SU1483297A1 - Method and apparatus for measuring pressure - Google Patents

Abstract

The invention relates to an instrumentation technique and permits an increase in the accuracy and an extension of the measurement range. The measured pressure acting on the diaphragm 3 is transmitted to the piston 4, and the piston presses on the separation fluid, which through the membrane of the opening 6 transfers the pressure of the piezometric fluid in the chamber 7. The state of the piezometric fluid changes, accordingly the optical signal arriving at the photodetectors 17 and 16. The signal then goes to the comparison circuit 19, showing the difference in the intensity of the scattered and transmitted light fluxes, which characterizes the measured pressure. 2 sec. and 1 h. the item of f-ly, 4 ill.

Description

j;

nineteen

W

§

(L

u

FIG H

located in the chamber 7. The state of the piezometric luminance changes, and the optical signal to the photodetectors 17 and 16 also changes accordingly. The invention relates to instrumentation and, in particular, to measurement methods and devices. pressure, and can be used, for example, to measure both the absolute value of the atmospheric pressure and its small deviations.

The aim of the invention is to improve the accuracy and the expansion of the measurement range.

Fig. 1 shows a phase diagram of a solution of n-propanol-water-sodium chloride with a double critical point; Fig. 2 is a plot of -., the intensity of the scattered light versus pressure at scattering angles of 90 °; FIG. 3 is a plot of the scattering factor of light in a solution versus pressure at scattering angles.

1-5 °; Figure 4 shows a device for measuring pressure, a general view.

When measuring the pressure of the proposed method, a solution with a double critical point is used as a liquid, the intensity of the scattered light is recorded, and the pressure value is determined from the ratio

-bcjp-p.),

where P0 is the pressure at which a liquid phase transition occurs}

f - measured pressure;

C is a constant determined by the choice of a particular solution with a double critical point;

B is constant depending on

scatter angle;

10 - light intensity, -created by the source;

1p - intensity of the scattered

Sveta.

Double critical point - point on the phase phase of the solution;

It steps on a comparison circuit 19, showing the difference in the intensity of the scattered and transmitted light fluxes, which characterizes the measured pressure. 2 sec. and 1 hp ff, 4 ill.

Q

50

five

0

Q

g

five

which is a fusion of two ordinary phase transitions of the second kind. In the case of liquid binary mixtures, systems are known whose heterogeneous (stratified) state is between upper TV and lower Tn critical temperatures (Fig. 1),

The most optimal mode of implementation of the method is the registration of intensely scattered at an angle of 1-5 ° to the optical axis of the luminous flux entering the liquid, i.e. in such angular limits, where the first interference maximum of the scatter ring structure is located, arising near the double critical point

In order to extend the range of the measured pressure, the registration of scattered light is conducted under the fragile 90 to the direction of the incoming light flux.

The method allows recording a pressure change with an average sensitivity of 10 atm. Moreover, when registering light scattering at an angle of 1-5 °, the sensitivity of the method increases by 100 times compared to the average sensitivity value, while scattering light at an angle of 90 °. The pressure measurement limit is increased to a value of 10 atm.

The device for the implementation of the proposed method (figure 4) consists of a housing with a lower thermostatic part. The upper part of the housing 1 by means of elastic plates 2 hermetically closes the diaphragm 3, which is connected to the piston 4. The latter enters the cylindrical sleeve 5 of the housing 1, in turn, is connected to the opening of the chamber 6, which is filled with a solution of n-propanol-water-sodium chloride. The hole is blocked by a membrane 7 of a polymer film, and the space of the sleeve 5 between the hole 7 membrane and the piston 4 is filled with a separating fluid. Camera 6 is made with 8-10 optical windows and

has built-in optical fibers 1 1. To prevent the air (bubble) from falling under the piston and to create the necessary initial hydrostatic pressure, a reservoir 12 with oil is installed on top of the cylindrical bushing 5. The valve 13 serves to regulate the working pressure in the chamber 6.

The device has a laser radiation source 14 installed in front of the entrance window 8, photodetectors 15 and 16 placed behind windows 9 and 10, respectively, and the diameters of the window 9 and the photodetector 14 are related to the distance of the latter to the scattering region ratios: d and 0,01712, at the radiation output from window 9, an additional photodetector 17 and an attenuator in the form of an aperture 18 are installed. The outputs of photodetectors 15, 16 and 17 are connected to a comparison unit 19.

