Acceleration measuring instrument for underground pipe string

Abstract

The invention relates to the technical field of underground sensor equipment, in particular to an underground pipe string acceleration measuring instrument which comprises a cylindrical shell and a main control board, and the main control board is packaged and fixed in the shell and connected with a ground control instrument through a cable. A single chip microcomputer, a primary voltage conversion circuit, a secondary voltage conversion circuit, a constant-current diode, an accelerometer and a step-down circuit are loaded on the main control board; for a measuring instrument for judging whether the setting and perforation operation of a bridge plug is successful or not by using acceleration data, when the voltage of an underground cable is insufficient during ignition of an igniter wire, the detection of the acceleration generated during setting or perforation of an underground perforating gun cannot be carried out; an energy storage capacitor E1, an energy storage capacitor E2, a primary voltage conversion circuit and a secondary voltage conversion circuit are innovatively introduced, and a capacitor energy storage scheme is adopted to solve the problem of input voltage drop caused by perforation ignition.

Description

Technical Field

[0001] This invention relates to the field of downhole sensor equipment technology, and in particular to a downhole tubing string acceleration measuring instrument. Background Technology

[0002] With the development of shale gas and shale oil, a combined approach of explosive bridge plug setting and perforation is commonly used. Explosive bridge plug setting involves lowering a composite bridge plug to the designed depth via cable, then detonating the setting tool controlled by surface equipment. After the explosion, the bridge plug's slips anchor to the casing wall, and the expansion and deformation of the plug achieves an effective seal, thus isolating the fractured and unfractured sections. Perforation involves using a perforating gun to create channels in the casing and cement sheath of the target section, establishing a connection between the wellbore and the formation, providing an entry point for subsequent fracturing. Traditionally, the success of these two stages is determined primarily by monitoring indirect parameters, such as pressure and tension changes, using surface equipment. This method suffers from lag, ambiguity, and uncertainty, failing to provide direct and conclusive evidence of downhole setting and perforation failure. Failure of setting or perforation will result in the failure of fracturing in that section, causing significant economic losses.

[0003] The inventors introduced a triaxial accelerometer to monitor the acceleration generated during perforation or setting of the downhole perforating gun in real time. The measured acceleration is transmitted to the surface control unit via a single-core cable using single-core communication. The surface control unit then plots the acceleration curve in real time. Given the mass of the tubing string, the force on the tubing string can be calculated, indirectly providing data support for determining whether the bridge plug has set and whether the perforating gun has succeeded. During perforation ignition, the surface control system closes the switch, applying voltage to both ends of the bridge wire igniter. The core problem lies in the non-negligible DC resistance of the downhole cable. When the large ignition current flows through the cable resistance, a significant voltage drop occurs, causing a catastrophic drop in the input voltage at the downhole instrument, from the normal 24V to 2.5V, rendering the accelerometer inoperable. Summary of the Invention

[0004] The purpose of this invention is to provide a downhole pipe string acceleration measuring instrument to solve the problem of insufficient downhole cable voltage after ignition short circuit during bridge wire ignition.

[0005] To achieve the above objectives, the present invention provides a downhole tubing string accelerometer, comprising a cylindrical housing and a main control board. The main control board is encapsulated and fixed within the housing and connected to an uphole controller via a cable. The main control board is equipped with a microcontroller, a first-stage voltage conversion circuit, a second-stage voltage conversion circuit, a constant current diode, an accelerometer, and a step-down circuit. The output of the first-stage voltage conversion circuit is connected to the second-stage voltage conversion circuit and the step-down circuit. The second-stage voltage conversion circuit is used to output a boosted operating voltage to the accelerometer through the constant current diode. The first-stage voltage conversion circuit includes: The circuit comprises a first voltage regulator circuit, a second voltage regulator circuit, a first resistor R17, a second resistor R53, energy storage capacitors E1 and E2. The input terminals of the first and second voltage regulator circuits are connected to the positive power supply. Their output terminals are connected in parallel and then connected to the input terminal of the first resistor R17. The output terminal of the first resistor R17 is connected to the input terminal of the second resistor R53. The energy storage capacitors E1 and E2 are connected in parallel and then coupled between the output terminal of the first resistor R17 and the reference ground to power the subsequent circuits during ignition. The output terminal of the second resistor R53 is connected to the input terminal of the filter circuit to generate a stable operating voltage.

