Strain gauge with impulse overload pressure protection

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to semiconductor strain gauge pressure transducers and can be used in various fields of science and technology related to measuring excess pressure and pressure difference. The pressure strain gauge transducer comprises a measuring silicon membrane with diffusion strain gauges, a silicon support, a silicon membrane with a rigid centre and a silicon pedestal, which are connected to each other by low-melting glass in such a way that they form three cavities connected to each other by chokes. The throttle installed between the measuring cavity, where the measuring diaphragm is installed, and the support cavity, where the diaphragm with a rigid centre is installed, is a planar throttling gap. To achieve this, the rigid centre of the additional silicon membrane is located at a distance of no more than 15 mcm from the lower plane of the support, in the centre of which a hole with a diameter of 5-10 mcm is made. The cross-section of the flow channel of this throttle is not a constant value, but depends on the rate of increase of the overload pressure. When exposed to overload pressure with a steep front, the flow area of the throttle decreases, which means its hydraulic or pneumatic resistance (depending on whether the liquid or gas pressure is being measured) increases, which prevents the overload pressure from reaching the measuring diaphragm.EFFECT: development of a strain gauge transducer with protection against pulse overload pressures.1 cl, 5 dwg

Description

[0001] The invention relates to measuring equipment for recording excess pressure and pressure differences in gaseous and liquid media.

[0002] During emergency operation of pressure sensors, the strain gauge transducer may be exposed to pulsed pressures that exceed the permissible limits by an order of magnitude, resulting in the failure of the transducer. In this case, the transducers used, which have a rather thin membrane (no more than 50 µm thick) (designed to measure pressure differences of a few kPa), can be destroyed by pressure surges reaching several MPa.

[0003] The invention makes it possible to protect a strain gauge from destruction when a pulsed overload pressure is supplied to the strain gauge, the value of which exceeds the permissible value.

[0004] A differential pressure strain gauge transducer is known, which contains a silicon diaphragm with limit stops on both sides of the diaphragm. Under overload pressures, the diaphragm, deflecting in one direction or another, rests on the central projections of the stop elements and stops its deflection. Russian Patent No. 2559300, IPC G01L 9 / 00, G01D 3 / 028, December 24, 2013.

[0005] Membranes' bending stresses remain within the limits at which they rupture. This design protects the strain gauge from slowly changing pressures, but does not fully protect the strain gauge from pulsed overload pressures.

[0006] Another well-known technical solution is a pressure strain gauge transducer, which is a strain gauge with a T-shaped base and is made of several silicon wafers connected using low-melting glass in a vacuum. One of the silicon wafers is a membrane on which strain gauges are diffused. When pressure is applied, the membrane deforms, and the strain gauges convert the membrane voltage into an electrical signal. Russian Federation Patent No. 2169912, IPC G01L 9 / 04, June 27, 2001. This technical solution has been adopted as a prototype.

[0007] A disadvantage of this device is the lack of protection against overload pressure. This is because exposure to overload pressure leads to irreversible deformation of the membrane with strain gauges (which is subject to pressure) or to the destruction of the silicon wafers.

[0008] The proposed invention is aimed at ensuring the operability of the sensor in emergency situations when the sensor is subjected to overload pressures that are an order of magnitude higher than the permissible ones.

[0009] The technical result of the invention is to increase the strength of the strain gauge sensor to the effects of pulsed overload pressures.

[0010] The technical result is achieved by introducing a throttle into the strain gauge transducer, which provides protection against sudden pressure surges due to the fact that its flow area (and consequently, hydraulic or pneumatic resistance - depending on whether the pressure of a liquid or gas is being measured) is not a constant value, but depends on the rate of change of the measured pressure.

[0011] The technical result is achieved in that in a T-shaped pressure strain gauge transducer consisting of a silicon membrane with diffusion strain gauges, which is hermetically connected to a base consisting of a support and a pedestal in such a way that a cavity is formed between the membrane and the base, into which the pressure, the value of which is measured, enters, a pedestal and an additional silicon membrane with a rigid center are introduced, connected on one side to the support, and on the other side - to the pedestal, which is mounted on the pedestal, wherein between the pedestal and the additional membrane with a rigid center, between the additional membrane with a rigid center and the support, and also between the support and the measuring membrane, three cavities are formed, connected to each other by throttle channels, the rigid center of the additional silicon membrane is at a distance of no more than 15 μm from the lower plane of the support, in the center of which an opening with a diameter of 5-10 μm is made.

[0012] The invention is explained by drawings, where:

[0013] 1 - measuring silicon membrane with diffusion strain gauges;

[0014] 2 - measuring cavity between the measuring membrane and the support;

[0015] 3 - support;

[0016] 4 - throttle channel;

[0017] 5 - additional silicon membrane;

[0018] 6 - ​​throttle channel;

[0019] 7 - throttle channel;

[0020] 8 - pedestal;

[0021] 9 - hole for supplying the measured pressure to the receiving chamber;

[0022] 10 - hard center of additional silicon membrane;

[0023] 11 - channel for supplying the measured pressure to the measuring chamber;

[0024] 12 - gap between the rigid center and the support;

[0025] 13 - pedestal;

[0026] 14 - pressure receiving cavity;

[0027] 15 - support cavity.

