High-precision signal conditioning sampling circuit applied to strain sensor

Abstract

The invention discloses a high-precision signal conditioning sampling circuit applied to a strain sensor, and the circuit is characterized in that a high-precision reference voltage source module is connected with a positive power supply and the strain sensor, and provides constant-voltage excitation for the strain sensor; the input end of the charge pump module is connected with a positive power supply and is converted into a negative power supply for output; the signal input end of the signal amplification module is connected with the strain sensor, and the signal amplification module is connected with a positive power supply and a negative power supply output by the charge pump module and is used for amplifying differential signals in a dual-power supply environment; the second-order filtering module is connected with the output end of the signal amplification module to filter noise signals; the A / D conversion module is connected with the output end of the second-order filtering module and converts analog signals into digital signals. A dual-power-supply environment is constructed through the charge pump module, so that the signal amplification module can work under a real dual-power-supply rail. And the problem of'zero dead zone 'or nonlinear distortion caused by common output swing limitation of a single-power operational amplifier is thoroughly eliminated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of signal processing, and particularly relates to a high-precision signal conditioning sampling circuit applied to a strain sensor. BACKGROUND

[0002] The strain sensor is widely applied to the measurement of mechanical quantities in the fields of industrial measurement, medical equipment and aerospace due to its simple structure and stable performance. However, in actual application, the traditional signal conditioning sampling circuit often faces many challenges when processing the weak signals output by the strain sensor.

[0003] Firstly, the output signal of the strain sensor is usually in the order of millivolts or even smaller, and is extremely susceptible to external electromagnetic interference and power frequency noise, resulting in low signal-to-noise ratio and difficult-to-ensure measurement accuracy. Secondly, the existing circuit lacks efficient anti-interference design, and is mostly powered by a single power supply. Limited by the output swing of the operational amplifier, it cannot output a true zero level, resulting in a measurement blind area or nonlinear distortion at near zero, which affects the accuracy of small signal acquisition. In addition, the existing high-precision conditioning circuit is complex in design, large in size and high in power consumption, and is difficult to meet the application requirements of small size and low power consumption of portable devices.

[0004] Therefore, it is urgent to develop a high-precision, low-noise, good linearity and stable and reliable signal conditioning sampling circuit to improve the measurement performance of the strain sensor. SUMMARY

[0005] Therefore, the application provides a high-precision signal conditioning sampling circuit applied to a strain sensor, which completely solves the zero dead zone problem in weak signal acquisition and greatly improves the signal-to-noise ratio of the system by constructing a double power supply environment with high voltage excitation.

[0006] The technical scheme adopted by the application is: a high-precision signal conditioning sampling circuit applied to a strain sensor, characterized by comprising a high-precision reference voltage source module, a charge pump module, a signal amplification module, a second-order filter module and an A / D conversion module.

[0007] The input end of the high-precision reference voltage source module is connected to a positive power supply, and the output end is connected to the power input end of the strain sensor, for providing constant voltage excitation for the strain sensor.

[0008] The input end of the charge pump module is connected to the positive power supply, for converting the positive power supply into a negative power supply output, so as to construct a double power supply environment together with the positive power supply.

[0009] The signal input terminal of the signal amplification module is connected to the differential signal output terminal of the strain gauge sensor, and the power supply terminal of the signal amplification module is connected to the positive power supply and the negative power supply output by the charge pump module, respectively, for amplifying the differential signal in a dual power supply environment.

[0010] The second-order filtering module is connected to the output of the signal amplification module and is used to filter out noise signals;

[0011] The A / D conversion module is connected to the output of the second-order filter module and is used to convert analog signals into digital signals.

[0012] Furthermore, the high-precision reference voltage source module includes a high-precision reference chip U2; the power input terminal of the high-precision reference chip is connected to the system positive power supply through an input resistor R5, and the output terminal outputs a constant voltage of 10V as the constant voltage excitation; the voltage output terminal is connected to the strain gauge sensor through an output resistor R8, and a filter capacitor C13 is connected in parallel to ground at the voltage output terminal.

