Micro-miniature bridge circuit adjustable dynamic strain measurement device

Abstract

The utility model provides a microminiature bridge circuit adjustable dynamic strain measuring device which comprises a double-layer circuit board. The double-layer circuit board comprises a first circuit board used for installing an MCU control module, a display and an SD card, and a second circuit board used for installing a bridge circuit, a signal conditioning circuit and a power supply circuit. The first circuit board and the second circuit board are rectangular, are arranged in parallel and are fixedly connected. According to the utility model, installation positions are provided for the MCU control module, the display, the SD card, the bridge circuit, the signal conditioning circuit and the power supply circuit through the first circuit board and the second circuit board of the double-layer circuit board, and the first circuit board and the second circuit board are arranged in parallel and are fixedly connected, so that the space utilization rate of the system is improved; the device occupies a smaller space, and solves the problem that the inspection personnel are inconvenient to carry and install a measuring device with a larger volume.

Description

Technical Field

[0001] The utility model relates to the technical field of structural vibration dynamic strain measurement, in particular to a micro-bridge adjustable dynamic strain measurement device. Background Art

[0002] Structural vibration is a common problem in life. We usually evaluate the vibration intensity by measuring the local strain of the structure, and then further provide strategies to deal with structural vibration. The Wheatstone bridge used for strain measurement is divided into single-arm, half-bridge and full-bridge, but most strain measurement systems currently usually switch bridges by changing the wiring, which is very inconvenient in practical application. In addition, since some structures are located in the wild and high-altitude environment, it is inconvenient for inspection personnel to carry and install large-volume measuring devices, and it is inconvenient to frequently replace or charge the batteries of the measuring devices. Utility Model Content

[0003] In order to solve the problem that it is inconvenient for inspection personnel to carry and install a large-volume measuring device, the utility model provides a micro-bridge adjustable dynamic strain measuring device, including a double-layer circuit board;

[0004] The double-layer circuit board includes a first circuit board for mounting an MCU control module, a display and an SD card, and a second circuit board for mounting a bridge circuit, a signal conditioning circuit and a power supply circuit;

[0005] The first circuit board and the second circuit board are both rectangular, arranged in parallel, and fixedly connected.

[0006] Preferably, the first circuit board and the second circuit board are both arranged in a horizontal direction;

[0007] The MCU control module, the SD card, the bridge circuit, the signal conditioning circuit and the power supply circuit are located between the first circuit board and the second circuit board;

[0008] The display is mounted on the upper side of the first circuit board.

[0009] Preferably, the device further comprises a rectangular protective housing extending in the horizontal direction;

[0010] The first circuit board is mounted on the top wall of the protection housing.

[0011] Preferably, the protective shell includes an upper shell located on the upper side and a lower shell located on the lower side;

[0012] The upper shell and the lower shell are both provided with openings;

[0013] The opening of the upper shell is located at the lower side of the upper shell;

[0014] The opening of the lower shell is located on the upper side of the lower shell;

[0015] The opening of the upper shell is snap-fitted with the opening of the lower shell to form a complete protective shell.

[0016] Preferably, bolt connection columns are provided at the four inner corners of the upper shell and the lower shell;

[0017] The protective shell also includes bolts arranged from bottom to top;

[0018] The head of the bolt is located in the bolt connection column of the lower shell, and the tail of the bolt is threadedly connected in the bolt connection column of the upper shell.

[0019] Preferably, the top opening of the upper housing has a receiving opening for receiving the display;

[0020] The display is accommodated in the accommodation opening.

[0021] Preferably, the bridge circuit includes strain gauge terminals;

[0022] A terminal receiving hole is provided on a side wall of one end of the upper housing;

[0023] The strain gauge terminal is embedded in the terminal accommodating hole.

[0024] Preferably, an operation and observation port is provided on a side wall of one end portion of the upper shell.

[0025] Preferably, the operation and observation port is covered with a cover plate.

[0026] Preferably, a battery is installed on the lower side of the second circuit board.

