RU2286555C2 - Strain primary pressure transducer with zero drift compensation and membrane for it - Google Patents

Abstract

FIELD: strain measurement equipment.

SUBSTANCE: the strain primary pressure transducer includes a sapphire monocrystalline membrane having a planar surface and an opposite shaped surface applied to which is the force produced by the pressure to be measured under the action of which the membrane gets deformed, as well as a circuit of resistance strain gauges formed on the membrane planar surface and designed for detection of the applied force on the basis of variation of the resistance of the resistance strain gauges at a deformation of the membrane. The working profile of the membrane shaped surface has the shape of a groove, whose depth is determined by the pressure measurement range. The circuit of resistance strain gauges is preferably oriented to the most strain-sensitive crystallographic directions of the crystalline structure of the membrane. The strain primary pressure transducer may have a lever construction.

EFFECT: compensated zero drift.

14 cl, 4 dwg

Description

FIELD OF THE INVENTION

The present invention relates, in General, to measuring technique and, in particular, to strain-gauge pressure transducers into an electrical signal.

State of the art

Pressure monitoring in various hydraulic and pneumatic systems is extremely important, in particular in the context of safety (for example, to signal an alarming increase in pressure in the system). Typically, pressure control is carried out using various kinds of pressure sensors. The main elements of the pressure sensor are a primary pressure transducer that converts pressure into an electrical signal, secondary signal processing circuits that convert an electrical signal for subsequent output, an output device, and body parts of various designs. One of the main differences between some pressure sensors and others is the accuracy of recording pressure, which depends on the principle of converting pressure into an electrical signal, implemented by the primary pressure transducer. Widely known principles of converting pressure into an electrical signal include strain gauge, piezoresistive, capacitive, inductive, resonant, and ionization.

Currently, the bulk of pressure sensors are manufactured on the basis of strain gauge primary pressure transducers, the principle of which is to measure the strain of strain gauges connected to the circuit formed on a dielectric flat substrate rigidly attached to the membrane. Advantageously, the strain gauge circuit is a strain gauge bridge circuit.

The principle of operation of strain gauge primary pressure transducers is based on the phenomenon of the strain effect in materials. Under the influence of pressure, the membrane is deformed, strain gages due to deformation change their resistance, which leads to imbalance of the bridge. The imbalance linearly depends on the deformation of the resistors and, therefore, on the applied pressure.

From the book "Tensorele. Calculation. Design. Application." B.I. Litvak, Moscow: Mechanical Engineering, 1989, a tensometric pressure transducer 100 is known in which (Fig. 1) strain gauges 110 are formed in an epitaxial silicon film on a sapphire substrate 120 (so called the structure of the SSC (silicon on sapphire)), soldered (for example, by vacuum brazing) 130 to an axisymmetric titanium membrane 140, and strain gauges 110 are connected in a bridge circuit.

The sapphire substrate is a single crystal, while the strain gauge bridge circuit is oriented along the most strain-sensitive crystallographic directions of the substrate structure, which maximizes the sensitivity of the primary pressure transducer. The single-crystal structure of strain gauges and a sapphire substrate, the atomic bonding between them, high dielectric properties and mechanical strength of sapphire provide stability, reliability, and a significant output signal. In addition to sapphire, other materials, such as silicon, can be used to make the substrate.

In the case under consideration, titanium is mainly used as the membrane material, since it has the proper mechanical properties and its coefficient of thermal expansion is close to the coefficient of thermal expansion of sapphire, which minimizes deformations and stresses during heating. The mechanical properties required to ensure certain characteristics of the pressure transducer are imparted precisely to the metal membrane.

Sometimes, instead of silicon strain gages, metal ones are used, for example, copper, nickel, and iron.

As follows from Figs. 1 and 2a, the membrane 140 has a planar surface 210 to which the substrate is soldered, and a profiled surface 220 opposite to it, to which the force exerted by the measured pressure is applied, which, in particular, can correspond to a vacuum. 1 and 2a, the profiled surface of the membrane 140 is depicted as having a working profile in the form of an axisymmetric groove.

The working profile of the profiled surface of the membrane to which the force is applied, in particular, determines its mechanical properties required to ensure predetermined metrological characteristics. For example, in the case of the membrane 140 of FIGS. 1 and 2a with a working profile in the form of a groove, the depth H of the groove is determined by the range of measured pressures and the required metrological characteristics.

