Tension sensor measuring circuit, tensiometer and calculation method

Abstract

The invention belongs to the technical field of underground tension measurement, and particularly relates to a tension sensor measuring circuit, a tensiometer and a calculation method. The measuring circuit comprises four groups of strain units, the four groups of strain units are sequentially connected to form a full-bridge circuit, and the strain units on opposite bridge arms of the full-bridge circuit are a first strain unit and a second strain unit respectively; the two first strain units are used for sensing axial strain; each second strain unit comprises at least two strain gauges which are connected in series, at least one strain gauge is obliquely arranged to form a certain included angle with the axial direction and is used for sensing circumferential strain, the other strain gauges are suspended, and the included angle is used for enabling the signal variation of the adjacent first strain unit and second strain unit to be the same. The problem that tension measurement is complex and high in cost is solved, the complex mechanical compensation problem is converted into circuit configuration through source compensation design, and therefore comprehensive optimization is achieved in multiple dimensions such as the structure, reliability, cost, performance and maintainability, and the method is suitable for petroleum logging scenes with strict requirements.

Description

Technical Field

[0001] This invention belongs to the field of downhole tension measurement technology, specifically relating to a tension sensor measurement circuit, a tension meter, and a calculation method. Background Technology

[0002] In oil well logging operations, real-time and accurate measurement of the axial force (tension) borne by the downhole instrument string is crucial for monitoring operational safety, determining instrument sticking conditions, and optimizing operating parameters. The axial force on the logging instrument downhole consists of two parts: one is a force component (Fp) proportional to the downhole ambient pressure, and the other is a force component (Fz) that primarily reflects cable or drill pipe traction, instrument weight, buoyancy, and friction, and is independent of ambient pressure. The latter (Fz) is key information required for operational monitoring.

[0003] Currently, the mainstream technical solution for downhole tension measurement is to integrate a dedicated tension meter into the instrument string, and indirectly calculate the axial force by measuring the strain generated in that section when it is subjected to force.

[0004] However, the ambient pressure P not only generates an additional axial force component Fp, but also induces surface strain (including circumferential strain εhp and axial strain εzp) on the measuring section shell. These strains caused by pure pressure (especially εzp) are mixed into the final strain measurement signal, causing the measured "apparent tension" to deviate significantly from the true target tension Fz.

[0005] To eliminate the influence of environmental pressure P, a hydraulic thrust mechanism that generates a force equal in magnitude but opposite in direction to Fp is typically designed to actively counteract the axial force caused by the pressure. However, this method has drawbacks: it introduces complex moving mechanisms and hydraulic circuits such as precision pistons, cylinder liners, and seals, which significantly increases the structural complexity and manufacturing cost of the tension meter.

[0006] Alternatively, a dual-structure compensation method can be used, separating the force and pressure paths: designing mutually isolated axial force-bearing bodies (force transmission shafts) and pressure-sensitive bodies, and attaching strain gauges to each for measurement, using the output of the pressure-sensitive body to compensate for the signal of the main force-bearing body. However, this method has drawbacks: it requires designing two independent mechanical structures and precisely coupling them, resulting in complex structures and large volumes; the matching and compensation algorithms between the two signals are easily affected by factors such as temperature and creep, making it difficult to guarantee long-term stability and compensation accuracy.

[0007] Alternatively, an external pressure sensor can be used for pressure compensation: an additional independent pressure sensor is installed to measure the ambient pressure P, and then Fp is subtracted by calculation. However, this method has drawbacks: it increases the number of system components, wiring, and cost; it requires ensuring the synchronization and positional consistency of tension and pressure measurements, resulting in high system integration complexity; and a failure of the pressure sensor itself can directly lead to the failure of the entire tension measurement system. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this paper provides a tension sensor measurement circuit, a tension meter, and a calculation method to solve the problems of complex and costly tension measurement.

[0009] On the one hand, the technical solution of the present invention to solve the above-mentioned technical problems is as follows: a tension sensor measurement circuit, which includes four sets of strain units, the four sets of strain units are connected in sequence to form a full bridge circuit, and the strain units on the opposite arms of the full bridge circuit are respectively the first strain unit and the second strain unit;

[0010] The first strain unit is used to sense axial strain;

[0011] The second strain unit includes at least two strain gauges connected in series. At least one of the strain gauges is inclined at a certain angle to the axial direction to sense circumferential strain. The remaining strain gauges are suspended. The angle is used to ensure that the signal changes of adjacent first and second strain units are the same, so as to maintain bridge balance and eliminate signal interference.