[0027] Compared with the prior art, the beneficial effects of the utility model are:

[0028] The utility model provides a miniature bridge-type adjustable dynamic strain measuring device, comprising a double-layer circuit board; the double-layer circuit board comprises a first circuit board for installing an MCU control module, a display and an SD card, and a second circuit board for installing a bridge circuit, a signal conditioning circuit and a power supply circuit; the first circuit board and the second circuit board are both rectangular, arranged in parallel, and fixedly connected. The utility model provides installation positions for the MCU control module, the display, the SD card, the bridge circuit, the signal conditioning circuit and the power supply circuit through the first circuit board and the second circuit board of the double-layer circuit board, and the first circuit board and the second circuit board are arranged in parallel and fixedly connected, thereby improving the space utilization of the system, making it occupy a smaller space, and solving the problem that it is inconvenient for inspection personnel to carry and install large-volume measuring devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a micro-bridge adjustable dynamic strain measuring device of the utility model;

[0030] Figure 2 It is a structural schematic diagram of a micro-bridge adjustable dynamic strain measuring device with a zero adjustment button and a bridge switch set on one side of the utility model;

[0031] Figure 3 It is a schematic diagram of the structure of the protective shell on one side of the operation and observation port of the utility model;

[0032] Figure 4 It is a schematic diagram of the structure of the protective housing on one side of the strain gauge terminal of the utility model;

[0033] Figure 5 This is a schematic diagram of the internal structure of the protective housing for removing the cover plate of the utility model;

[0034] Figure 6 This is a schematic diagram of a bridge circuit module of the utility model;

[0035] Figure 7 This is a structural block diagram of the signal conditioning circuit of the utility model;

[0036] Figure 8 This is a schematic diagram of the power supply circuit structure of the utility model;

[0037] Fig. 9 This is a hardware design diagram of the micro-bridge adjustable dynamic strain measurement system of the utility model.

[0038] Among them, 1. first circuit board; 2. second circuit board; 3. protective shell; 4. upper shell; 5. lower shell; 6. display; 7. strain gauge terminal; 8. zero adjustment button; 9. bridge setting switch; 10. charging port; 11. power indicator light; 12. cover; 13. battery. DETAILED DESCRIPTION

[0039] In order to better understand the present invention, the present invention is further described below with reference to the accompanying drawings and examples.

[0040] The utility model provides a miniature bridge-adjustable dynamic strain measuring device, which provides installation positions for an MCU control module, a display, an SD card, a bridge circuit, a signal conditioning circuit and a power supply circuit through a first circuit board and a second circuit board of a double-layer circuit board, and the first circuit board and the second circuit board are both arranged in parallel and fixedly connected, thereby improving the space utilization rate of the system, making it occupy a smaller space, and solving the problem that it is inconvenient for inspection personnel to carry and install a large-volume measuring device.

[0041] Embodiment 1:

[0042] A miniature bridge-type adjustable dynamic strain measuring device, such as Figure 1 and Figure 2 As shown, it includes a double-layer circuit board; the double-layer circuit board includes a first circuit board 1 for installing an MCU control module, a display 6 and an SD card, and a second circuit board 2 for installing a bridge circuit, a signal conditioning circuit and a power supply circuit; the first circuit board 1 and the second circuit board 2 are both rectangular, arranged in parallel, and fixedly connected.

[0043] The first circuit board 1 and the second circuit board 2 are arranged in the horizontal direction; the MCU control module, the SD card, the bridge circuit, the signal conditioning circuit and the power supply circuit are located between the first circuit board 1 and the second circuit board 2; the display 6 is installed on the upper side of the first circuit board 1. The battery 13 is installed on the lower side of the second circuit board 2. In this embodiment, the first circuit board 1 and the second circuit board 2 are connected by bolts. In order to increase the service life of the bolts, a protective cover is provided on the outer side of the threaded rod of the bolt. In order to increase the connection strength of the bolt, the lower end of the threaded rod of the bolt passes through the second circuit board 2 and is threadedly connected with the bolt, and the bolt is pressed against the second circuit board 2.

[0044] The micro bridge adjustable dynamic strain measuring device also includes a rectangular protective housing 3 extending in the horizontal direction. Figure 3 and Figure 4As shown in the figure, the first circuit board 1 is installed on the top wall of the protective shell 3. The protective shell 3 includes an upper shell 4 located on the upper side and a lower shell 5 located on the lower side; both the upper shell 4 and the lower shell 5 are provided with openings; the opening of the upper shell 4 is located on the lower side of the upper shell 4; the opening of the lower shell 5 is located on the upper side of the lower shell 5; the opening of the upper shell 4 is snapped with the opening of the lower shell 5 to form a complete protective shell 3, specifically, the opening of the upper shell 4 is snapped into the opening of the lower shell 5. In this embodiment, the first circuit board 1 is located above the second circuit board 2. In order to facilitate the connection between the first circuit board 1 and the inner top wall of the upper shell 4, the side of the second circuit board 2 parallel to its extension direction is provided with an avoidance groove, and the avoidance groove extends along the extension direction of the second circuit board 2. When connecting the first circuit board 1 and the inner fixed wall of the upper shell 4, the second circuit board 2 is passed through by passing through the avoidance groove, so that the first circuit board 1 is installed on the inner top wall of the upper shell 4 using bolts for replacement or disassembly.