Strain gauge pressure transducers may have a lever design. In particular, with reference to FIG. 3, an example of the operation of a membrane-type strain gauge primary pressure transducer as part of a pressure sensor is illustrated. A membrane-type strain gauge primary pressure transducer 4 is placed inside the base 9 in a closed cavity 11 filled with silicon-organic liquid and separated from the medium by corrugated metal membranes 8. The membranes 8 are welded along the outer contour to the base 9 and interconnected by a central rod 6 , which is connected to the end of the lever of the transducer 4 by means of a rod 5. The flanges 10 are sealed with gaskets 3. A positive flange with an open membrane serves for mounting the transducer directly on hnologicheskoy capacity. The influence of the measured pressure causes the deflection of the membranes 8, the bending of the membrane of the strain gauge 4 and the change in resistance of the strain gauges. The electrical signal from the strain gauge is transmitted from the measuring unit to the electronic device 1 via wires through the pressure seal 2.

One of the main disadvantages of the known strain gauge pressure transducers, in particular SPS-based pressure transducers, is the problem of zero drift. With prolonged loads, plastic deformation of the membrane and solder, which has low elastic properties, leads to aging of the solder. As a result, during unloading, there are residual strains (hysteresis phenomenon), which is illustrated in FIG. 4. In particular, measurements show that the residual deflection of the titanium membrane may exceed 10 μm. According to the above, the sapphire substrate has a monocrystalline structure close to ideal, as a result of which its plastic deformation is virtually impossible. As a result, due to the aforementioned residual deformations, the sapphire substrate in the absence of load, however, will be in a stress-strain state in which the resistance of the strain gauges will differ from the value nominally corresponding to the absence of load. This leads to a decrease in the accuracy of recording pressure.

Thus, there is a need for strain gauge pressure transducers to compensate for the above-described zero drift.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a strain gauge pressure transducer with zero drift compensation.

To solve this problem, in accordance with the invention, a tensometric primary pressure transducer and a corresponding membrane of a tensometric primary pressure transducer are provided. According to the invention, the strain gauge primary pressure transducer includes a sapphire single crystal membrane having a planar surface and a profiled surface opposite to it, to which a force is exerted by the measured pressure, under which the membrane is deformed, as well as a strain gauge circuit formed on the plenary surface of the membrane and intended for registration of the applied force based on a change in resistance of strain gages during deformation uu membrane.

According to the invention, the membrane of a tensometric pressure transducer having a planar surface and a profiled surface opposite to it, is entirely made of sapphire and has a single crystal surface.

The strain gauge circuit, which is preferably a bridge circuit formed in an epitaxial silicon film on a planar surface of the membrane, is preferably oriented along the most tensile crystallographic directions of the crystalline structure of the membrane.

It is also preferred that the operating profile of the profiled membrane surface is determined by the mechanical properties of the membrane required to provide predetermined metrological characteristics.

The strain gauge pressure transducer of the present invention may have a lever structure.

List of figures

The above and other features and advantages of the present invention are disclosed in the following description of preferred embodiments thereof, given with reference to the figures in which

Figure 1 is a schematic illustration of a strain gauge pressure transducer corresponding to the prior art.

Fig. 2a is a cross-sectional view of a tensometric pressure transducer according to the prior art.

Fig. 2b is a sectional view of a strain gauge pressure transducer according to the present invention.

FIG. 2 c is a sectional view of a strain gauge primary pressure transducer with metal components in accordance with the present invention.

Figure 3 - an example of the operation of the strain gauge primary pressure transducer membrane-lever type in the pressure sensor.

4 is a graphical illustration of residual deformations.

Description of preferred embodiments of the invention

As noted earlier, the present invention is directed to solving the problem of zero drift in strain gauge pressure transducers.

The present invention proposes the use of a membrane made entirely of sapphire and having a single crystal structure for a strain gauge pressure transducer. In this case, the two components of FIG. 1, namely, the substrate and the membrane, are essentially integrated into one unit {si. Fig.2b). In this case, the strain gauge circuit 110 is placed on the upper planar surface 210 of the membrane corresponding to the present invention, and the lower surface 220 of the membrane in question has a working profile that determines its mechanical properties required to provide predetermined metrological characteristics. In this case, the force generated by the measured pressure is applied to the profiled surface 220 of the sapphire membrane.