[0006] The technical solution of this invention addresses the issue of insufficient downhole cable voltage during bridge plug setting and perforation operations when the bridge wire ignites, preventing the detection of acceleration generated during downhole perforation gun setting or perforation. It innovatively introduces energy storage capacitors E1 and E2, along with the primary and secondary voltage conversion circuits, employing a boost circuit and capacitor energy storage to solve the problem of input voltage drop caused by perforation ignition.

[0007] The filter circuit includes a Zener diode Z2 and a multi-stage filter capacitor network connected in parallel with it. The cathode of the Zener diode Z2 is grounded, and its anode is connected to the output terminal of the second resistor R53. The multi-stage filter capacitor network is composed of multiple capacitors of different capacitance values ​​connected in parallel. One end of the capacitors is connected to the anode of the Zener diode Z2, and the other end is grounded to output a stable operating voltage.

[0008] The Zener diode Z2 mainly serves as a voltage regulator and protection unit, and the multi-stage filter capacitor network performs filtering based on the capacitance of its parallel capacitors.

[0009] The multi-stage filter capacitor network includes a first filter capacitor C50, a second filter capacitor C11, a third filter capacitor C10, and a fourth filter capacitor C12 connected in parallel. The capacitance values ​​of the first filter capacitor C50, the second filter capacitor C11, the third filter capacitor C10, and the fourth filter capacitor C12 differ by at least one order of magnitude to collaboratively filter out noise of different frequencies.

[0010] The capacitance values ​​of the first filter capacitor C50, the second filter capacitor C11, the third filter capacitor C10, and the fourth filter capacitor C12 differ by at least one order of magnitude. This design allows each capacitor to present a low-impedance path to noise at a specific frequency, thereby helping to eliminate noise and significantly improving the purity and stability of the operating voltage of the subsequent accelerometer.

[0011] The first voltage regulator circuit includes a first diode D1, a first MOSFET Q4, a third resistor R65, a TVS5, a first capacitor C8, a second capacitor C17, a second diode D3, and a first varistor Z4. The input terminal of the first diode D1 is connected to the positive power supply terminal, and the output terminal of the first diode D1 is connected to the drain of the first MOSFET Q4. The source of the first MOSFET Q4 is connected to one end of the third resistor R65, one end of the second diode D3, one end of the TVS5, and one end of the second capacitor C17, and is also connected to the anode of the second diode D3. The gate of the first MOSFET Q4 is connected to one end of the first capacitor C8, one end of the first varistor Z4, the other end of the third resistor R65, and the other end of the TVS5. The other end of the first capacitor C8 is connected to the other end of the second capacitor C17, the other end of the first varistor Z4, and a reference ground. The cathode of the second diode D3 is connected to the second voltage regulator circuit and then to the first resistor R17.

[0012] The second voltage regulator circuit includes a third diode D5, a second MOSFET Q5, a fourth resistor R33, a TVS7, a third capacitor C25, a fourth capacitor C27, a fourth diode D7, and a second varistor Z5. The input terminal of the first diode D1 is connected to the positive power supply terminal. The output terminal of the second diode D5 is connected to the drain of the second MOSFET Q5. The source of the second MOSFET Q5 is connected to one end of the fourth resistor R33, one end of the third diode D5, one end of the TVS7, and one end of the fourth capacitor C27, and is also connected to the anode of the fourth diode D7. The gate of the second MOSFET Q5 is connected to one end of the third capacitor C25, one end of the second varistor Z5, the other end of the fourth resistor R33, and the other end of the TVS7. The other end of the third capacitor C25 is connected to the other end of the fourth capacitor C27, the other end of the second varistor Z5, and a reference ground. The cathode of the third diode D5 is connected to the first voltage regulator circuit and then to the first resistor R17.

