CN112615617A - Signal conditioner for shock stress wave system - Google Patents

Abstract

The invention discloses a signal conditioner for an impact stress wave system, comprising a power supply module, a constant current source module, a signal amplification module and a filter module; the power supply module converts the input voltage into the voltage required by the system and is a constant current source Module, signal amplification module and filter module supply power; constant current source module, connected to the acceleration sensor, provides constant current to the acceleration sensor, and transmits the measured voltage value to the signal amplification module; signal amplification module, connects the constant current source module with the The filtering module amplifies the voltage signal measured by the constant current source module, and transmits the amplified signal to the filtering module; Data acquisition card. The invention realizes that the system noise is reduced while the power supply with strong noise is supplied, and the accuracy and robustness of the system measurement are improved.

Description

A Signal Conditioner for Shock Stress Wave Systems

technical field

The invention belongs to the technical field of non-destructive testing, and more particularly relates to a signal conditioner for an impact stress wave system.

Background technique

Concrete structures have the characteristics of high strength and high rigidity and are widely used in various structures. However, due to various factors such as construction and personnel, various quality defects of concrete frequently occur, which in turn leads to insufficient concrete height and even affects the safety performance of buildings. , so as to threaten the safety of people's lives and property. Therefore, the detection of concrete defects is an important approach for concrete quality assessment and safety diagnosis, and is of great significance for maintaining social and economic stability.

The traditional core drilling method causes local damage to the structural concrete, and it is not suitable to use the core drilling method when the concrete strength grade is low. Concrete non-destructive testing technology detects the defect information in concrete without damaging or affecting the concrete. It is the main technology of on-site engineering testing in recent years. The shock stress wave method has the advantages of simple operation and high accuracy, and has been widely used in non-destructive testing of concrete.

The signal conditioner is directly connected to the external measurement sensor in the shock stress wave detection system. The electronic noise in the signal conditioner directly affects the detection accuracy and precision of the system. Therefore, reducing the electronic noise is an important way to improve the measurement accuracy of the system. One of the main sources of electronic noise is the power supply voltage ripple. At present, the common practice is to increase the capacitance of the power supply to eliminate the power supply voltage ripple. However, the realization of large-capacity capacitors in circuit design will occupy most of the circuit area, and the large-capacity capacitors Large fluctuations in parameters will increase the instability of the system. Another method is to use a battery with a smaller voltage ripple, but the battery will not only increase the system volume, but also make the system application less flexible, limiting the system working time.

Therefore, how to provide a signal conditioner for an impact stress wave system is an urgent problem to be solved by those skilled in the art.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a signal conditioner for an impact stress wave system, which can reduce system noise and improve the accuracy and robustness of system measurement while supplying a power supply with strong noise.

In order to achieve the above object, the present invention adopts the following technical solutions:

A signal conditioner for an impact stress wave system, comprising: a power supply module, a constant current source module, a signal amplification module and a filter module; wherein,

The power supply module is used to convert the input voltage into the voltage required by the system, and supply power to the constant current source module, the signal amplification module and the filter module;

The constant current source module is connected to the connected acceleration sensor for providing constant current to the acceleration sensor and transmitting the measured voltage value to the signal amplifying module;

The signal amplification module is connected to the constant current source module and the filter module, amplifies the voltage signal measured by the constant current source module, and transmits the amplified signal to the filter module;

The filtering module is connected to the signal amplifying module, converts the amplified signal into a signal voltage by removing the bottom current, and transmits the signal voltage to the data acquisition card.

Preferably, the power module includes: a boosting circuit, a noise reduction circuit and a voltage stabilizing circuit; wherein,

The booster circuit is connected to an external power supply interface for increasing the input low voltage value;

The noise reduction circuit is connected to the booster circuit for eliminating voltage ripple, reducing system noise and improving the accuracy of system measurement;

The voltage stabilizing circuit is connected to the noise reduction circuit for stabilizing the voltage at a fixed value.