[0012] Based on the above technical solution, the embodiments of this application can be further improved as follows:

[0013] In this embodiment, since it is used in well logging, the axial direction is the vertical Z-axis.

[0014] In one embodiment, the first strain unit includes a number of strain gauges connected in series, equal to the number in the second strain unit, and a plurality of the strain gauges in the first strain unit are arranged parallel to the axial direction.

[0015] In one embodiment, the number of strain gauges included in the strain unit is set to n, and the number of strain gauges n and the included angle θ satisfy the following formula when the bridge is balanced:

[0016] ;

[0017] Where R0 is the resistance value of the strain gauge, K0 is the sensitivity coefficient of the strain gauge, εzp is the axial strain of the strain gauge under pressure P, εhp is the circumferential strain of the strain gauge under pressure P, and Kp is the ratio of the circumferential strain εhp to the axial strain εzp of the strain gauge when Poisson's ratio is υ.

[0018] Secondly, this embodiment also discloses a tension meter, which includes:

[0019] A cylindrical body, wherein a measuring section with a thickness smaller than that at both ends is formed in the middle of the cylindrical body;

[0020] The core frame is fitted into the measuring section inside the cylinder. A flexible printed circuit board is provided on the surface of the core frame, and the measuring circuit as described above is provided on the flexible printed circuit board. The first strain unit and the second strain unit are arranged symmetrically and alternately in the circumferential direction. The strain gauges in the first strain unit and the strain gauges in the second strain unit are inclined and disposed on the surface of the core frame. The remaining strain gauges in the second strain unit are suspended in the air above the core frame.

[0021] In one embodiment, the core frame includes a first tube frame and a second tube frame that are nested together. The flexible printed circuit board is disposed in the first tube frame on the inner side. The two ends of the tube frame are folded outward to form end edges. The inner wall of the cylinder forms a step that abuts against the end edges.

[0022] In one embodiment, the system further includes joints that are sealed to both ends of the cylinder, and a protective sleeve that is fitted over the outside of the cylinder is provided between the two joints.

[0023] In one embodiment, a temperature sensor disposed on the flexible printed circuit board is also included.

[0024] Finally, this embodiment also discloses a calculation method for calculating the angle of the strain gauges tilted in the second strain unit as described above. The calculation method includes:

[0025] The static resistances of the two first strain gauges and the two second strain gauges are set to Ra, Rd, Rb and Rc respectively, where the resistance of the strain gauge is set to R0 and the sensitivity is set to K0.

[0026] After applying environmental pressure P, the change in resistance of Ra is obtained. and the change in resistance of Rb ;

[0027] When ΔRa = ΔRb, the bridge is balanced. Substituting... get: ;

[0028] To obtain the relationship between the angle θ of the tilted strain gauge and the number of strain gauges n: .

[0029] Furthermore, it also includes calculating the formula based on the bridge output signal after applying the instrument tension F. Therefore, based on the output signal Uab of the full-bridge circuit, the target axial force can be calculated. .

[0030] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0031] 1. The structure is highly simplified, significantly improving reliability. This invention abandons compensation mechanisms with numerous complex components, such as external hydraulic pressure sensors. Instead, it directly utilizes the deformation characteristics of the pressure-bearing measurement section under pressure (i.e., the circumferential strain and axial strain are in a fixed ratio). Through the directional arrangement of strain gauges and the ingenious configuration of the bridge circuit, self-compensation for the influence of environmental pressure is achieved at the circuit signal level. The entire measurement system consists only of a pressure-bearing shell, strain gauges adhered to its inner wall, and supporting circuitry, without any moving parts or complex force transmission paths. This simplified structure directly reduces potential failure points (such as seal failure and component jamming), resulting in higher long-term operational reliability of the tension gauge in harsh downhole environments with high temperature, high pressure, and strong vibration.