[0013] The first voltage regulator circuit and the second voltage regulator circuit are connected in parallel to distribute the current roughly, avoiding the single MOSFET from overheating due to bearing all the power consumption. At the same time, after the two circuits are connected in parallel, the output voltage fluctuation will be smaller when the load current changes suddenly, which helps to output a clean voltage.

[0014] The secondary voltage conversion circuit includes a control chip U3, a switch control circuit, and an LC filter circuit. The input terminal of the switch control circuit is connected to the output of the primary voltage conversion circuit. The control chip U3 is coupled between the switch control circuit and the LC filter circuit. The output terminal of the LC filter circuit is connected to the input terminal of the constant current diode.

[0015] In the secondary voltage conversion circuit, in order to manage the accelerometer, the switch control circuit is used as the switch of the secondary voltage conversion circuit, the control chip U3 controls each component, and the LC filter circuit is used to filter out noise.

[0016] The switching control circuit includes a first voltage divider resistor R73, a second voltage divider resistor R146, a third MOSFET Q11, a fourth MOSFET Q8, a pull-down resistor R173, and a current-limiting resistor R174. The source of the third MOSFET Q11 is connected to the positive power supply terminal, and its drain serves as the voltage output of the switching control circuit. The first voltage divider resistor R73 is connected between the positive power supply terminal and the gate of the third MOSFET Q11. The drain of the fourth MOSFET Q8 is connected to the gate of the third MOSFET Q11 through the second voltage divider resistor R146, and its source is grounded. The pull-down resistor R173 is connected between the gate of the fourth MOSFET Q8 and the reference ground.

[0017] The first voltage divider resistor R73, together with the second voltage divider resistor R146, forms a voltage divider network, and the state of the control signal is ensured by a pull-down resistor to improve reliability during short circuits.

[0018] The LC filter circuit includes a first LC filter network and a second LC filter network. The first LC filter network is connected between the output terminal of the switch control circuit and the input terminal of the control chip U3, and the second LC filter network is connected between the control chip U3 and the subsequent circuit. The first LC filter network is composed of a first inductor L5 and a fifth capacitor C48, and the second filter network is composed of a second inductor L3, a sixth capacitor C9, and a seventh capacitor C4.

[0019] The first LC filter network performs initial filtering on the output voltage of the front-end switch control circuit and prevents noise backflow. The second LC filter network is used to filter out the noise generated by the control chip U3.

[0020] This invention relates to a downhole pipe string accelerometer. Addressing the problem of insufficient cable voltage during ignition short circuits when the bridge wire ignites, the circuit design utilizes a primary conversion circuit in conjunction with a secondary conversion circuit to solve the problem of insufficient downhole cable voltage during bridge wire ignition by adding a capacitor for energy storage. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of a downhole tubing acceleration measuring instrument according to the present invention.

[0023] Figure 2 This is a block diagram of the main control board of a downhole pipe string acceleration measuring instrument according to the present invention.

[0024] Figure 3 This is a primary voltage conversion circuit diagram of a downhole pipe string acceleration measuring instrument according to the present invention.

[0025] Figure 4 This is a circuit diagram of a downhole pipe string acceleration measuring instrument according to the present invention.