Preferably, the boost circuit includes: a DC-DC converter U0, an input capacitor C1, an output capacitor C2, a voltage adjustment resistor R1 and a voltage adjustment resistor R2;

The input capacitor C1 is directly connected to the external power supply, and is used to reduce the influence of the AC signal in the power supply on the circuit;

The DC-DC converter U0 is connected to the input capacitor C1 for amplifying the input voltage;

The output capacitor C2 is connected to the output end of the DC-DC converter U0 to reduce the influence of the voltage ripple on the circuit;

The voltage adjusting resistor R1 and the voltage adjusting resistor R2 are connected to the output terminal of the DC-DC converter U0 for adjusting the output voltage value.

Preferably, the noise reduction circuit includes: a transistor Q1, a resistor R3 and a capacitor C3;

The collector of the transistor Q1 is connected to the output of the booster circuit, and is used to amplify the smaller capacitor C3 to eliminate the voltage ripple;

The resistor R3 is connected to the emitter and the base of the triode Q1, and is used to maintain the emitter junction current of the triode in the amplification range;

The capacitor C3 is connected to the transistor Q1 and the ground for eliminating voltage ripple.

Preferably, the voltage regulator circuit includes: an integrated voltage regulator block U1, a voltage regulator resistor R4 and a voltage regulator resistor R5; the input end of the integrated voltage regulator block U1 is connected to the output of the noise reduction circuit, and the integrated voltage regulator block U1 The voltage regulating end of the 2 is connected to the voltage regulating resistor R4 and the voltage regulating resistor R5; the voltage regulating resistor R4 and the voltage regulating resistor R5 are connected in series to the output end of the integrated voltage stabilizing block U1 and the ground.

Preferably, the constant current source module includes: a voltage reference, a differential amplifier U2, an operational amplifier U3 and an output adjustment resistor R7; two input ends of the differential amplifier U2 are connected to the voltage reference; The output terminal is connected to one input terminal and the reference terminal of the differential amplifier U2, and the other input terminal is connected to the output adjustment resistor R7 and then connected to the output terminal and the measurement terminal of the differential amplifier U2; the operational amplifier U3 is connected to the output adjustment resistor. The connection point of R7 is the output end of the constant current source, and the output end of the constant current source is connected with the acceleration sensor.

Preferably, the voltage includes: a micro-power consumption voltage reference tube D1 and a current limiting resistor R6; the micro-power consumption voltage reference tube D1 and the current limiting resistor R6 are connected in series with the output of the power module.

Preferably, the signal amplification module includes: a filter resistor R8, a filter capacitor C4, an operational amplifier U4, an operational amplifier U5, a gain adjustment resistor R9, a gain adjustment resistor R10 and a gain selection switch K1; the operational amplifier U4 and the operational amplifier U5 The power supply is connected to the output terminal of the power supply module, the non-inverting input terminal of the operational amplifier U4 is connected to the non-inverting input terminal of the operational amplifier U5 through the resistor R8, and the output terminal of the operational amplifier U4 is connected to the operational amplifier U5 through the gain adjustment resistor R9 and the gain adjustment resistor R10. The output terminal is connected; the gain adjustment resistor R9 is connected to the inverting input terminal and the output terminal of the operational amplifier U4; the inverting input terminal and the output terminal of the operational amplifier U5 are connected to the gain adjustment resistor R10 after being connected; the filter capacitor C4 The non-inverting input terminal of U4 of the operational amplifier is connected to the ground; the gain selection switch K1 is connected in parallel with the gain adjustment resistor R9; the input terminal of the operational amplifier U4 is connected to the output terminal of the constant current source, and the output terminal of the operational amplifier U4 is the amplified signal.

Preferably, the filter module includes: a coupling capacitor C5 and a resistor R11; the coupling capacitor C5 is connected to the output end of the operational amplifier U4 and the resistor R11; the coupling capacitor C5 is connected to the resistor R11 and then connected to an external data acquisition card; data acquisition After the card digitally converts the measurement signal, it is connected to the host computer through a USB cable.