[0045] In order to increase the connection strength between the upper shell 4 and the lower shell 5, bolt connection columns are provided at the four end corners inside the upper shell 4 and the lower shell 5. The bolt connection columns in the upper shell 4 and the bolt connection columns in the lower shell 5 have the same cross-sectional dimensions, and the height is equal to the inner cavity height of the protective shell 3; the protective shell 3 also includes bolts arranged from bottom to top; the head of the bolt is located in the bolt connection column of the lower shell 5, and the tail of the bolt is threadedly connected to the bolt connection column of the upper shell 4. In this embodiment, the bolt is a cross screw, and a countersunk hole is provided on the lower surface of the bolt connection column of the lower shell 5. The head of the cross screw is accommodated in the countersunk hole, and the threaded portion of the cross screw is threadedly connected to the bolt connection column of the lower shell 5 and the bolt connection column of the upper shell 4. The connection force provided by the cross screw is determined according to actual construction requirements.

[0046] The top opening of the upper housing 4 has a receiving opening for receiving the display 6. The display 6 is received in the receiving opening. In this embodiment, the display 6 can be a LED display screen.

[0047] The bridge circuit includes a strain gauge terminal 7; a terminal receiving hole is provided on the side wall of one end of the upper housing 4; and the strain gauge terminal 7 is embedded in the terminal receiving hole. In this embodiment, the strain gauge is pasted or installed on the object to be measured, and when the object to be measured vibrates, the strain gauge generates a variable output current, which is input into the bridge circuit through the strain gauge terminal 7.

[0048] An operation and observation port is provided on the side wall of the other end of the upper shell 4. Figure 5As shown. In this embodiment, a zero adjustment button 8 and a bridge setting switch 9 are provided on the side of the first circuit board 1 facing the operation and observation port, which are used together to adjust the single-arm, half-bridge, and full-bridge measurement modes of the bridge circuit. The construction personnel operate the zero adjustment button 8 and the bridge setting switch 9 through the operation and observation port; at the same time, a charging port 10 and a power indicator light 11 are provided on the side of the battery 13 facing the operation and observation port, and the construction personnel charge the battery 13 and view the status of the power indicator light through the operation and observation port. In this embodiment, a vertical mounting plate extends from the first circuit board 1 toward the operation and observation port, and the zero adjustment button 8 and the bridge setting switch 9 are installed on the mounting plate, and the zero adjustment button 8 and the bridge setting switch 9 are electrically or mechanically connected to the bridge circuit.

[0049] The upper cover of the operation and observation port is provided with a cover plate 12. In this embodiment, the cover plate 12 includes an elastic <-shaped piece, a rectangular main body plate and two strip-shaped protrusions which are integrally arranged from top to bottom, wherein the deformation direction of the elastic <-shaped piece is the vertical direction, and a baffle in the vertical direction is arranged on the upper side of the elastic <-shaped piece, and two strip-shaped grooves adapted to the strip-shaped protrusions are provided on the lower side of the operation and observation port. When the cover plate 12 is installed on the operation and observation port, the strip-shaped protrusion is first installed in the strip-shaped groove, and then the baffle on the upper side of the elastic <-shaped piece is pressed to deform the elastic <-shaped piece in the vertical direction, so that the rectangular main body plate and the elastic <-shaped piece can be accommodated in the operation and observation port, and then the baffle on the upper side of the elastic <-shaped piece is released, at which time the upper side of the elastic <-shaped piece is pressed against the upper side surface of the operation and observation port, and the baffle on the upper side of the elastic <-shaped piece is parallel to the outer side surface of the end of the upper shell 4. Alternatively, the cover plate 12 may be a plate with a longitudinal cross-section larger than the operation and observation opening, and may be mounted on the outside of the operation and observation opening by bolts.