[0026] In the attached diagram, 1 represents the housing; 2 represents the main control board. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] Please see Figures 1 to 4 This invention provides a downhole tubing string accelerometer, comprising a cylindrical housing and a main control board. The main control board is encapsulated and fixed within the housing and connected to an uphole controller via a cable. The main control board carries a microcontroller, a first-stage voltage conversion circuit, a second-stage voltage conversion circuit, a constant current diode, an accelerometer, and a step-down circuit. The output of the first-stage voltage conversion circuit is connected to the second-stage voltage conversion circuit and the step-down circuit. The second-stage voltage conversion circuit is used to output a boosted operating voltage to the accelerometer through the constant current diode. The first-stage voltage conversion circuit includes: The circuit comprises a first voltage regulator circuit, a second voltage regulator circuit, a first resistor R17, a second resistor R53, energy storage capacitors E1 and E2. The input terminals of the first and second voltage regulator circuits are connected to the positive power supply. Their output terminals are connected in parallel and then connected to the input terminal of the first resistor R17. The output terminal of the first resistor R17 is connected to the input terminal of the second resistor R53. The energy storage capacitors E1 and E2 are connected in parallel and then coupled between the output terminal of the first resistor R17 and the reference ground to power the subsequent circuits during ignition. The output terminal of the second resistor R53 is connected to the input terminal of the filter circuit to generate a stable operating voltage.

[0029] Please see Figure 1 The accelerometer described in this application is coupled to this system. When the ignition module is connected to the bridge wire igniter, the downhole cable voltage will be pulled down to 2.5V, while the power supply voltage of the 3-axis accelerometer inside the accelerometer needs to be maintained at 24V for the accelerometer sensor to function properly. Please refer to [link to relevant documentation]. Figure 2 The accelerometer uses a microcontroller (specifically PIC24HJ128GP506A) as its control core. Signals from the three-axis acceleration (X, Y, and Z axes) are fed into an ADC chip (AD7091) via a follower. The AD7091 interacts with the microcontroller via SPI. Eight EEPROMs interact with the microcontroller via SPI. JTAG is used for microcontroller programming. The microcontroller communicates with the cable via a detection and response circuit. The cable voltage is converted to 20V via a first-stage voltage conversion circuit, and then boosted to 24V via a second-stage voltage conversion circuit. The 3-axis accelerometer is powered by three constant current diodes, and a 7V output is provided through a step-down circuit. Of course, there can be multiple step-down circuits in this application. The voltage is reduced step-by-step through the step-down circuit to power the microcontroller and the eight EEPROMs respectively. Since there are many existing technologies, each step-down circuit is not specifically described in this application. The 7V voltage is then output as 3.3V through the step-down circuit to power the microcontroller and the eight EEPROMs. The power-off of the secondary voltage conversion circuit and the step-down circuit is controlled by the microcontroller.

[0030] Furthermore, the filter circuit includes a Zener diode Z2 and a multi-stage filter capacitor network connected in parallel with it. The cathode of the Zener diode Z2 is grounded, and its anode is connected to the output terminal of the second resistor R53. The multi-stage filter capacitor network is composed of multiple capacitors of different capacitance values ​​connected in parallel. One end of the capacitors is connected to the anode of the Zener diode Z2, and the other end is grounded to output a stable operating voltage.

[0031] The multi-stage filter capacitor network includes a first filter capacitor C50, a second filter capacitor C11, a third filter capacitor C10, and a fourth filter capacitor C12 connected in parallel. The capacitance values ​​of the first filter capacitor C50, the second filter capacitor C11, the third filter capacitor C10, and the fourth filter capacitor C12 differ by at least one order of magnitude to collaboratively filter out noise of different frequencies. The Zener diode Z2 is used for voltage regulation and protection.