The beneficial effects of the present invention are:

The invention eliminates the voltage ripple of the power supply through the noise reduction circuit, realizes the power supply with strong noise, reduces the influence of the system noise on the detection result, and improves the accuracy and robustness of the system measurement. In addition, the adopted noise reduction circuit avoids the problem of increasing the circuit area caused by increasing the capacitance capacity, reduces the volume of the system, and has the characteristics of miniaturization as a whole; - DC converters, micro-power differential amplifiers, operational amplifiers and other low-power components, the overall system design has the advantages of low power consumption and high power efficiency; The size of the output adjustment resistor in the voltage circuit enables the output voltage of the power module to meet the requirements of other circuits, therefore, the present invention also has high flexibility.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Figure 1 is a schematic structural diagram of the present invention.

Among them, in the figure:

1-power module; 2-constant current source module; 3-signal amplification module; 4-filter module; 5-acceleration sensor; 6-data acquisition card; 7-host computer; 8-USB connection; 11-boost circuit ; 12- noise reduction circuit; 13- voltage regulator circuit; 21- voltage reference.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to FIG. 1, the present invention provides a signal conditioner for an impact stress wave system, including: a power module 1, a constant current source module 2, a signal amplification module 3 and a filter module 4; wherein,

The power supply module 1 is used to convert the input voltage into the voltage required by the system, and supply power to the constant current source module 2, the signal amplification module 3 and the filter module 4;

The constant current source module 2 is connected to the connected acceleration sensor 5 for providing a constant current to the acceleration sensor 5 and transmitting the measured voltage value to the signal amplifying module 3;

The signal amplification module 3 is connected to the constant current source module 2 and the filter module 4, amplifies the voltage signal measured by the constant current source module 2, and transmits the amplified signal to the filter module 4;

The filtering module 4 is connected to the signal amplifying module 3 , and converts the amplified signal to a signal voltage by removing the bottom current, and transmits the signal voltage to the data acquisition card 6 .

In this embodiment, the power supply module 1 includes: a boosting circuit 11, a noise reduction circuit 12 and a voltage stabilizing circuit 13; wherein,

The booster circuit 11 is connected to an external power supply interface for increasing the input low voltage value;

The noise reduction circuit 12 is connected to the boost circuit 11, and is used for eliminating voltage ripple, reducing system noise and improving the accuracy of system measurement;

The voltage regulator circuit 13 is connected to the noise reduction circuit 12, and is used for stabilizing the voltage at a fixed value.

In this embodiment, the boost circuit 11 includes: a DC-DC converter U0, an input capacitor C1, an output capacitor C2, a voltage adjustment resistor R1 and a voltage adjustment resistor R2; the input capacitor C1 is connected to the external power supply V1; the DC-DC converter The input terminal of U0 is connected in parallel with the input capacitor C1; the voltage adjustment resistors R1 and R2 are connected in parallel with the output capacitor C2 after being connected in series, and are connected in parallel with the output terminal of the DC-DC converter U0; the input capacitor C1 is directly connected to the external power supply to reduce the power supply The influence of the AC signal on the circuit; the DC-DC converter U0 is connected to the input capacitor C1 to amplify the input voltage, and the voltage amplification factor is related to the value of the voltage adjustment resistor R1 and the voltage adjustment resistor R2; the output capacitor C2 , connected to the output terminal of the DC-DC converter U0 to reduce the influence of voltage ripple on the circuit; the voltage adjustment resistor R1 and the voltage adjustment resistor R2 are connected to the output terminal of the DC-DC converter U0 to adjust the output voltage value.

In this embodiment, the noise reduction circuit 12 includes: a transistor Q1, a resistor R3 and a capacitor C3; the current limiting resistor R3 is connected to the collector and base of the transistor Q1 and is connected to the output of the boost circuit 1111; the noise reduction capacitor C3 is connected to the transistor The base of Q1 and the ground; the collector of the transistor Q1 is connected to the output of the booster circuit 11, which is used to amplify the smaller capacitor C3 to eliminate the voltage ripple; the resistor R3 is connected to the emitter and the base of the transistor Q1, used for The emitter junction current of the triode is maintained in the amplification range; the capacitor C3 is connected to the triode Q1 and the ground to eliminate the voltage ripple.