[0032] 2. Manufacturing and maintenance costs are significantly reduced. Using standard strain gauges eliminates the need for customized sensitive elements with special sensitivity, resulting in low procurement costs and a stable supply. This not only reduces the difficulty and time costs of manual pasting and wiring but also ensures consistent and accurate installation, improving production efficiency and product quality consistency, thereby reducing overall manufacturing and maintenance costs.

[0033] 3. High pressure compensation accuracy and good temperature stability. The compensation principle is based on the inherent and definite elastic mechanical relationship of the pressure-bearing tubing string. All working strain gauges have completely identical parameters and temperature characteristics. Furthermore, the non-stressed matching resistors also participate in the bridge circuit, providing a natural and excellent temperature self-compensation effect. The tilt angle θ and the number of series gauges n can be precisely designed according to theoretical formulas, ensuring that the pressure compensation reaches a high degree of balance in the initial state. This compensation method, based on the intrinsic properties of materials and circuit symmetry, offers far superior accuracy and long-term stability compared to mechanical compensation methods that rely on multi-component cooperation.

[0034] 4. Easy installation, maintenance, and replacement: Multiple strain gauges and their connecting circuits are prefabricated into a single integrated component using a flexible printed circuit board. With the assistance of a core frame equipped with positioning capabilities, all measuring elements can be quickly and accurately positioned at designated locations on the inner wall of the measuring section in one go. This design greatly simplifies on-site installation and subsequent maintenance: if a measuring component is damaged, only the entire flexible circuit board module needs to be replaced, eliminating the need for meticulous cleaning and re-attaching of the inner wall, significantly improving maintenance convenience.

[0035] 5. The output signal directly reflects the target axial force, simplifying system integration. The output bridge signal (Uab) directly and linearly corresponds to the axial force Fz that needs to be measured and is independent of environmental pressure. The influence of environmental pressure is eliminated at the sensor front end, eliminating the need for additional pressure signal acquisition, calibration, and complex subtraction operations in the back-end signal processing system. This simplifies the design of the signal conditioning circuit and data processing software for the entire logging instrument string, reducing system integration complexity. This invention, through a source compensation design concept, transforms the complex mechanical compensation problem into a sophisticated circuit configuration problem, thereby achieving comprehensive optimization in multiple dimensions such as structure, reliability, cost, performance, and maintainability. It is particularly suitable for high-temperature and high-pressure applications in oil logging where reliability and cost are stringent requirements. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 The circuit diagram when each bridge arm consists of two strain gauges connected in series;

[0038] Figure 2 The circuit diagram when each bridge arm consists of 3 strain gauges connected in series;

[0039] Figure 3 The circuit diagram when each bridge arm consists of 4 strain gauges connected in series;

[0040] Figure 4 A simplified diagram of the installation of the strain gauge on the inner wall of the tension meter;

[0041] Figure 5 , corresponding to Figure 2 Simplified assembly diagram of the configured tension gauge;

[0042] Figure 6 Schematic diagram of strain gauge dimensions;

[0043] Figure 7 Schematic diagram of strain gauge installation at an angle.

[0044] Figure label:

[0045] 1-Upper connector, 2-Cylinder, 3-Lower connector, 4-Protective sleeve, 5-First tube rack, 6-Second tube rack, 2e-Flexible printed circuit board, 2f-Solder point, 2g-Lead wire, 2h-Temperature sensor. Detailed Implementation

[0046] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0047] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0048] In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0049] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0050] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0051] Example 1

[0052] The present invention provides a tension sensor measurement circuit, which includes four sets of strain units. The four sets of strain units are connected in sequence to form a full-bridge circuit. The strain units on the opposite arms of the full-bridge circuit are respectively a first strain unit and a second strain unit, that is, two first strain units and two second strain units are connected in sequence in an alternating manner to form a full-bridge circuit.

[0053] The first strain unit is used to sense axial strain; the second strain unit is used to sense circumferential strain, and includes at least two strain gauges connected in series. At least one strain gauge is inclined at a certain angle to the axial direction to sense circumferential strain, and the remaining strain gauges are suspended to achieve resistance matching and temperature compensation. The angle is used to make the signal change of adjacent first strain units and second strain units the same to maintain bridge balance and eliminate interference.