[0032] Furthermore, the first voltage regulator circuit includes a first diode D1, a first MOSFET Q4, a third resistor R65, a TVS5, a first capacitor C8, a second capacitor C17, a second diode D3, and a first varistor Z4. The input terminal of the first diode D1 is connected to the positive power supply terminal, and the output terminal of the first diode D1 is connected to the drain of the first MOSFET Q4. The source of the first MOSFET Q4 is connected to one end of the third resistor R65, one end of the second diode D3, one end of the TVS5, and one end of the second capacitor C17, and is also connected to the anode of the second diode D3. The gate of the first MOSFET Q4 is connected to one end of the first capacitor C8, one end of the first varistor Z4, the other end of the third resistor R65, and the other end of the TVS5. The other end of the first capacitor C8 is connected to the other end of the second capacitor C17, the other end of the first varistor Z4, and a reference ground. The cathode of the second diode D3 is connected to the second voltage regulator circuit and then to the first resistor R17.

[0033] The second voltage regulator circuit includes a third diode D5, a second MOSFET Q5, a fourth resistor R33, a TVS7, a third capacitor C25, a fourth capacitor C27, a fourth diode D7, and a second varistor Z5. The input terminal of the first diode D1 is connected to the positive power supply terminal. The output terminal of the second diode D5 is connected to the drain of the second MOSFET Q5. The source of the second MOSFET Q5 is connected to one end of the fourth resistor R33, one end of the third diode D5, one end of the TVS7, and one end of the fourth capacitor C27, and is also connected to the anode of the fourth diode D7. The gate of the second MOSFET Q5 is connected to one end of the third capacitor C25, one end of the second varistor Z5, the other end of the fourth resistor R33, and the other end of the TVS7. The other end of the third capacitor C25 is connected to the other end of the fourth capacitor C27, the other end of the second varistor Z5, and a reference ground. The cathode of the third diode D5 is connected to the first voltage regulator circuit and then to the first resistor R17.

[0034] In this embodiment, the first-stage voltage conversion circuit converts the voltage from 30-450V to 22V using dual depletion-type MOSFETs IXTA3N50D2 to power the subsequent circuit, which is expected to draw 25mA. When ignition is performed using a bridge wire, the two fully charged 470uF capacitors E1 and E2 discharge to power the subsequent circuit. The discharge time is calculated as 0.025A * 500ms / (22V - 5V) = 735uF. After ignition short circuit, capacitors E1 and E2, totaling 940uF, provide 500ms of operating energy to the system. If it is necessary to extend the acceleration acquisition time, the capacitors can be replaced with 1000uF capacitors. The first diode D1, the third diode D5, the fourth diode D7, and the second diode D3 serve as anti-reverse diodes to prevent the subsequent circuit from igniting. In case of failure and high voltage backflow, the first varistor Z4 and the second varistor Z5 provide a stable 20V voltage to the gate. The TVS5 and TVS7 protect the gate and source of the first MOSFET Q4 and the second MOSFET Q5. The third resistor R65 and the fourth resistor R33 provide a voltage difference between the gate and the source. The first capacitor C8 and the third capacitor C25 are used to buffer and protect the Zener diode. The first MOSFET Q4 and the second MOSFET Q5 are used to automatically turn on and adjust the voltage. The first resistor R17 is used to limit the current.

[0035] Furthermore, the secondary voltage conversion circuit includes a control chip U3, a switch control circuit, and an LC filter circuit. The input terminal of the switch control circuit is connected to the output of the primary voltage conversion circuit. The control chip U3 is coupled between the switch control circuit and the LC filter circuit. The output terminal of the LC filter circuit is connected to the input terminal of the constant current diode.

[0036] The switch control circuit includes a first voltage divider resistor R73, a second voltage divider resistor R146, a third MOSFET Q11, a fourth MOSFET Q8, a pull-down resistor R173, and a current-limiting resistor R174. The source of the third MOSFET Q11 is connected to the positive power supply terminal, and its drain serves as the voltage output of the switch control circuit. The first voltage divider resistor R73 is connected between the positive power supply terminal and the gate of the third MOSFET Q11. The drain of the fourth MOSFET Q8 is connected to the gate of the third MOSFET Q11 through the second voltage divider resistor R146, and its source is grounded. The pull-down resistor R173 is connected between the gate of the fourth MOSFET Q8 and the reference ground.