The composition of the piezoelectric fluid is selected such that at a given temperature and initial pressure, the fluid is in a homogeneous state near the double critical point. The pressure acting on the diaphragm 3 is transmitted to the piston 4, freely moving in the space of the cylindrical sleeve 5. Moving when measuring pressure, the piston 4 presses on the separating fluid, which through the membrane 7 of the hole transfers the pressure of the piezometric fluid inside the chamber 6, creating her excess pressure. The condition of the piezometric liquid varies, and the optical signal applied to the photodetectors 16 and 16 changes according to this change. The signal from the photodetectors 15 and 17 goes to the comparison circuit 19, showing the difference in the scattered and transmitted light fluxes. . The latter is a reference signal for emitting a useful light signal 10. Such an inclusion scheme minimizes the effects of attenuating the scattered light near the double critical point, since attenuation of the scattered light is compensated for by attenuating the transmitted light. Thus, the imbalance signal of the comparison circuit is proportional to the applied pressure. When the photodetector 16 is in operation, the photodetector 17 does not work, and vice versa. The registration of light scattered at an angle of 1-5 ° is carried out by shielding the light rays at angles that satisfy the condition. The shielding of rays scattered at an angle of less than 1 ° is provided by the front (input) part of the photodetector located on the optical axis having an entrance aperture of 1 °. The shielding of rays scattered at an angle of more than 5 ° is provided by the size of the output window aperture of the housing - component five.

As can be seen from FIG. 3, the dependence of the values of the scattering coefficient 1/1 e R on the magnitude of the pressure change tends to infinity with (in equation (1) the constant B - 0). This circumstance makes it possible to record small pressure changes. Indeed, with a really achievable DR value of 0.1 atm, the DE / DR value is “2-U2 (FIG. 3) and, taking into account that the existing; The (differential) methods for detecting changes in luminous flux easily provide sensitivity in the determination of 10–10; the sensitivity of the method is obtained from the pressure P 10 - 10 Pa (0 6–10 7 atm).

When scattered at an angle of 90, the magnitude of the scatter remains finite (Fig. 2), which limits the pressure sensitivity to 10 atm. However, due to the absence of parasitic light from the walls of the optical fibers, which occurs when scattered from other angles, including small ones, makes it possible to observe scattering in a wider range of intensities (including low intensities), i.e. measure pressures in a wide range of 10 - I O3 atm. Restrictions on pressure at small angles arise for the following reasons: the lower limit (0L, 1 atm) - due to the fact that at these pressure values at given temperatures of double critical, point (45 ° C), the solution boils , the upper one is due to the presence of flare at small angles (reflections from the optical fiber walls), which is comparable in intensity to scattering at atm

With the mutually perpendicular distribution of the fibers of the input and output radiation, i.e. registering the light scattered under 90 ° with a sensitivity in determining pressure equal to atm, the range of measured pressures simultaneously expands to 10 a atm,

The invention can be used JQ under conditions of intense electromagnetic fields, in addition, the measurement of the augmentation is carried out using a compact small-sized device, 15

formula of invention

Claims (1)

1. A method of measuring pressure, which means that a light flux is passed through a liquid in a measuring chamber, is influenced by a measured pressure on a liquid, and judging by the change in intensity of the light flux, sensitivity, a solution with a double critical point is used as a liquid, the diffused JQ light flux is recorded at an angle of 1-5 to the optical axis of the light flux, and the value of the measured pressure is determined from the ratio 1o IP „H C (P - P0) + B, e P0 is the pressure at which the phase transition of the solution occurs; P - measured pressure; 40 C is a constant determined by the choice of a particular solution with a double critical point; B is constant, depending on the angle of the scattered light flux; Q 5 5 Q five 0 five IP is the intensity of the scattered light; 10 - the intensity of the light flux of the light source, 2, Method Pop.1, which differs from the fact that, in order to rescind the pressure measurement range, a light flux is recorded at an angle of 90 ° to the optical axis of the light flux. 3, a device for measuring pressure, comprising a housing inside which a measuring chamber filled with liquid is located with an inlet channel, the optical windows arranged coaxially with the light source and photodetectors being in the housing and the chamber, In order to increase the accuracy of pressure measurement, two light guides and a sensing piston were additionally introduced into the membrane, and the membrane was installed in the chamber at the inlet of the inlet channel, which was filled with separation fluid, and the piston is placed in the supply channel, the optical fibers are installed in the optical windows of the chamber, are located in the liquid and are placed with a gap relative to each other, whose values are within 20 µm - 10 mm, and the solution with a double critical point is used as the liquid. 4, the device pop. 3, characterized in that, in order to expand the measuring range, an additional photodetector is inserted into it, and the camera and the body are provided with additional optical windows located perpendicular to the optical axis of the light flux, while the camera is equipped with an additional light guide installed in an additional window and optically coupled with an additional photodetector. Hmph HW d Ц U 01 В 9 L 9 d н Јdd2 MSrn (01-0 S lhll omosh hrttund) bpnpod-d agog g woHvuodu Qugfax / БЗЕЗ1 (& NSHO) Ј I P 01 OS Oh 0 09 OL 08 vo 4 R (omn.edt) i V / Pp 1.5 1.6 1.1 1.8 i, g Fig.E