A strain gauge liquid level sensor

Abstract

The present invention discloses a strain type liquid level sensor, comprising a housing, a separator, a mounting fixture, an elastic body, a float and four resistance strain gauges. When the liquid level of the container to be measured exceeds the lower end surface of the housing, the liquid flows from the liquid inlet into the lower cavity of the housing; the float in the lower cavity rises under the action of the buoyancy of the liquid, and the elastic body is deformed under the push of the float; the resistance strain gauge senses the deformation of the elastic body and the resistance changes, and the change of resistance is converted into a change of voltage through a Wheatstone bridge, and the liquid level of the container to be measured can be obtained according to the output voltage of the Wheatstone bridge. The present invention measures the liquid level by using the principle that the buoyancy of the float in the liquid changes at different liquid level heights, thereby causing the deformation of the connected elastic body. The sensor has the characteristics of simple structure, high sensitivity, little influence by temperature and the medium to be measured, good anti-interference performance, stable working performance and strong reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a strain type liquid level sensor. Background Art

[0002] With the development of science and technology, liquid level monitoring has spread to all walks of life. Through the monitoring of oil level, various mechanical parts can be lubricated, repaired, mechanical equipment can be cleaned or its normal operation can be ensured in time; in the chemical industry, through the monitoring of each liquid level, the consumption and remaining amount of each chemical product can be sensed in time, so as to replenish raw materials in time. Therefore, liquid level monitoring is particularly important in industrial automation process control. At present, common liquid level sensors include fiber optic sensing liquid level sensors, piezoresistive liquid level sensors and ultrasonic liquid level sensors. Fiber optic sensing liquid level sensors have the advantages of low manufacturing cost and short response time, but their measurement range is limited and their long-term stability is poor. Although the piezoresistive liquid level sensor is low in cost, its sensitivity is low, and its resolution and measurement accuracy are not high. Ultrasonic liquid level sensors can be used for the measurement of liquids and solids, but their reliability is poor, the measurement error is large, and the installation requirements are high. Summary of the invention

[0003] The invention provides a strain type liquid level sensor, which has the characteristics of high sensitivity, good anti-interference, high measurement accuracy and stable working performance.

[0004] To solve the above problems, the present invention is achieved through the following technical solutions:

[0005] A strain type liquid level sensor is composed of a shell, a separator, a mounting fixture, an elastomer, a float and four resistance strain gauges. The shell is a hollow column as a whole. The separator lies across the inner cavity of the shell and divides the inner cavity of the shell into two relatively independent cavities, namely, an upper cavity for the elastomer to be placed and a lower cavity for the float to be placed. A mounting fixture is provided on the upper end surface of the shell, and the mounting fixture is connected to the mounting connector of the container to be tested. At least one through liquid inlet is provided on the lower end surface of the shell. At least one through air hole is provided on the side wall of the shell, and the air hole is located at the upper part of the lower cavity. The elastomer is C-shaped as a whole. Four resistance strain gauges are respectively attached to the inner and outer surfaces of the arc in the middle of the elastomer, of which two pieces of resistance strain gauges are symmetrically distributed on the inner surface of the elastomer, and the other two pieces of resistance strain gauges are symmetrically distributed on the outer surface of the elastomer. The four resistance strain gauges are connected by wires to form a Wheatstone bridge. The elastomer is arranged in the upper cavity of the shell, and the upper end of the elastomer is fixed on the upper end surface of the shell. The float is arranged in the lower cavity of the shell, and the connecting shaft of the upper end of the float passes through the light hole opened in the center of the separator and is connected to the lower end of the elastomer. When the liquid level of the container to be tested exceeds the lower end surface of the shell, the liquid flows into the lower cavity of the shell from the liquid inlet. The float located in the lower cavity rises under the action of the buoyancy of the liquid, the float moves upward, and the elastomer is deformed under the push of the float. The resistance strain gauge senses the change in resistance after the deformation of the elastomer, and converts the change in resistance into a change in voltage through a Wheatstone bridge. The liquid level in the container to be tested can be known according to the output voltage of the Wheatstone bridge.

