Tension sensor measuring circuit and tensiometer

Abstract

The invention belongs to the technical field of underground tension measurement, and particularly relates to a tension sensor measuring circuit and a tensiometer. The device comprises four groups of strain units which are sequentially connected to form a full-bridge circuit, and the strain units on oppositely arranged bridge arms of the full-bridge circuit are respectively a first strain unit and a second strain unit; the two first strain units are arranged in parallel to the axial direction and are used for sensing axial strain; a certain included angle is formed between the two second strain units and the axial direction and is used for sensing circumferential strain; the strain sensitivity coefficient of the second strain unit is different from that of the first strain unit, so that the signal variation of the adjacent first strain unit and second strain unit is the same. The method is used for solving the problems that tension measurement is complex and high in cost, 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 structural 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 and a tension meter. 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, a tension sensor measurement circuit and tension meter are provided to solve the problems of complex and costly tension measurement.

[0009] 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 oppositely arranged bridge arms of the full bridge circuit are respectively a first strain unit and a second strain unit;

[0010] The two first strain units are arranged parallel to the axial direction for sensing axial strain.

[0011] The two second strain units form a certain angle with the axial direction to be used to sense circumferential strain;

[0012] The strain sensitivity coefficient of the second strain unit is different from that of the first strain unit, so as to make the signal change of adjacent first and second strain units the same, so as to maintain bridge balance and eliminate signal interference.

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

[0014] In one embodiment, each strain unit includes at least one strain gauge, wherein the strain gauge in the second strain unit is arranged perpendicular to the axial direction for sensing circumferential strain.

[0015] In one embodiment, the ratio of the strain sensitivity coefficients of the first strain unit to the second strain unit is Kp, which is used to make the signal change amounts of adjacent first strain units and second strain units the same.

[0016] This embodiment also discloses a tension meter, which includes:

[0017] 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;

[0018] 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 symmetrically arranged alternately along the circumferential direction on the surface of the core frame.

[0019] 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.

[0020] 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.

[0021] In one embodiment, a temperature sensor is also included on the flexible printed circuit board.

[0022] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0023] 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.

[0024] 2. 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 (εhp = Kp * εzp). 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.

[0025] 3. 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.

[0026] 4. 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

[0027] 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.

[0028] Figure 1 This is a schematic diagram of the tension sensor measurement circuit of the present invention.

[0029] Figure 2 This is a schematic diagram of the tension meter of the present invention;

[0030] Figure 3 This is a schematic diagram of the core frame in the tension meter of the present invention.

[0031] Figure label:

[0032] 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

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Example 1

[0039] like Figure 1 As shown, the tension sensor measurement circuit provided by the present invention includes four sets of strain units, which are connected in sequence to form a full-bridge circuit. The strain units on the oppositely arranged bridge arms of the full-bridge circuit are respectively the first strain unit and the second strain unit.

[0040] The two first strain units are arranged parallel to the axial direction for sensing axial strain.

[0041] The two second strain units form a certain angle with the axial direction to be used to sense circumferential strain;

[0042] The strain sensitivity coefficient of the second strain unit is different from that of the first strain unit, so that the impedance changes generated by the circumferential strain εhp and the axial strain εzp are the same and are eliminated by the bridge balance, so that the signal changes of adjacent first strain units and second strain units are the same, thereby maintaining bridge balance and eliminating signal interference.

[0043] In this embodiment, since it is used in well logging, the axial direction is the vertical Z-axis.

[0044] Specifically, each strain unit includes at least one strain gauge. In this embodiment, each strain unit is provided with one strain gauge. In the second strain unit, the strain gauge is arranged perpendicular to the axial direction and is used to sense circumferential strain.

[0045] Specifically, the technical principle for achieving pressure balance is as follows:

[0046] As shown in the figure, strain gauges with different sensitivities are used. Strain gauges Rb and Rc are mounted parallel to the Z-axis, and the sensitive strain gauge εz is mounted perpendicular to the Z-axis, while Ra and Rd are mounted perpendicular to the Z-axis. The static resistances of the four strain gauges are Ra, Rb, Rc, and Rd, respectively, and their strain sensitivity coefficients are Ka, Kb, Kc, and Kd, respectively. The design aims to satisfy the following conditions regarding the initial resistance and sensitivity coefficients:

[0047] ;

[0048] ;

[0049] ;

[0050] In this way, the ratio of the strain sensitivity coefficients of the first strain unit and the second strain unit is Kp, which is used to make the signal change of adjacent first strain units and second strain units the same; the purpose is to reduce the sensitivity of Ka and Kd.