[0013] Furthermore, the charge pump module includes a reverse charge pump chip U5 and a flying capacitor C14; the input terminal of the reverse charge pump chip U5 is connected to the system positive power supply, and the flying capacitor C14 is connected between the positive and negative terminals of the flying capacitor of the reverse charge pump chip U5; the negative voltage output by the output terminal of the reverse charge pump chip U5 has the same amplitude but opposite polarity as the system positive power supply voltage, and the negative voltage serves as a negative power supply to provide negative rail power to the signal amplification module.

[0014] Furthermore, the signal amplification module includes an instrumentation amplifier U9 and a bias voltage generation circuit;

[0015] The instrumentation amplifier U9 is powered by a dual power supply. Its positive power supply terminal is connected to the system's positive power supply, and its negative power supply terminal is connected to the negative power supply generated by the charge pump module.

[0016] The bias voltage generation circuit is used to generate a DC bias voltage and connect it to the reference voltage input terminal of the instrumentation amplifier U9 to raise the zero-point potential of the output signal of the instrumentation amplifier U9 to the positive voltage range.

[0017] Furthermore, the bias voltage generation circuit includes a first reference voltage source U1 and an operational amplifier U8B; the first reference voltage source generates a first reference voltage, the voltage value of which is half of the reference voltage value of the A / D conversion module, and is connected to the non-inverting input terminal of the operational amplifier; the inverting input terminal and the output terminal of the operational amplifier are shorted to form a voltage follower; the output terminal of the operational amplifier is connected to the reference voltage input terminal of the instrumentation amplifier U9 to match the signal input range of the A / D conversion module.

[0018] Furthermore, the signal input terminal of the signal amplification module is also provided with a hybrid filtering network; the hybrid filtering network includes differential mode filter capacitors C40 and C41 connected across the positive and negative input terminals of the differential signal, and common mode filter capacitors C29 and C43 respectively connected between the differential signal input terminal and ground.

[0019] Furthermore, the second-order filtering module includes a second-order low-pass filter circuit composed of an operational amplifier U8A; the operational amplifier U8A is powered by the same dual power supply as the signal amplification module; the cutoff frequency of the second-order low-pass filter circuit is configured to filter out power frequency interference and high-frequency noise.

[0020] Furthermore, the A / D conversion module includes a 24-bit A / D converter U10 and an external independent reference source; the external reference voltage input terminal of the A / D converter U10 is connected to a second reference voltage generated by a second reference voltage source; the A / D converter U10 has a positive input terminal and a negative input terminal for differential sampling; the common-mode filter capacitor C44 is connected between the signal input line of the positive input terminal and ground; the differential filter capacitor C46 is connected across the positive input terminal and the negative input terminal.

[0021] The beneficial effects of this invention are as follows: This invention constructs a ±12.6V dual-power supply environment through a charge pump module, enabling the signal amplification module to operate under true dual-power rail conditions. Compared to traditional single-power supply circuits, this design ensures that the operational amplifier remains in its optimal linear operating region when processing weak signals close to 0V, completely eliminating the "zero-point dead zone" or nonlinear distortion problems commonly caused by the output swing limitation of single-power supply operational amplifiers. Actual measurement data shows that under 0Nm no-load conditions, the range of the AD sampling values ​​is only 1.3, proving that the system has extremely high stability and linearity near zero. This invention utilizes a high-precision reference voltage source to provide a 10V high-voltage constant-voltage excitation to the sensor, increasing the effective millivolt-level signal amplitude of the strain gauge sensor output by 2-3 times. This directly improves the signal-to-noise ratio at the signal source, and combined with subsequent high-precision signal conditioning, effectively resists the effects of external electromagnetic interference and power frequency noise.

[0022] Furthermore, this invention designs a highly stable bias voltage generation circuit, which solves the level mismatch problem between the dual-supply front-end and the single-supply A / D converter, precisely raising the reference terminal potential of the instrumentation amplifier to half the range of the A / D converter (e.g., 2.048V). This design retains the wide dynamic range advantage of the dual-supply amplifier circuit while ensuring that the bipolar differential signal is completely shifted to the effective acquisition range of the single-supply A / D converter (0~4.096V), avoiding negative voltage signal truncation and fully utilizing the resolution of the 24-bit ADC.