In a preferred embodiment of the present invention, the sapphire membrane is axisymmetric, strain gauges deposited, for example, by means of epitaxy, are oriented along the most strain-sensitive crystallographic directions of its crystal structure and combined into a bridge circuit, and the working profile of the lower surface of the membrane has the form of an axisymmetric groove (see Fig.2b ), the depth N of which is determined by the range of measured pressures and the required metrological characteristics. The greater the depth H, the thinner the sapphire layer is under the strain gauge circuit, and therefore, less effort is required to deform the planar surface, which leads to the use of similar strain gauge pressure transducers for a relatively low pressure range.

It should be noted that the complete exclusion of metal components from the design of the strain gauge pressure transducer of the present invention is not implied. In particular, FIG. 2c shows the attachment of a sapphire membrane to a metal base, preferably titanium, in order to impart mechanical precision to the strain gauge pressure transducer. The fastening of the membrane to the base can be performed, for example, by soldering, as shown in Figv. The choice of titanium as the preferred material for the base is due, according to the above, to its mechanical properties, as well as the good consistency of some of its key properties in this context with the corresponding properties of sapphire.

Similarly to the case of FIG. 3 described above, the strain gauge pressure transducer of the present invention may have a lever structure, and its operation is completely similar to that of the pressure transducer 4 of FIG. 3.

The result is the exclusion of the above parasitic effect of the membrane’s plastic deformation and the aging of the solder resulting in it, leading to zero drift, because, in accordance with the foregoing, the sapphire membrane has an essentially perfect single-crystal structure, as a result of which its plastic deformation is virtually eliminated, and the possible presence of metal components and solder, as in the case of Fig.2c, in fact does not affect the strain gauges, since they are sufficiently removed from the planar surface, and due to the pressure measured by the force, causing the deformation of the sapphire membrane, is applied mainly to its profiled surface.

The invention has been disclosed above with reference to specific options for its implementation. For specialists in this field of technology may be obvious and other embodiments of the invention, not changing its essence, as it is disclosed in the present description. Accordingly, the invention should be considered limited in scope only by the following claims.

Claims (14)

1. Strain gauge primary pressure transducer, comprising a membrane having a planar surface and a profiled surface opposite to it, to which a force is applied created by the measured pressure, under the action of which the membrane is deformed, a strain gauge circuit formed on the planar surface of the membrane and designed to record the applied force based on the change in resistance of strain gages when the membrane is deformed, while the membrane is entirely made of sapphire and and has a single-crystal structure, and the working profile of the profiled surface of the membrane has the shape of a groove and is determined by metrological characteristics. 2. The strain gauge primary pressure transducer according to claim 1, in which the strain gauge circuit is oriented along the most strain-sensitive crystallographic directions of the crystal structure of the membrane. 3. The strain gauge pressure transducer according to claim 1, wherein the membrane is axisymmetric. 4. Strain gauge pressure transducer according to claim 3, in which the depth of the groove is determined by the range of measured pressures. 5. The strain gauge primary pressure transducer according to claim 1, wherein the strain gauge circuit is formed in an epitaxial silicon film on a planar membrane surface. 6. The strain gauge primary pressure transducer according to claim 1, in which the strain gauge circuit is a bridge circuit. 7. The strain gauge primary pressure transducer according to claim 1, which has a lever structure. 8. The strain gauge pressure transducer according to claim 1, in which the membrane is attached to a metal base, providing mechanical strength to the design of the strain gauge pressure transducer. 9. The strain gauge primary pressure transducer of claim 8, in which the membrane is attached to the metal base by soldering. 10. The strain gauge primary pressure transducer of claim 8, in which the metal base is made of metal, providing the necessary mechanical properties. 11. The strain gauge primary pressure transducer of claim 10, wherein the metal providing the necessary mechanical properties is titanium. 12. The membrane of the strain gauge primary pressure transducer, which has a planar surface designed to form a strain gauge circuit on it, and a profiled surface opposite to it, to which a force is applied created by the measured pressure, under which the membrane is deformed, while the membrane is entirely made of sapphire and has a single-crystal structure, and the working profile of the profiled membrane surface has the shape of a groove and is determined by metrological requirements their characteristics. 13. The membrane according to item 12, which is axisymmetric. 14. The membrane according to item 13, in which the depth of the groove is determined by the range of measured pressures.

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