[0050] Embodiment 2:

[0051] The present application also provides a micro-bridge adjustable dynamic strain measurement system, such as Fig. 9 As shown, it includes: MCU control module, bridge circuit, signal conditioning circuit, display, SD card, analog-to-digital converter and power supply circuit;

[0052] The bridge circuit, the signal conditioning circuit, the analog-to-digital converter and the MCU control module are connected in sequence;

[0053] The display is connected to the MCU control module;

[0054] The power supply circuit is respectively connected with the bridge circuit, the signal conditioning circuit, the analog-to-digital converter, the MCU control module and the display;

[0055] The strain amount is measured by switching the bridge connection mode through the bridge circuit, and the strain amount is converted into an electrical signal and transmitted to the signal conditioning circuit. The signal conditioning circuit processes the electrical signal, and the analog-to-digital converter converts the processed electrical signal into a digital signal, and the digital signal is transmitted to the MCU control module. The MCU control module processes the digital signal and then transmits it to the display and SD card.

[0056] The functions of each part are introduced below:

[0057] The bridge circuit is used to switch the bridge connection mode, and the switched bridge converts the strain into the change of the resistance value of the strain gauge, and then converts the change of the resistance value of the strain gauge into an electrical signal and transmits it to the signal conditioning circuit;

[0058] Signal conditioning circuit, used to amplify and convert electrical signals into digital signals, and transmit the digital signals to the MCU control module;

[0059] MCU control module, used for receiving digital signals and transmitting them to the display after processing them;

[0060] Display, used to display the data transmitted by the MCU control module;

[0061] The power supply circuit is used to convert the lithium-ion battery voltage into various voltages and to power the bridge circuit module, MCU control module, display and signal conditioning circuit.

[0062] The following is a detailed introduction to each part:

[0063] The utility model relates to a micro-bridge adjustable dynamic micro-strain measurement system which is composed of hardware and software.

[0064] The hardware part adopts a double-layer circuit board design, placing the MCU control module, display, SD card module, etc. on a 36mm*63mm board, and placing the bridge circuit, signal conditioning circuit, power supply circuit, etc. on another board of the same size. The two boards are overlapped and fixed, which improves the system space utilization and occupies a smaller space.

[0065] This part is mainly composed of MCU control module, bridge circuit, signal conditioning circuit, power supply circuit and display.

[0066] The MCU control module is the core part of the embedded system, which is mainly used to manage data and generate control signals; the MCU control module is mainly composed of the main control chip and the minimum system peripheral circuit. The main control chip is the STM32L431 chip developed by ST.

[0067] The minimum system peripheral circuit includes a clock circuit, a reset circuit, an interrupt control circuit, etc. The clock circuit, the reset circuit and the interrupt control circuit are respectively connected to the main control chip.

[0068] The clock circuit provides a unified clock rhythm for the entire system; the reset circuit can restore the system to the starting state when necessary; the interrupt control circuit can process each interrupt signal in real time to improve the working efficiency of the MCU.

[0069] The software development is based on the Keil5 MDK-ARM development environment and is written in C language based on the STM32 library function. The software part mainly includes functions such as data acquisition, data processing and data storage, and the implementation of the functions is as described above. Data acquisition mainly collects strain data with the set sampling frequency, sampling interval and sampling time. Data processing uses FIR digital filters to filter the collected strain data, eliminate the interference of environmental noise as much as possible, reduce measurement errors, and perform data calculations based on relevant theoretical formulas of strain. The data storage part uses the FATFS file management system, which can store the collected strain data in a 128G memory card.

[0070] The software development of this system is based on the Keil5 MDK-ARM development environment and is written in C language based on the STM32 library functions.

[0071] The bridge circuit is used to convert the resistance change of the resistance strain gauge into a voltage output for subsequent data collection; the bridge circuit module uses a dip switch to switch the bridge connection mode. The staff can manually adjust the opening and closing of the dip switch (J11, J12) to select single-arm, half-bridge and full-bridge. The figure below is a schematic diagram of the bridge circuit switching.

[0072] The schematic diagram of the bridge circuit switching bridge mode is as follows Figure 6 As shown, P11 is the strain gauge terminal. When the single-arm bridge mode is adopted, the staff adjusts the dip switch to close the two switches J11 and J12, and connects a single strain gauge to the 2 and 3 pins of P11; when the half-bridge mode is adopted, the staff adjusts the dip switch to connect the two strain gauges to the 1 and 3 and 2 and 3 pins of P11 respectively, disconnects the J11 switch at the same time, and closes the J12 switch; when the full-bridge mode is adopted, the four strain gauges are directly connected to the circuit, and the two switches J11 and J12 are disconnected at the same time.