[0054] Specifically, the first strain unit includes a number of strain gauges connected in series, equal to the number in the second strain unit, and a plurality of strain gauges in the first strain unit are arranged parallel to the axial direction.

[0055] In this embodiment, the first strain unit and the second strain unit are the four bridge arms Ra, Rb, Rc, and Rd for measuring resistance, respectively. The first strain unit corresponds to Rb and Rc, and the second strain unit corresponds to Ra and Rd. The bridge arm (Rb and Rc) of the first strain unit used to sense the axial force is composed of n (n≥2) strain gauges connected in series. The sensing directions of these strain gauges are all strictly parallel to the axial direction. In this embodiment, since it is used in well logging, the axial direction is the vertical Z-axis direction.

[0056] The second strain unit, used for sensing circumferential strain and performing pressure compensation, also consists of n identical strain gauges connected in series, but with a different connection method: in this series combination, only one strain gauge (denoted as Ra1, Rd1) is actually attached to the inner wall of the measuring section and senses strain, and its sensing direction forms a specific tilt angle θ with the Z-axis; the remaining (n-1) strain gauges in this series combination act as "suspended" matching resistors, not attached to the stressed body, and therefore do not sense any mechanical strain, but are only used for electrical resistance matching and temperature compensation. Figure 6 As shown, the strain gauge has a length of L, a width of B, and a thickness of t. The lead wire 2g is omitted and not drawn. The arrow points in the direction of the sensitive strain. Figure 7 As shown, when the strain gauge is installed at an angle θ to the Z-axis, it will simultaneously sense the strain εz in the Z-axis direction and the circumferential strain εh perpendicular to the Z-axis, and its impedance change will be output. The theoretical basis of structural mechanics is as follows: the tension gauge measuring section is a thick-walled tube. When subjected to external pressure, its circumferential strain εhp and axial strain εzp change linearly with the external pressure P in a range far from the elastic limit. The following relationship exists between them:

[0057] ;

[0058] Where υ is the Poisson's ratio of the material. For example, when υ=0.3, Kp =4.25; when υ=0.305, Kp =4.3462.

[0059] The number of strain gauges included in the strain unit is set to n. When the bridge is balanced, the number of strain gauges n and the included angle θ satisfy the following formula:

[0060] ;

[0061] Where R0 is the resistance value of the strain gauge, K0 is the sensitivity coefficient of the strain gauge, εzp is the axial strain of the strain gauge under pressure P, εhp is the circumferential strain of the strain gauge under pressure P, and Kp is the ratio of the circumferential strain εhp to the axial strain εzp of the strain gauge when Poisson's ratio is 0.3.

[0062] Specifically, the design of the tilt angle θ is crucial for achieving bridge balance. The following balance condition must be met: Under pure external pressure P, the change in resistance generated by a single tilted strain gauge (sensitive to εzp and εhp), where εhp is the circumferential strain and εzp is the axial strain, is equal to the total change in resistance generated by n axially mounted strain gauges (all sensitive to εzp).

[0063] Get Substitute The solution is: .because Substituting into it, we can get Therefore, for a selected number of series plates n, a unique tilt angle θ can be calculated, so that the pressure effect is precisely canceled out.

[0064] like Figure 1 As shown, when each bridge arm consists of two strain gauges connected in series (n=2), the calculated tilt angle θ is approximately 13.69°. Rb and Rc each consist of two strain gauges connected in series, parallel to the Z-axis, symmetrically installed, and sensitive to axial strain εz; Ra and Rd each consist of two strain gauges connected in series, with Ra1 and Rd1 tilted and symmetrically installed, simultaneously sensitive to strain in two directions, while Ra2 and Rd2 are suspended as matching resistors.

[0065] like Figure 2 As shown, when each bridge arm consists of 3 strain gauges connected in series (n=3), the calculated tilt angle θ is approximately 29.32°. Rb and Rc each consist of 3 strain gauges connected in series, parallel to the Z-axis, and symmetrically installed in the circumferential direction to sense the axial strain εz; Ra and Rd each consist of 3 strain gauges connected in series, with Ra1 and Rd1 installed at an angle to sense strain in both directions simultaneously, and Ra2, Ra3 and Rd2, Rd3 suspended as matching resistors.

