of the bellows 11. The force F deforms the membrane 1, the brackets 2 and 3 differ from each other by pulling the vibration jumper 4.

, (6) где А и В - постоянные коэффициенты, зависящие от конструктивных параметров датчика.The causative agent 5 of the oscillations, the electromagnetic adapter 6 and the amplifier 7 support the vibration jumper 4 in the self-oscillation mode, while the oscillation frequency f of the jumper is related to the measured pressure P by the expression
f = A

, (6) where A and B are constant coefficients depending on the design parameters of the sensor.

In case of equal effective area of the bellows 11 and S _sp membrane area S 1 _m, according to formulas (2 ¹⁾ and (5) moving the center of pressure of the membrane will be 4 times larger than for the case where the pressure P immediately perceived membrane 1. This allows 4 times reduce the effective area of the bellows 11, but at the same time get the same displacement of the center of the membrane 1, which is available for the prototype. In turn, this means that under the condition equation S = S _{m sp} sensitivity pressure sensor increases 4 times as compared with the prior art sensitivity.

S_м чувствительность датчика по давлению будет выше чувствительности прототипа и можно уменьшить, соответственно, величину верхнего предела диапазона измерения давления. Таким образом, с помощью предлагаемого датчика возможно измерение с высокой точностью колебаний уровня воды с диапазоном 10 м вод.ст. и менее. Существующие преобразователи давления типа ПДВ такой возможности обеспечить не могут.Therefore, under the condition S _sp>

S _{m the} pressure sensitivity of the sensor will be higher than the sensitivity of the prototype and you can reduce, respectively, the value of the upper limit of the range of pressure measurement. Thus, using the proposed sensor, it is possible to measure with high accuracy the fluctuations of the water level with a range of 10 m water column. and less. Existing PDV pressure transmitters cannot provide such an opportunity.

Claims (1)

PRESSURE SENSOR containing a sensing element installed in a sealed housing with a bottom in the form of a membrane and a transformer for deforming the membrane into an output signal, characterized in that, in order to increase sensitivity to pressure changes, a rod and a bellows are introduced into it, through which the bottom is hermetically connected to the housing , the membrane and the bellows coaxially mounted, the rod is rigidly fixed at the centers and the bottom membrane, and the effective area of the bellows S _sp and the area S _m membranes are related by
S _sf > 1/4 S _m .

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