[0073] The signal conditioning circuit is mainly used to amplify and filter the analog voltage signal to make it suitable for the input of the ADC; the signal conditioning circuit is mainly composed of an amplifier circuit, a filter circuit and a clamp circuit. The utility model adopts the programmable instrument amplifier LTC6915 to form an amplifier circuit, which is mainly used to amplify the voltage signal output by the bridge to meet the voltage range entering the ADC. The filter circuit adopts a first-order RC low-pass filter with a cut-off frequency of 150Hz, which can filter the voltage signal output by the amplifier circuit to reduce the influence of environmental noise; the clamp circuit can limit the filtered voltage signal to between 0-3V to avoid damaging the ADC. The structural block diagram of the signal conditioning circuit is shown as follows Figure 7 shown.

[0074] like Figure 8 As shown in the figure, the power supply circuit converts the lithium battery voltage into the power supply voltage required by each chip; the power supply circuit includes a charge and discharge management circuit and a power supply voltage circuit. The charge and discharge management circuit mainly manages the charge and discharge and protects the battery, and the power supply voltage circuit mainly provides the various voltages required by the system.

[0075] The lithium battery of the utility model provides power for the entire system; the lithium battery charge and discharge management circuit adopts the ETA9741 chip, which manages the charge and discharge of the lithium battery and outputs +5V voltage; it is mainly responsible for identifying the system power supply amplitude, generating corresponding short-moment waves, and driving the subsequent circuit to output power. The battery protection circuit adopts the XB4908 chip, which has all the protection functions required in battery applications, including overcharge, overcurrent, overdischarge and load short-circuit protection.

[0076] The ADP5071 chip converts the +5V voltage generated by ETA9741 into +5V. The quality of the +5V voltage generated at this time is poor and the error is large when directly applied, so it needs to be converted into two voltage outputs of +-6V first; the first ADP7142 chip reduces +6V to +5V; the second ADP7142 reduces +5V to +3V; ADP7182 reduces -6V to -3V; and the REF2030 chip generates a reference voltage of +5V.

[0077] The power supply voltage circuit mainly includes a bridge excitation voltage, a PGIA power supply voltage and a reference voltage. The bridge excitation voltage is connected to the bridge circuit module; the PGIA power supply voltage is connected to the amplifier circuit; and the reference voltage is connected to the amplifier circuit.

[0078] The bridge excitation voltage (+5V) is mainly used to power the bridge circuit; the PGIA power supply voltage (+-3V) is mainly used to provide dual power supply for the programmable gain instrumentation amplifier; the reference voltage (+1.5V) is mainly used to raise the negative voltage signal to be collected so as to meet the voltage range (0-3V) entering the ADC. The bridge excitation voltage and PGIA dual power supply voltage are obtained from different versions of ADP7182 and ADP7142 respectively, and the reference voltage is obtained through the REF2030 chip. The power supply circuit diagram is shown in the figure below. Figure 8 shown.

[0079] The display is used to display some necessary information, such as strain value, bridge connection mode, remaining capacity of SD card, etc., so that the staff can clearly know the working status of the system; the SD card is used to store the system's data for subsequent viewing by the staff.

[0080] The overall design of the hardware part of the micro-bridge adjustable dynamic micro-strain measurement system involved in the utility model is as follows: Fig. 9 shown.

[0081] The strain gauge uses a standard 120 ohm strain gauge to measure the dynamic strain of structural vibration. The Wheatstone bridge circuit can be freely switched between single-arm, half-bridge and full-bridge by adjusting the dip switch.

[0082] The signal conditioning circuit is mainly used to amplify and filter the weak voltage signal output by the bridge circuit and raise the voltage to a signal range that meets the input of the analog-to-digital converter (ADC).

[0083] The MCU mainly controls peripherals such as ADC, LCD, SD card, etc. and performs calculations on strain values.

[0084] After the system is powered on, the MCU performs device initialization, including peripheral initialization and clock initialization. Then the bridge mode is selected and strain zeroing is performed. After zeroing, the strain acquisition mode is entered. The STM32 controls the ADC to collect data according to the sampling frequency, sampling interval and sampling time. When the data acquisition is completed, the DMA directly transmits the data, and the MCU processes and calculates the collected voltage data. Finally, the strain measurement results are displayed on the LCD screen, and the strain measurement data is stored in the SD card.

[0085] The operation part of this system is concentrated on the side of the system, and you only need to operate the dip switches and buttons.