[0051] The voltage across the bridge power supply is U, and the output signal is... .

[0052] When the initial pressure P=0 and the tension Fz=0, Bridge balance, output signal .

[0053] When in use, the εhp and εzp generated under pressure P (since εhp and εzp are both negative under external pressure P) are calculated as follows:

[0054] Resistance change of Ra strain gauge ;

[0055] because: Therefore, we get: ;

[0056] Furthermore, we can obtain: ;

[0057] Resistance change of Rb strain gauge ;

[0058] then: Similarly, ;

[0059] Therefore, the output voltage .

[0060] By setting the ratio of the sensitivity coefficients of the first strain unit and the second strain unit to Kp, the signal changes of adjacent first strain units and second strain units can be made to be the same.

[0061] Furthermore, the axial strain, axial stress, and axial force can be obtained.

[0062] The calculation process is as follows:

[0063] Under the action of instrument tension Fz (N), Rb and Rc are normally sensitive to axial strain εzf; while Ra and Rd sense the circumferential strain caused by Poisson's ratio, and their sensitivity is also reduced.

[0064] Resistance change of Ra strain gauge (The strain is negative under external pressure).

[0065] Resistance change of Rb strain gauge ;

[0066] Resistance change of Rc strain gauge ;

[0067] Resistance change of Rd strain gauge ;

[0068] According to the formula for calculating the output signal of the bridge ;

[0069] In this case, εzf and Fz are in the same direction and have the same sign, with the tension being positive and the thrust being negative.

[0070] Therefore, the formulas for calculating axial strain εz, axial stress σzf, and axial force Fz based on the measured output signal Uab can be obtained:

[0071] ;

[0072] ;

[0073] ;

[0074] Where Fz and Uab are in the same direction and have the same sign, positive voltage represents tension, and negative voltage represents thrust; A is the cross-sectional area of ​​the thick-walled tube being measured, specifically... υ is the Poisson's ratio of the material. For example, when υ is 0.3, Kp is 4.25, and when υ is 0.305, Kp is 4.3462.

[0075] This embodiment uses a suitable arrangement of 4 (or 4 groups) strain gauges, each (or group) serving as a bridge arm resistor of a Wheatstone bridge. Each pair of adjacent bridge arms (e.g., group A, group B, whose equivalent resistances are denoted as Ra and Rb respectively) is shown in the figure. Ra primarily senses the axial strain εz, and Rb primarily senses the circumferential strain εh, ensuring that under pressure P, Ra and Rb exhibit the same resistance change. If the pressure P affects the potential of the common terminal Ua of Ra and Rb, then the effect of the pressure P on the potential will be eliminated.

[0076] Example 2

[0077] like Figure 2 and 3 As shown, this embodiment also discloses a tension meter, which includes: a cylinder 2, a core frame, and the measuring circuit in embodiment 1.

[0078] A measuring section with a thickness less than that at both ends is formed in the middle of the cylinder; the core frame is matched and snapped into the measuring section inside the cylinder, and a flexible printed plate is provided on the surface of the core frame. The flexible printed plate is provided with the measuring circuit as described in Embodiment 1 above, and the first strain unit and the second strain unit are symmetrically arranged alternately along the circumferential direction on the surface of the core frame.

[0079] The flexible printed circuit board 2e is wound and attached to the outer surface of a tubular core frame. The core frame, along with the flexible circuit board on it, is then inserted into the inner cavity of the tension meter measuring section. The solder joint 2f on the flexible circuit board leads out the bridge signal through the lead wire 2g.

[0080] 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.

[0081] 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.

[0082] like Figure 2As 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.

[0083] 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.

[0084] 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; and these 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 two first strain units are arranged parallel to the axial direction for sensing axial strain. The two second strain units form a certain angle with the axial direction to be used to sense circumferential strain; The strain sensitivity coefficient of the second strain unit is different from that of the first strain unit, so as to make the signal change amount of adjacent first strain units and second strain units the same, so as to maintain the bridge balance.

2. The tension sensor measuring circuit according to claim 1, characterized in that, Each strain unit includes at least one strain gauge, and the strain gauge in the second strain unit is arranged perpendicular to the axial direction to sense circumferential strain.

3. The tension sensor measuring circuit according to claim 2, characterized in that, The ratio of the strain sensitivity coefficients of the first strain unit to the second strain unit is Kp, which is used to make the signal change amount of adjacent first strain units and second strain units the same.

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 symmetrically and alternately arranged on the surface of the core frame in a circumferential direction.

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.

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