[0066] like Figure 3As shown, when each bridge arm consists of 4 strain gauges connected in series (n=4), the calculated tilt angle θ is approximately 50.80°. Rb and Rc each consist of 4 strain gauges connected in series, parallel to the Z-axis, and symmetrically installed in the circumferential direction to sense the axial strain εz; Ra and Rd each consist of 4 strain gauges connected in series, with Ra1 and Rd1 installed at an angle to sense strain in both directions simultaneously. Ra2, Ra3, Ra4 and Rd2, Rd3, Rd4 are suspended as matching resistors (not under load).

[0067] Example 2

[0068] This embodiment also discloses a tension meter, which includes: a cylinder 2, a core frame, and the measuring circuit in embodiment 1.

[0069] like Figure 4 and 5 As shown, a measuring section with a thickness smaller than that at both ends is formed in the middle of the cylinder 2. Strain is generated through the measuring section and transmitted to the measuring circuit. The core frame is matched and snapped into the measuring section inside the cylinder 2. A flexible printed circuit board 2e is provided on the surface of the core frame. The measuring circuit as described above is provided on the flexible printed circuit board 2e. The first strain unit and the second strain unit are arranged symmetrically and alternately in the circumferential direction. The strain gauges in the first strain unit and the strain gauges in the second strain unit that are inclined are provided on the surface of the core frame. The remaining strain gauges in the second strain unit are suspended in the air above the core frame.

[0070] By employing a flexible printed circuit board 2e, all required strain gauges, including those axially mounted, tilted mounted, and those suspended as matching resistors, are integrated onto the flexible printed circuit board 2e using surface mounting or direct etching. Electrical connections between the strain gauges are achieved through wiring on the flexible circuit board.

[0071] Specifically, the flexible printed circuit board 2e is wound and adhered to the outer surface of a tubular core frame. During adhesion, it is necessary to ensure that the strain gauge areas designed to be "suspended" are not coated with adhesive or remain unbonded to the core frame surface, thus ensuring they are truly mechanically "suspended." The core frame, along with the flexible circuit board on it, is then inserted into the inner cavity of the tension gauge measuring section. The solder joints 2f on the flexible circuit board are used to lead out the bridge signal via lead wires 2g.

[0072] To achieve axial positioning and fixation of the core frame, the core frame includes a first tube frame 5 and a second tube frame 6 that are nested together. The flexible printed circuit board 2e is disposed in the first tube frame 5 on the inner side. Axial positioning and fixation are achieved by the cooperation of the two tube frames. Specifically, the two ends of the tube frame are folded outward to form end edges, and the inner wall of the cylinder 2 forms a step that abuts against the end edges, thus achieving positioning and fixation.

[0073] It also includes joints that are sealed to both ends of the cylinder 2, namely upper joint 1 and lower joint 3. The cylinder 2 in the tension gauge is sealed to both joints. A protective sleeve 4 is provided between the two joints and is fitted to the outside of the cylinder 2 to withstand the environmental pressure. Its interior is generally at normal pressure (P0≈0), and the pressure difference between the inside and outside is P.

[0074] like Figure 4 As shown, axial length dimension A is the connection and transition section, dimension B is the measuring section, and dimension C is the connection and transition section. D1 is the outer diameter of the measuring section tubing, D2 is the inner diameter of the measuring section tubing, D3 is the maximum outer diameter of the tension gauge housing, and D4 is the outer diameter of the instrument on which the tension gauge is installed. D1 and D2 are dimensions that determine the characteristics of the tension gauge, while dimensions D3, D4, and the tool interface belong to the structural design and installation adaptation design.

[0075] It also includes a temperature sensor 2h disposed on the flexible printed circuit board 2e, used to monitor the temperature of the strain gauge area in order to perform temperature compensation on the measurement signal and further improve the accuracy.

[0076] Example 3

[0077] This embodiment also discloses a calculation method for calculating the angle of the strain gauges that are inclined in the second strain unit as described above.

[0078] Since the circumferential strain of the tension gauge is significantly higher than the axial strain under external pressure P, the amplitude of the response signal to the axial strain can be increased by using multiple strain gauges installed in the same direction and connected in series, and the amplitude is proportional to the number of strain gauges connected in series.