[0037] The LC filter circuit includes a first LC filter network and a second LC filter network. The first LC filter network is connected between the output terminal of the switch control circuit and the input terminal of the control chip U3, and the second LC filter network is connected between the control chip U3 and the subsequent circuit. The first LC filter network is composed of a first inductor L5 and a fifth capacitor C48, and the second filter network is composed of a second inductor L3, a sixth capacitor C9, and a seventh capacitor C4.

[0038] The first voltage divider resistor R73 and the second voltage divider resistor R146 act as voltage dividers, preventing the gate-source voltage of the third MOSFET Q11 from becoming too high and burning out. They also limit current, protecting the fourth MOSFET Q8 from burning out due to overcurrent. When power is needed for the sensor, the microcontroller enables the XYZ_ON and Power_ON pins. After the Power_ON pin is pulled high, the fourth MOSFET Q8 conducts. The voltage difference between the first and second voltage divider resistors R73 and R146 provides a voltage difference to the gate-source of the third MOSFET Q11, turning it on. The +22V power supply then powers chip U3. With XYZ_ON enabled, U3 provides a stable 24V voltage to the accelerometer. When power is not needed for the sensor, the microcontroller pulls the XYZ_ON and Power_ON pins low, turning off the third MOSFET Q11 and control chip U3. L3, E4, and E5 form a π-type LC filter circuit, making the 24V voltage from the sensor more stable and cleaner. When the secondary voltage conversion circuit collects acceleration after ignition, it turns on the third MOS transistor Q11, and the boost circuit works to boost the voltage stored in the capacitor to 24V to power the 3-axis accelerometer.

[0039] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A downhole tubular acceleration measuring instrument, characterized in that, The device includes a cylindrical housing and a main control board. The main control board is encapsulated and fixed inside the housing and connected to the wellhead controller via a cable. The main control board is equipped with a microcontroller, a first-stage voltage conversion circuit, a second-stage voltage conversion circuit, a constant current diode, an accelerometer, and a step-down circuit. The output of the first-stage voltage conversion circuit is connected to the second-stage voltage conversion circuit and the step-down circuit. The second-stage voltage conversion circuit is used to output a boosted operating voltage to the accelerometer through the constant current diode. The first-stage voltage conversion circuit includes: The circuit comprises a first voltage regulator circuit, a second voltage regulator circuit, a first resistor R17, a second resistor R53, energy storage capacitors E1 and E2. The input terminals of the first and second voltage regulator circuits are connected to the positive power supply. Their output terminals are connected in parallel and then connected to the input terminal of the first resistor R17. The output terminal of the first resistor R17 is connected to the input terminal of the second resistor R53. The energy storage capacitors E1 and E2 are connected in parallel and then coupled between the output terminal of the first resistor R17 and the reference ground to power the subsequent circuits during ignition. The output terminal of the second resistor R53 is connected to the input terminal of the filter circuit to generate a stable operating voltage.

2. The downhole tubing string acceleration measuring instrument as described in claim 1, characterized in that, The filtering circuit includes a Zener diode Z2 and a multi-stage filtering capacitor network connected in parallel with it. The cathode of the Zener diode Z2 is grounded, and its anode is connected to the output terminal of the second resistor R53. The multi-stage filtering capacitor network is composed of multiple capacitors of different capacitance values ​​connected in parallel. One end of the capacitors is connected to the anode of the Zener diode Z2, and the other end is grounded to output a stable operating voltage.

3. The downhole tubing string acceleration measuring instrument as described in claim 2, characterized in that, The multi-stage filter capacitor network includes a first filter capacitor C50, a second filter capacitor C11, a third filter capacitor C10, and a fourth filter capacitor C12 connected in parallel. The capacitance values ​​of the first filter capacitor C50, the second filter capacitor C11, the third filter capacitor C10, and the fourth filter capacitor C12 differ by at least one order of magnitude to collaboratively filter out noise of different frequencies.