In this embodiment, the voltage regulator circuit 13 includes: an integrated voltage regulator block U1, a voltage regulator resistor R4 and a voltage regulator resistor R5; the input end of the integrated voltage regulator block U1 is connected to the output of the noise reduction circuit 12, and the voltage of the integrated voltage regulator block U1 is connected to the output of the noise reduction circuit 12. The adjusting end is connected to the voltage adjusting resistor R4 and the voltage adjusting resistor R5; the voltage adjusting resistor R4 and the voltage adjusting resistor R5 are connected in series and then connected to the output end of the integrated voltage stabilizer block U1 and the ground. The integrated voltage stabilizing block U1 is connected to the noise reduction circuit 12 and functions as an integrated three-stage voltage stabilizing block with variable output voltage, which is obtained by adjusting the voltage regulating resistors R4 and R5; the voltage regulating resistor R4 and the voltage regulating resistor R5 are connected to the integrated The voltage-stabilizing block U1 can adjust the value of the output voltage by adjusting the ratio of the voltage-regulating resistor R4 to the voltage-regulating resistor R5.

In this embodiment, the power supply efficiency of the power supply module 1 is high, and different power supply voltage values can be applied. The output voltage value of the power supply module 1 can be adjusted through the voltage adjustment resistor R1 and the voltage adjustment resistor R2, or the voltage adjustment resistor R4 and the voltage adjustment resistor. resistor R5 to achieve.

In this embodiment, the constant current source module 2 includes: a voltage reference 21 , a differential amplifier U2 , an operational amplifier U3 and an output adjustment resistor R7 . The voltage includes: the micro-power voltage reference 21 tube D1 and the current limiting resistor R6; the micro-power voltage reference 21 tube D1 and the current limiting resistor R6 are connected in series with the output of the power module 1 . The two input terminals of the differential amplifier U2 are connected in parallel with the micro-power voltage reference 21 tube D1; the output terminal of the operational amplifier U3 is connected to one input terminal and to the reference terminal of the differential amplifier U2, and the other input terminal is connected to the output adjustment resistor R7. It is connected with the output end and the measurement end of the differential amplifier U2; the connection point between the operational amplifier U3 and the output adjustment resistor R7 is the output end of the constant current source, and the output end of the constant current source is connected with the acceleration sensor 5, the current is marked as I _sen , the voltage The size is recorded as V _sen . The voltage reference 21 is connected to the output of the power supply module 1 to obtain a stable voltage value _ui to the differential amplifier to obtain the desired constant current source value. The differential amplifier and the operational amplifier, as shown in Figure 1, form the core part of the constant current source, so that the output of the constant current source is constant and does not change with the change of the load impedance. The output current I _sen of the constant current source is related to the input voltage value u _i is related to the output adjustment resistor R7.

In this embodiment, the current value output by the constant current source module 2 is adjustable, and the value is equal to the ratio of the voltage input by the differential amplifier U2 to the output adjustment resistor R7. Therefore, the output value of the current source can be adjusted by changing the size of the output adjustment resistor R7. current size.