[0086] The 1st and 2nd switches of the DIP switch are the bridge setting switches for channel 1, the 3rd and 4th switches are the bridge setting switches for channel 2, and the 5th switch is the power switch. When the single-arm measurement mode is selected, switches 1, 2, 3, and 4 need to be turned on; when the half-bridge measurement mode is selected, switches 2 and 3 are turned on and switches 1 and 4 are turned off; when the full-bridge measurement mode is selected, switches 1, 2, 3, and 4 can all be turned off.

[0087] The zero adjustment button has two functions: one is a short press to select single-arm, half-bridge, or full-bridge measurement mode; the other is a long press to perform strain zero adjustment.

[0088] The operation process of this system: After the system is powered on and preheated, connect the strain gauge to the system interface through the terminal block in the corresponding connection method. Then set the hardware bridge measurement circuit according to the established method through the dip switch, and at the same time, switch the system's measurement mode to the corresponding bridge circuit mode through the button. When you are ready to start measuring, you first need to press and hold the zero adjustment button to zero the strain. After zeroing is completed, the system enters the normal working mode. During the measurement process, you can view relevant information such as time, strain value, remaining capacity of the SD card, etc. on the LCD display, and you can view historical measurement data in the SD card.

[0089] Embodiment 3:

[0090] The utility model is used to measure the strain of the cantilever beam when it is bent by using the micro-bridge adjustable dynamic micro-strain measurement system.

[0091] At room temperature, first paste the strain gauge on the cantilever beam of the vibration test bench, and then connect the strain gauge to the system interface. After the equipment is initialized and the strain is zeroed, start measuring the strain of the cantilever beam. Apply a concentrated load to the free end of the cantilever beam to bend it to the specified position, and record the data measured by the system and the standard strain tester.

[0092] Three bridge connection modes, namely single arm, half bridge and full bridge, were used respectively. The free end of the cantilever beam was bent to three different positions according to the above measurement method. The measurement results are shown in Table 1.

[0093] Table 1 Measured data results

[0094]

[0095] Obviously, the described embodiments are only some embodiments of the utility model, but not all embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0096] The above are merely embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application are included in the scope of the claims of the present application.

Claims

1. A miniature bridge adjustable dynamic strain measuring device, characterized in that: Includes a double-layer circuit board; The double-layer circuit board comprises a first circuit board (1) for mounting an MCU control module, a display (6) and an SD card, and a second circuit board (2) for mounting a bridge circuit, a signal conditioning circuit and a power supply circuit; The first circuit board (1) and the second circuit board (2) are both rectangular, arranged in parallel, and fixedly connected.

2. The device according to claim 1, characterized in that The first circuit board (1) and the second circuit board (2) are both arranged in a horizontal direction; The MCU control module, the SD card, the bridge circuit, the signal conditioning circuit and the power supply circuit are located between the first circuit board (1) and the second circuit board (2); The display (6) is mounted on the upper side of the first circuit board (1).

3. The device according to claim 2, characterized in that The device also includes a rectangular protective shell (3) extending in the horizontal direction; The first circuit board (1) is mounted on the top wall of the protective housing (3).

4. The device according to claim 3, characterized in that The protective shell (3) comprises an upper shell (4) located on the upper side and a lower shell (5) located on the lower side; The upper shell (4) and the lower shell (5) are both provided with openings; The opening of the upper shell (4) is located on the lower side of the upper shell (4); The opening of the lower shell (5) is located on the upper side of the lower shell (5); The opening of the upper shell (4) is snap-fitted with the opening of the lower shell (5) to form a complete protective shell (3).

5. The device according to claim 4, characterized in that Bolt connection columns are provided at the four inner corners of the upper shell (4) and the lower shell (5); The protective shell (3) also includes bolts arranged from bottom to top; The head of the bolt is located in the bolt connection column of the lower shell (5), and the tail of the bolt is threadedly connected in the bolt connection column of the upper shell (4).

6. The device according to claim 4, characterized in that The top opening of the upper housing (4) has a receiving opening for receiving the display (6); The display (6) is accommodated in the accommodation opening.

7. The device according to claim 4, characterized in that The bridge circuit comprises a strain gauge terminal (7); A terminal receiving hole is provided on a side wall of one end portion of the upper housing (4); The strain gauge connecting terminal (7) is embedded in the connecting terminal accommodating hole.

8. The device according to claim 4, characterized in that An operation and observation port is provided on the side wall of one end of the upper shell (4).

9. The device according to claim 8, characterized in that The operation and observation port is covered with a cover plate (12).

10. The device according to claim 2, characterized in that A battery (13) is installed on the lower side of the second circuit board (2).

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