4. A downhole tubing string acceleration measuring instrument as described in any one of claims 1 to 3, characterized in that, The first voltage regulator circuit includes a first diode D1, a first MOSFET Q4, a third resistor R65, a TVS5, a first capacitor C8, a second capacitor C17, a second diode D3, and a first varistor Z4. The input terminal of the first diode D1 is connected to the positive power supply terminal, and the output terminal of the first diode D1 is connected to the drain of the first MOSFET Q4. The source of the first MOSFET Q4 is connected to one end of the third resistor R65, one end of the second diode D3, one end of the TVS5, and one end of the second capacitor C17, and is also connected to the anode of the second diode D3. The gate of the first MOSFET Q4 is connected to one end of the first capacitor C8, one end of the first varistor Z4, the other end of the third resistor R65, and the other end of the TVS5. The other end of the first capacitor C8 is connected to the other end of the second capacitor C17, the other end of the first varistor Z4, and a reference ground. The cathode of the second diode D3 is connected to the second voltage regulator circuit and then to the first resistor R17.

5. A downhole tubing string acceleration measuring instrument as described in any one of claims 1 to 3, characterized in that, The second voltage regulator circuit includes a third diode D5, a second MOSFET Q5, a fourth resistor R33, a TVS7, a third capacitor C25, a fourth capacitor C27, a fourth diode D7, and a second varistor Z5. The input terminal of the first diode D1 is connected to the positive power supply terminal. The output terminal of the second diode D5 is connected to the drain of the second MOSFET Q5. The source of the second MOSFET Q5 is connected to one end of the fourth resistor R33, one end of the third diode D5, one end of the TVS7, and one end of the fourth capacitor C27, and is also connected to the anode of the fourth diode D7. The gate of the second MOSFET Q5 is connected to one end of the third capacitor C25, one end of the second varistor Z5, the other end of the fourth resistor R33, and the other end of the TVS7. The other end of the third capacitor C25 is connected to the other end of the fourth capacitor C27, the other end of the second varistor Z5, and a reference ground. The cathode of the third diode D5 is connected to the first voltage regulator circuit and then to the first resistor R17.

6. The downhole tubing string acceleration measuring instrument as described in claim 1, characterized in that, The secondary voltage conversion circuit includes a control chip U3, a switch control circuit, and an LC filter circuit. The input terminal of the switch control circuit is connected to the output of the primary voltage conversion circuit. The control chip U3 is coupled between the switch control circuit and the LC filter circuit. The output terminal of the LC filter circuit is connected to the input terminal of the constant current diode.

7. The downhole tubing string acceleration measuring instrument as described in claim 6, characterized in that, The switch control circuit includes a first voltage divider resistor R73, a second voltage divider resistor R146, a third MOSFET Q11, a fourth MOSFET Q8, a pull-down resistor R173, and a current-limiting resistor R174. The source of the third MOSFET Q11 is connected to the positive power supply terminal, and its drain serves as the voltage output of the switch control circuit. The first voltage divider resistor R73 is connected between the positive power supply terminal and the gate of the third MOSFET Q11. The drain of the fourth MOSFET Q8 is connected to the gate of the third MOSFET Q11 through the second voltage divider resistor R146, and its source is grounded. The pull-down resistor R173 is connected between the gate of the fourth MOSFET Q8 and the reference ground.

8. A downhole tubing string acceleration measuring instrument as described in claim 6, characterized in that, The LC filter circuit includes a first LC filter network and a second LC filter network. The first LC filter network is connected between the output terminal of the switch control circuit and the input terminal of the control chip U3, and the second LC filter network is connected between the control chip U3 and the subsequent circuit. The first LC filter network is composed of a first inductor L5 and a fifth capacitor C48, and the second filter network is composed of a second inductor L3, a sixth capacitor C9, and a seventh capacitor C4.

Images