[0079] By tilting the strain gauges sensitive to circumferential strain, the response amplitude to circumferential strain can be reduced, and its projection component in the strain gauge's sensitive direction can be made equal. Constructing adjacent bridge arms of the measurement bridge circuit, appropriately determining the number of series-connected gauges, and appropriately determining the tilt angle can precisely ensure that the output signals generated by the external pressure P in adjacent bridge arms are equal, maintaining bridge balance and eliminating the influence of external pressure P on the output signal.

[0080] Specifically, the calculation method includes:

[0081] The static resistances of the two first strain gauges and the two second strain gauges are set to Ra, Rd, Rb and Rc respectively, where the resistance of the strain gauge is set to R0 and the sensitivity is set to K0.

[0082] When strain units Rb and Rc are each composed of two strain gauges connected in series, with the sensitive direction parallel to the Z-axis and symmetrically installed in the circumferential direction, the sensitive axial strain εz is measured.

[0083] Each strain gauge, Ra and Rd, consists of two strain gauges connected in series. Ra1 and Rd1 are installed at an angle and symmetrically, simultaneously sensing strain in two directions. Ra2 and Rd2 are suspended as matching resistors and are not sensitive to any strain. The angled strain gauges are drawn at an angle in the figure; the suspended strain gauges used as matching resistors are represented by dashed lines.

[0084] In addition, it can also be like Figure 2 , 3 As shown, each bridge arm uses more strain gauges. Figure 2 Each bridge arm uses three resistors: Rb and Rc are connected in series to sense axial strain. Ra and Rd each use one resistor installed at an angle to sense strain in two directions, while the others are left suspended as matching resistors. Figure 3 Each bridge arm uses four resistors, with Rb and Rc connected in series to sense the axial strain. Ra and Rd each use one resistor installed at an angle to sense the strain in both directions, while the others are left suspended as matching resistors.

[0085] Where Ra is composed of n identical strain gauges connected in series, with a corresponding resistance R0 and sensitivity k0, then the initial resistance of this strain element is... .

[0086] If the initial resistances are all equal (R0), the sensitivity coefficients are all the same (K0), and the material Poisson's ratio is 0.305, the specific characteristic parameters of each bridge arm are as follows:

[0087] After applying environmental pressure P, only one tilted strain gauge (Ra1, Rd1) in each of the generated εhp, εzp, Ra, and Rd is sensitive to strain in both directions:

[0088] Resistance change of the Ra strain gauge assembly ;

[0089] Resistance change of the Rb strain gauge assembly ;

[0090] Resistance change of the Rc strain gauge assembly ;

[0091] Resistance change of the Rd strain gauge assembly ;

[0092] When ΔRa = ΔRb and ΔRc = ΔRd, the bridge is balanced, eliminating the influence of pressure P on the output signal. Therefore, the balance condition can be obtained:

[0093] ;

[0094] The simplified relationship between the angle θ of the tilted strain gauge and the number of strain gauges n can be obtained as follows: ;

[0095] Therefore, it can be obtained that...

[0096] for Figure 1 When n=2, the tilt angle θ=13.69°;

[0097] for Figure 2 When n=3, the tilt angle θ=29.32°;

[0098] for Figure 3 When n=4, the tilt angle θ=50.8°;

[0099] Furthermore, after applying the instrument tension F, the strain gauges connected in series in Rb and Rc are sensitive to the axial strain εzf caused by Fz; while in Ra and Rd, only one strain gauge senses the strains εzf and εzh in both directions.

[0100] At this point, the change in resistance of the Ra strain gauge assembly is:

[0101] ;

[0102] ;

[0103] ;

[0104] Resistance change of the Rb strain gauge assembly ;

[0105] Resistance change of the Rc strain gauge assembly ;

[0106] Resistance change of the Rd strain gauge assembly ;

[0107] According to the formula for calculating the output signal of the bridge After substituting the changes in resistance,

[0108] ;

[0109] Simplified, we can obtain ;

[0110] Therefore, we can obtain:

[0111] for Figure 1 Each bridge arm has two strain gauges, n=2, θ=13.69. ;