[0028] Fig. 1 shows the general view of the strain gauge design.

[0029] Fig. 2 shows a section of strain gauge A-A.

[0030] Fig. 3 shows a section of the B-B strain gauge.

[0031] Fig. 4 shows a strain gauge under the influence of pulse overload pressure.

[0032] Fig. 5 shows a throttle installed between the measuring cavity 2 and the support cavity 15 (view “D”).

[0033] The semiconductor pressure strain gauge transducer (Fig. 1) comprises a measuring silicon membrane 1 with diffusion strain gauges, which is hermetically (using low-melting glass) attached to a silicon support 3 in such a way that a measuring cavity (chamber) 2 is formed between the membrane 1 and the support 3, into which the measured pressure is supplied through channel 11. The support 3 is also hermetically connected (using low-melting glass) to an additional silicon membrane 5 with a rigid center 10, wherein a support cavity 15 is formed between the support 3 and the additional silicon membrane 5. The rigid center 10 of the additional silicon membrane 5 is located at a distance h from the lower plane of the support 3 (see Fig. 5), forming a planar throttling gap with a diameter of 2 mm and a thickness h of no more than 15 μm. An additional silicon membrane 5 is hermetically connected (using low-melting glass) to a silicon pedestal 8, which is connected to a silicon pedestal 13.In this case, a pressure receiving cavity 14 is formed between the membrane 5 and the pedestal 8. To supply pressure from the pressure receiving cavity 14 to the measuring cavity 2, throttling channels 4, 6 and 7 are made in the additional silicon membrane 5, and a throttling channel 11 is made in the support 3. To create throttling channels 4 and 7, grooves with a depth of 50 μm and a width of 50 μm are made in heated alkali on the upper and lower planes of the additional silicon membrane 5, as shown in Fig. 1, section C-C. Throttling channels 6 and 11 are created by plasma-chemical etching of the additional silicon membrane 5. The diameter of these throttling channels is 5-10 μm. After assembling the additional silicon membrane 5 with the support 3 and the pedestal 8, throttling holes 4 and 7 of square cross-section are formed, as shown in Fig. 1, section C-C.

[0034] The strain gauge works as follows.

[0035] When measuring static pressure (or slowly changing measured pressure), the pressure through the hole for supplying the measured pressure 9 enters the receiving cavity 14, and through the throttles 4, 6 and 7 enters the support cavity 15. In this case, the same pressure acts on the membrane 5 both from the outside (where the pressure receiving cavity 14 is) and from the inside (from the side of the support cavity 15), therefore the membrane 5 is not deformed, its rigid center 10 does not move, the gap h does not decrease and the measured pressure passes through the planar gap 12 between the rigid center 10 and the lower base of the support 3 into the measuring cavity 2. The pressure in the measuring cavity 2 deforms the measuring membrane 1, the strain gauges of which are also deformed, forming an output electrical signal proportional to the measured pressure.

[0036] When measuring pulse pressure (pressure with a high rate of increase), the pressure, as in the first case, enters the receiving cavity 14, acting on the membrane 5 from the outside. The pressure enters the support cavity 15 through the throttle, consisting of throttling holes 4, 6 and 7. Since the throttle is installed between cavities 14 and 15, the pressure between these cavities cannot be instantly equalized, and on the side of cavity 14 (the outside of membrane 5) the pressure will be greater than in cavity 15. As a result, the membrane 5 will be deformed, as shown in Fig. 4. In this case, the gap h (see Fig. 5) between the rigid center 10 of the membrane 5 and the lower plane of the support 3 with hole 11 (ensuring the supply of pressure to the measuring cavity 2) decreases.As the gap h decreases, the hydraulic (or pneumatic) resistance of the throttle "D" increases. This throttling gap is a planar throttling gap formed by the rigid center 10 of the additional silicon membrane 5 and the support 3. Consequently, the rate of pressure rise in the measuring cavity 2 decreases, thereby protecting the measuring silicon membrane 1 from overload pressure. It should be noted that, under pulsed pressure with a rise time of less than 5-10 ms, the membrane 5 deforms to such an extent that the gap between the rigid center 10 and the support 3 becomes zero, which virtually prevents the overload pressure from entering the support cavity 15 and, consequently, completely protects the measuring membrane 1 from the effects of overload pressure.

[0037] Thus, the proposed design of the strain gauge provides protection against the effects of pulse overload pressures.

Claims

A pressure strain gauge transducer having a T-shape and consisting of a silicon membrane with diffusion strain gauges, which is hermetically connected to a base consisting of a support and a pedestal in such a way that a cavity is formed between the membrane and the base, into which the pressure, the value of which is measured, enters, characterized in that a pedestal and an additional silicon membrane with a rigid center are introduced into the design, connected on one side to the support, and on the other side - to the pedestal, which is mounted on the pedestal, wherein between the pedestal and the additional membrane with a rigid center, between the additional membrane with a rigid center and the support, and also between the support and the measuring membrane, three cavities are formed, interconnected by throttle channels, the rigid center of the additional silicon membrane is at a distance of no more than 15 μm from the lower plane of the support, in the center of which an opening with a diameter of 5-10 μm is made.

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