In this embodiment, the signal amplification module 3 includes: a filter resistor R8, a filter capacitor C4, an operational amplifier U4, an operational amplifier U5, a gain adjustment resistor R9, a gain adjustment resistor R10, and a gain selection switch K1; The power supply is connected to the output terminal of the power supply module 1, the non-inverting input terminal of the operational amplifier U4 is connected to the non-inverting input terminal of the operational amplifier U5 through the resistor R8, and the output terminal of the operational amplifier U4 is connected to the operational amplifier U5 through the gain adjustment resistor R9 and the gain adjustment resistor R10. The output terminal is connected; the gain adjusting resistor R9 is connected to the inverting input terminal and the output terminal of the operational amplifier U4; the inverting input terminal and the output terminal of the operational amplifier U5 are connected to the gain adjusting resistor R10 after being connected; The non-inverting input terminal and the ground; the gain selection switch K1 is connected in parallel with the gain adjustment resistor R9; the input terminal of the operational amplifier U4 is connected to the output terminal of the constant current source, and the output terminal of the operational amplifier U4 is the amplified signal. The filter resistor R8 and the filter capacitor C4 are connected to the operational amplifier U5 to form a low-pass filter circuit; the operational amplifier U4 is connected to the low-pass filter circuit formed by the filter resistor R8 and the filter capacitor C4 to form a voltage follower for subsequent signal amplification circuits Provide a reference voltage to avoid amplifying the bottom current conversion voltage. The two input ends of the operational amplifier U4 are respectively connected to the output of the constant current source, the filter resistor R8 and the filter capacitor C4 to increase the driving capability of the input signal; the operational amplifier U5 is connected to the filter Resistor R8, filter capacitor C4, and two gain adjustment resistors R9 and R10 are connected to the output end to form a signal amplifier to amplify the measured voltage signal. The gain coefficient is related to the gain adjustment resistor R9 and the gain adjustment resistor R10; the gain selection switch K1, The parallel gain adjustment resistor R9 is used to adjust the gain coefficient of the amplifier circuit to control the gain gear. The amplification factor of the signal amplifier is controlled by the gain selection switch K1. When the gain selection switch K1 is closed, the gain multiple is 1. When the switch is turned off, the gain is greater than 1, and the gain multiple is determined by the ratio of the two gain adjustment resistors.

In this embodiment, the filter module 4 includes: a coupling capacitor C5 and a resistor R11; the coupling capacitor C5 is connected to the output end of the operational amplifier U4 and the resistor R11; the coupling capacitor C5 is connected to the resistor R11 and then connected to the external data acquisition card 6; The card 6 is connected to the host computer 7 through the USB connection 8 after digital conversion of the measurement signal. The coupling capacitor C5 is used to separate the DC signal in the previous stage circuit.