[0112] for Figure 2 Each bridge arm has 3 strain gauges, n=3, θ=29.32. ;

[0113] for Figure 3 Each bridge arm has 4 strain gauges, n=4, θ=50.80. ;

[0114] Therefore, the calculation formulas for axial strain εz, axial stress σzf, and axial force Fz can be obtained based on the measured output signal Uab:

[0115] ;

[0116] ;

[0117] ;

[0118] ;

[0119] ;

[0120] Finally, the target axial force was calculated. ;

[0121] Referring to the attached diagram, we can obtain:

[0122] like Figure 1 Each bridge arm has two strain gauges, n=2, θ=13.69. ;

[0123] like Figure 2 Each bridge arm has 3 strain gauges, n=3, θ=29.32.

[0124] like Figure 3 Each bridge arm has 4 strain gauges, n=4, θ=50.80. .

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tension sensor measurement circuit, characterized in that, It includes four sets of strain units, which are connected in sequence to form a full-bridge circuit. The strain units on the opposite arms of the full-bridge circuit are the first strain unit and the second strain unit, respectively. The first strain unit is used to sense axial strain; The second strain unit includes at least two strain gauges connected in series. At least one of the strain gauges is inclined at a certain angle to the axial direction to sense circumferential strain, while the other strain gauges are suspended. The angle is used to ensure that the signal changes of adjacent first and second strain units are the same, so as to maintain the balance of the bridge circuit.

2. The measurement circuit according to claim 1, characterized in that, The first strain unit includes a number of strain gauges connected in series, the same number as in the second strain unit, and a plurality of the strain gauges in the first strain unit are arranged parallel to the axial direction.

3. The measurement circuit according to claim 1, characterized in that, The number of strain gauges included in the strain unit is set to n. When the bridge is balanced, the number of strain gauges n and the included angle θ satisfy the following formula: ； Where R0 is the resistance value of the strain gauge, K0 is the sensitivity coefficient of the strain gauge, εzp is the axial strain of the strain gauge under pressure P, εhp is the circumferential strain of the strain gauge under pressure P, and Kp is the ratio of the circumferential strain εhp to the axial strain εzp of the strain gauge when Poisson's ratio is υ.

4. A tension meter, characterized in that, include: A cylindrical body, wherein a measuring section with a thickness smaller than that at both ends is formed in the middle of the cylindrical body; A core frame is fitted into the measuring section inside the cylinder. A flexible printed circuit board is provided on the surface of the core frame, and a measuring circuit as described in any one of claims 1-3 is provided on the flexible printed circuit board. The first strain unit and the second strain unit are arranged symmetrically and alternately in the circumferential direction. The strain gauges in the first strain unit and the inclined strain gauges in the second strain unit are disposed on the surface of the core frame, and the remaining strain gauges in the second strain unit are suspended in the air above the core frame.

5. The tension meter according to claim 4, characterized in that, The core frame includes a first tube frame and a second tube frame that are nested together. The flexible printed circuit board is disposed in the first tube frame on the inner side. The two ends of the tube frame are folded outward to form end edges. The inner wall of the cylinder forms a step that abuts against the end edges.

6. The tension meter according to claim 4, characterized in that, It also includes joints that are sealed to both ends of the cylinder, and a protective sleeve that is fitted over the outside of the cylinder is provided between the two joints.

7. The tension meter according to claim 4, characterized in that, It also includes a temperature sensor disposed on the flexible printed circuit board.

8. A calculation method, characterized in that, The method for calculating the angle of the inclined strain gauge in the second strain unit as described in claim 1 includes: The static resistances of the two first strain gauges and the two second strain gauges are set to Ra, Rd, Rb and Rc respectively, where the resistance of the strain gauge is set to R0 and the sensitivity is set to K0. After applying environmental pressure P, the change in resistance of Ra is obtained. and the change in resistance of Rb ; When ΔRa = ΔRb, the bridge is balanced. Substituting... get: ; To obtain the relationship between the angle θ of the tilted strain gauge and the number of strain gauges n: .

9. The calculation method according to claim 8, characterized in that, This also includes calculating the formula based on the bridge output signal after applying the instrument tension F. Therefore, based on the output signal Uab of the full-bridge circuit, the target axial force can be calculated. .

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