[0006] In the above solution, the housing is connected together by an upper housing and a lower housing through threaded fitting.

[0007] In the above solution, the air holes are located on the same radial plane of the shell and are distributed radially symmetrically on the side wall of the shell.

[0008] In the above scheme, a strain through hole is opened in the middle of the elastic body.

[0009] Compared with the prior art, the present invention uses the change of buoyancy of the float in the liquid at different liquid levels, thereby causing deformation of the connected elastic body to measure the liquid level. The sensor has the characteristics of simple structure, high sensitivity, small influence by temperature and measured medium, good anti-interference performance, stable working performance and strong reliability. The present invention is suitable for liquid level measurement in various liquid target containers containing oil, lubricating fluid, water, chemical solution, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a structural schematic diagram of a strain type liquid level sensor.

[0011] Figure 2Schematic diagram of the enlarged structure of the elastomer, (a) is the main view, and (b) is the side view.

[0012] Numbers in the figure: 1. shell, 1-1. upper shell, 1-2. lower shell; 2. separator; 3. mounting fixture, 3-1. nut, 3-2. screw; 4. elastomer; 4-1. strain through hole; 5. float; 6. resistance strain gauge; 7. liquid inlet; 8. air vent; 9. external connector. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific examples and with reference to the accompanying drawings. It should be noted that the directional terms mentioned in the examples, such as "upper", "lower", "middle", "left", "right", "front", "back", etc., are only referenced to the directions of the accompanying drawings. Therefore, the directions used are only used for illustration and are not used to limit the scope of protection of the present invention.

[0014] A strain gauge level sensor, such as Figure 1 As shown, it is mainly composed of a housing 1, a separator 2, a mounting fixture 3, an elastic body 4, a float 5 and a resistance strain gauge 6.

[0015] The housing 1 is a hollow columnar body, and is connected by an upper housing 1-1 and a lower housing 1-2 through threaded engagement. A mounting hole for a screw 3-2 is provided at the center of the upper end surface of the upper housing 1-1, and a thread is provided at the inner edge of the mounting hole. At least one through-going liquid inlet 7 is provided at the lower end surface of the lower housing 1-2. In a preferred embodiment of the present invention, the number of the liquid inlet 7 is one.

[0016] The separator 2 is in the form of a sheet, and a light hole is provided in the center thereof. The separator 2 is horizontally installed in the inner cavity of the outer shell 1, and divides the inner cavity of the outer shell 1 into two relatively independent cavities, namely, an upper cavity for placing the elastomer 4 and a lower cavity for placing the float 5. In a preferred embodiment of the present invention, the separator 2 is located at the junction of the upper outer shell 1-1 and the lower outer shell 1-2, and is installed at the lower part of the upper outer shell 1-1. The outer edge of the separator 2 is threaded, and the inner wall of the upper outer shell 1-1 is tapped with threads, and the screw on the outer edge of the separator 2 matches the upper thread on the inner wall of the upper outer shell 1-1. At least one air vent 8 is provided on the side wall of the outer shell 1, and the air vent 8 is located at the upper part of the lower cavity of the outer shell 1, and is located above the maximum height of the measurement range of the sensor. In a preferred embodiment of the present invention, there are two air holes 8, which are located on the same radial plane of the lower shell 1-2 and are radially symmetrically distributed on the side wall of the lower shell 1-2 to ensure that the pressure inside and outside the shell 1 is consistent, so that the liquid level inside and outside the cavity is consistent, ensuring the accuracy of the measurement. When the liquid level of the measured liquid changes, in order to keep the liquid level inside and outside consistent, the gas in the inner cavity of the shell 1 is discharged through the air holes 8 or the gas is sucked into the inner cavity of the shell 1 to keep the atmospheric pressure inside and outside the inner cavity of the shell 1 consistent.