The invention eliminates the voltage ripple of the power supply through the noise reduction circuit, realizes the power supply with strong noise, reduces the influence of the system noise on the detection result, and improves the accuracy and robustness of the system measurement. In addition, the adopted noise reduction circuit avoids the problem of increasing the circuit area caused by increasing the capacitance capacity, reduces the volume of the system, and has the characteristics of miniaturization as a whole; - DC converters, micro-power differential amplifiers, operational amplifiers and other low-power components, the overall system design has the advantages of low power consumption and high power efficiency; The size of the output adjustment resistor in the voltage circuit enables the output voltage of the power module to meet the requirements of other circuits, therefore, the present invention also has high flexibility.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant part can be referred to the description of the method.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A signal conditioner for an impact stress wave system, comprising: a power supply module, a constant current source module, a signal amplification module and a filter module; wherein, The power supply module is used to convert the input voltage into the voltage required by the system, and supply power to the constant current source module, the signal amplification module and the filter module; The constant current source module is connected to the connected acceleration sensor for providing constant current to the acceleration sensor and transmitting the measured voltage value to the signal amplifying module; The signal amplification module is connected to the constant current source module and the filter module, amplifies the voltage signal measured by the constant current source module, and transmits the amplified signal to the filter module; The filtering module is connected to the signal amplifying module, converts the amplified signal into a signal voltage by removing the bottom current, and transmits the signal voltage to the data acquisition card. 2 . The signal conditioner for an impulse stress wave system according to claim 1 , wherein the power module comprises: a booster circuit, a noise reduction circuit and a voltage regulator circuit; wherein, 2 . The booster circuit is connected to an external power supply interface for increasing the input low voltage value; The noise reduction circuit is connected to the booster circuit for eliminating voltage ripple, reducing system noise and improving the accuracy of system measurement; The voltage stabilizing circuit is connected to the noise reduction circuit for stabilizing the voltage at a fixed value. 3. A signal conditioner for an impulse stress wave system according to claim 2, wherein the boost circuit comprises: a DC-DC converter U0, an input capacitor C1, an output capacitor C2, a voltage regulator Resistor R1 and voltage adjustment resistor R2; The input capacitor C1 is directly connected to the external power supply, and is used to reduce the influence of the AC signal in the power supply on the circuit; The DC-DC converter U0 is connected to the input capacitor C1 for amplifying the input voltage; The output capacitor C2 is connected to the output end of the DC-DC converter U0 to reduce the influence of the voltage ripple on the circuit; The voltage adjusting resistor R1 and the voltage adjusting resistor R2 are connected to the output terminal of the DC-DC converter U0 for adjusting the output voltage value. 4. The signal conditioner for the shock stress wave system according to claim 2 or 3, wherein the noise reduction circuit comprises: a transistor Q1, a resistor R3 and a capacitor C3; The collector of the transistor Q1 is connected to the output of the booster circuit, and is used to amplify the smaller capacitor C3 to eliminate the voltage ripple; The resistor R3 is connected to the emitter and the base of the triode Q1, and is used to maintain the emitter junction current of the triode in the amplification range; The capacitor C3 is connected to the transistor Q1 and the ground for eliminating voltage ripple. 5. A signal conditioner for an impulse stress wave system according to claim 2, wherein the voltage regulator circuit comprises: an integrated voltage regulator block U1, a voltage regulator resistor R4 and a voltage regulator resistor R5; the integrated voltage regulator The input end of the voltage stabilizing block U1 is connected to the output of the noise reduction circuit, and the voltage regulating end of the integrated voltage stabilizing block U1 is connected to the voltage regulating resistor R4 and the voltage regulating resistor R5; The voltage regulating resistor R5 is connected in series to the output end of the integrated voltage regulating block U1 and the ground. 6. A signal conditioner for an impact stress wave system according to claim 1, wherein the constant current source module comprises: a voltage reference, a differential amplifier U2, an operational amplifier U3 and an output adjustment resistor R7; The two input terminals of the differential amplifier U2 are connected to the voltage reference; the output terminal of the operational amplifier U3 is connected to one input terminal and to the reference terminal of the differential amplifier U2, and the other input terminal is connected to the output adjustment resistor R7. Then, it is connected with the output end and the measurement end of the differential amplifier U2; the connection point between the operational amplifier U3 and the output adjustment resistor R7 is the output end of the constant current source, and the output end of the constant current source is connected with the acceleration sensor. 7 . The signal conditioner for an impulse stress wave system according to claim 6 , wherein the voltage according to the reference comprises: a micro power consumption voltage reference tube D1 and a current limiting resistor R6 ; the micro power voltage reference tube D1 and a current limiting resistor R6 ; The voltage consumption reference tube D1 is connected in series with the current limiting resistor R6 and then connected to the output of the power supply module. 8. A signal conditioner for an impact stress wave system according to claim 1, wherein the signal amplification module comprises: a filter resistor R8, a filter capacitor C4, an operational amplifier U4, an operational amplifier U5, a gain adjustment resistor R9, gain adjustment resistor R10 and gain selection switch K1; the power supplies of the operational amplifier U4 and the operational amplifier U5 are connected to the output terminal of the power supply module, and the non-inverting input terminal of the operational amplifier U4 is connected to the non-inverting input terminal of the operational amplifier U5 through the resistor R8 connected, the output end of the operational amplifier U4 is connected to the output end of the operational amplifier U5 through the gain adjustment resistor R9 and the gain adjustment resistor R10; the gain adjustment resistor R9 is connected to the inverting input end and the output end of the operational amplifier U4; the operational amplifier The inverting input terminal of U5 is connected to the output terminal and then connected to the gain adjustment resistor R10; the filter capacitor C4 is connected to the non-inverting input terminal of U4 of the operational amplifier and the ground; the gain selection switch K1 is connected in parallel with the gain adjustment resistor R9; the operational amplifier U4 The input end of the U4 is connected to the output end of the constant current source, and the output end of the operational amplifier U4 is the amplified signal. 9 . The signal conditioner for the shock stress wave system according to claim 1 , wherein the filter module comprises: a coupling capacitor C5 and a resistor R11 ; the coupling capacitor C5 is connected to the output of the operational amplifier U4 . The terminal is connected to the resistor R11; the coupling capacitor C5 is connected to the resistor R11 and then connected to the external data acquisition card; the data acquisition card digitally converts the measurement signal and connects it to the host computer through a USB connection.

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