[0017] The mounting fixture 3 includes a nut 3-1 and a screw 3-2. The screw 3-2 is in an inverted T shape, and the upper end of the screw 3-2 passes through the mounting hole at the upper end of the upper shell 1-1, and the thread of the outer wall of the screw 3-2 matches the thread of the inner wall of the mounting hole. The nut 3-1 is sleeved on the upper end of the screw 3-2, and the inner thread of the nut 3-1 matches the outer thread of the screw 3-2. The sensor is installed on the external connector 9 of the external container to be tested through the mounting fixture 3. The external connector 9 is a component installed on the container to be tested or other parts for fixing the liquid level sensor of the present invention. Its structural form has nothing to do with the present invention, as long as the mounting fixture 3 of the present invention can be installed.

[0018] Elastomer 4 Figure 2As shown, the whole is C-shaped. A strain through hole 4-1 is opened in the middle of the elastic body 4. The purpose of opening the strain zone on the elastic body 4 is that when the elastic body 4 receives upward pressure or downward tension, stress concentration is formed around the hole, so the strain caused is the largest, so that the output of the sensor is more sensitive. The strain zone of the elastic body 4 is on both sides of the strain through hole 4-1 on the arc of the elastic body 4. The resistance strain gauge 6 is attached to the strain zone of the inner and outer surfaces of the middle arc of the elastic body 4. In the preferred embodiment of the present invention, there are 4 resistance strain gauges 6. Two of them are attached to the inner surface of the elastic body 4 and are symmetrically arranged above and below the strain through hole 4-1; the other two are attached to the outer surface of the elastic body 4 and are symmetrically arranged above and below the strain through hole 4-1. The 4 resistance strain gauges 6 are connected by wires to form a Wheatstone bridge, and are respectively arranged on the relative bridge arms of the Wheatstone bridge.

[0019] The elastic body 4 is arranged in the upper cavity of the housing 1, and the upper end of the elastic body 4 is mounted on the screw 3-2 of the upper housing 1-1 by screws. The float 5 is arranged in the lower cavity of the housing 1, and the connecting shaft of the upper end of the float 5 passes through the optical hole in the center of the separator 2 and is connected to the lower end of the elastic body 4. The external liquid enters the cavity from the liquid inlet hole at the bottom of the lower housing 1-2, so that even if disturbances are generated externally due to various reasons, causing the liquid level to fluctuate, the external fluctuations will not be transmitted to the cavity, so that the buoyancy of the float 5 located in the cavity will not be affected by the external disturbances, thereby ensuring the stable output of the sensor.

[0020] When the liquid level of the liquid to be detected exceeds the lower end surface of the housing 1, the liquid flows into the lower cavity of the housing 1 from the liquid inlet 7 at the bottom of the lower housing 1-2. The liquid level in the lower housing 1-2 rises, and the float 5 located in the lower cavity rises under the action of the buoyancy of the liquid. The float 5 moves upward and transmits force to the elastic body 4. The elastic body 4 is deformed under the push of the float 5. The resistance strain gauge 6 senses the change in resistance of the elastic body 4 after the deformation, and converts the change in resistance into a change in voltage through the Wheatstone bridge. The buoyancy and liquid level can be inferred based on the output voltage of the bridge.

[0021] Assume that the volume of the float 5 immersed in the liquid is V:

[0022] V=πr 2 h ①

[0023] In the formula, r represents the radius of the float 5, and h represents the height of the float immersed in the liquid.

[0024] The buoyancy F of float 5 is:

[0025] F=ρgV ②

[0026] Where ρ represents the oil density and g represents the gravitational acceleration constant.

[0027] The bending moment M on the elastic body 4 is:

[0028] M=F(L+R) ③

[0029] In the formula, L represents the distance from the point of force application to the center of the circle, and R represents the radius of the arc.

[0030] The strain ε of the elastic body 4 is m :

[0031]

[0032] In the formula, E is the elastic modulus of the elastic body 4, a is the thickness of the arc-shaped elastic body 4, and b is the width of the arc-shaped elastic body 4.

[0033] For the bridge output voltage u:

[0034] u=Ukε m ⑤

[0035] In the formula, k is the sensitivity coefficient, and U is the bridge supply voltage. From the above, it can be seen that the output voltage u is proportional to the liquid level h.

[0036] According to equations ① to ⑤, the sensor parameters are designed and the optimal sensitivity can be obtained by controlling the values ​​of each parameter within a reasonable range.

[0037] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A strain gauge liquid level sensor, characterized in that: It is composed of a housing (1), a separator (2), a mounting fixture (3), an elastic body (4), a float (5) and four resistance strain gauges (6); The outer shell (1) is a hollow columnar body; the partition sheet (2) lies across the inner cavity of the outer shell (1) and divides the inner cavity of the outer shell (1) into two relatively independent cavities, namely, an upper cavity for accommodating the elastic body (4) and a lower cavity for accommodating the float (5); The upper end surface of the housing (1) is provided with a mounting fixture (3), and the mounting fixture (3) is connected to the mounting connector of the container to be measured; the lower end surface of the housing (1) is provided with at least one through-going liquid inlet (7); the side wall of the housing (1) is provided with at least one through-going air hole (8), and the air hole (8) is located at the upper part of the lower cavity and above the maximum height of the measuring range of the sensor; when the liquid level of the measured liquid changes, the gas in the inner cavity of the housing (1) is discharged through the air hole (8) or the gas is sucked into the inner cavity of the housing (1), so as to keep the atmospheric pressure inside and outside the inner cavity of the housing (1) consistent; The elastic body (4) is in a C-shape as a whole; four resistance strain gauges (6) are respectively attached to the inner and outer surfaces of the arc in the middle of the elastic body (4), wherein two resistance strain gauges (6) are symmetrically distributed on the inner surface of the elastic body (4) and the other two resistance strain gauges (6) are symmetrically distributed on the outer surface of the elastic body (4); the four resistance strain gauges (6) are connected by wires to form a Wheatstone bridge; The elastic body (4) is arranged in the upper cavity of the housing (1), and the upper end of the elastic body (4) is fixed to the upper end surface of the housing (1); the float (5) is arranged in the lower cavity of the housing (1), and the connecting shaft of the upper end of the float (5) passes through the light hole opened in the center of the partition plate (2) and is connected to the lower end of the elastic body (4); When the liquid level in the container to be tested exceeds the lower end surface of the housing (1), the liquid flows from the liquid inlet (7) into the lower cavity of the housing (1); the float (5) located in the lower cavity rises under the action of the buoyancy of the liquid, the float (5) moves upward, and the elastic body (4) is deformed under the push of the float (5); the resistance strain gauge (6) senses the change in resistance of the elastic body (4) after the deformation, and converts the change in resistance into a change in voltage through a Wheatstone bridge, and the liquid level height in the container to be tested can be obtained according to the output voltage of the Wheatstone bridge; wherein the output voltage u is proportional to the liquid level height h, that is: In the formula, u represents the output voltage of the bridge, h represents the height of the immersion in the liquid, U represents the power supply voltage of the bridge, k represents the sensitivity coefficient, ρ represents the oil density, g represents the gravity acceleration constant, r represents the radius of the float, L represents the distance from the point of application of the force of the elastic body to the center of the circle, R represents the arc radius of the elastic body, E is the elastic modulus of the elastic body, a is the thickness of the arc elastic body, and b is the width of the arc elastic body.

2. A strain gauge liquid level sensor according to claim 1, characterized in that: The housing (1) is composed of an upper housing (1-1) and a lower housing (1-2) connected together by threaded engagement.

3. A strain gauge liquid level sensor according to claim 1, characterized in that: The air holes (8) are located on the same radial plane of the outer shell (1) and are distributed radially symmetrically on the side wall of the outer shell (1).

4. A strain gauge liquid level sensor according to claim 1, characterized in that: A strain through hole (4-1) is opened in the middle of the elastic body (4).

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