[0023] Furthermore, this invention incorporates a differential-mode plus common-mode hybrid input filter and a second-order active low-pass filter circuit along the signal path. These effectively filter out high-frequency noise and power frequency interference introduced by the motor drive, while retaining the effective low-frequency torque signal. Experimental verification shows that the repeatability error of this circuit is controlled at an extremely low level within a 50Nm range: 0.15% in the low-range segment and as low as 0.03%-0.04% in the mid-to-high-range segments, achieving the measurement goals of high precision and high stability. Attached Figure Description

[0024] Figure 1 This is the circuit schematic diagram of the present invention;

[0025] Figure 2 This is the overall circuit diagram of the present invention;

[0026] Figure 3 This is a circuit diagram of the high-precision reference voltage source module in this invention;

[0027] Figure 4 This is a circuit diagram of the charge pump module in this invention;

[0028] Figure 5 This is a circuit diagram of the signal amplification module in this invention;

[0029] Figure 6 This is the circuit diagram of the second-order filter module in this invention;

[0030] Figure 7 This is a circuit diagram of the A / D conversion module in this invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1 and Figure 2 As shown, the present invention is a high-precision signal conditioning and sampling circuit for strain gauge sensors, including a high-precision reference voltage source module, a charge pump module, a signal amplification module, a second-order filter module, and an A / D conversion module.

[0033] The high-precision reference voltage source module provides a highly stable 10V constant voltage excitation for the strain gauge sensor, ensuring that the sensor can generate millivolt-level differential voltage signals and guaranteeing signal purity from the source. The charge pump module converts the positive power supply to a negative power supply, creating a dual-power supply environment to ensure the linearity of subsequent analog signal processing circuits near zero. The signal amplification module amplifies the millivolt-level differential signal output by the strain gauge sensor. The second-order filter module receives the amplified differential signal and filters out high-frequency mechanical noise and electromagnetic interference, retaining the effective low-frequency analog voltage and torque signals. The A / D conversion module converts the filtered analog voltage signal into a high-precision digital signal for transmission to the microcontroller (MCU) for processing.

[0034] The following will provide a detailed explanation of the circuit structure, component connections, and functions of each module.

[0035] like Figure 3 As shown, the high-precision reference voltage source module uses the MAX6176 high-precision reference chip U2 as its core. Pin 2 of the high-precision reference chip U2 serves as the power input terminal, connected to the 12.6V positive power supply AVCC via input resistor R5. Capacitors C9 and C10 are connected in parallel between pin 2 and analog ground to filter out high-frequency and low-frequency noise from the input power supply. Pin 4 of the high-precision reference chip U2 is connected to analog ground, providing a common ground reference for the chip. Pin 6 of the high-precision reference chip U2 serves as the voltage output terminal, outputting a stable and accurate 10V voltage. To ensure the purity and stability of the voltage, pin 6 is first connected to filter capacitor C13 to analog ground, and then connected to VCC_10 via output resistor R8, serving as the power excitation input for the strain gauge sensor. In this embodiment, to reduce line impedance and voltage drop, resistors R5 and R8 are preferably 0Ω resistors, low-resistance resistors, or directly connected by wires.

[0036] The main parameters of the high-precision reference chip U2 are shown in Table 1. The MAX6176 was chosen because it has extremely high output accuracy of ±0.02%, extremely low noise (only 18uVp-p in the 0.1Hz~10Hz range), and extremely low temperature drift (3ppm / ℃). These parameters ensure the purity and stability of the signal source from the power supply side, which is the foundation for achieving high precision in the overall system.

[0037] The high-precision reference chip U2 has a maximum output current of 30mA. Taking a strain gauge sensor with an input impedance of 700Ω as an example, its operating current under 10V excitation is... The current requirements are fully met. In addition, compared with the traditional 3.3V or 5V power supply, this embodiment uses 10V high-voltage excitation, which increases the effective signal amplitude of the strain sensor output by 2-3 times, directly improving the signal-to-noise ratio from the signal source.

[0038]

[0039] Table 1

[0040] like Figure 4 As shown, the charge pump module uses the LTC3261 reverse charge pump chip U5 as its core. Pin 9 of the reverse charge pump chip U5 serves as the power input terminal, and pin 10 serves as the enable terminal. In this embodiment, to ensure that the reverse charge pump chip U5 is always operational, pins 9 and 10 are connected in parallel and then connected to the 12.6V positive power supply AVCC through an input resistor R4. Simultaneously, an input filter capacitor C7 is connected between pin 9 and analog ground to ensure the stability of the input power supply.

[0041] A flying capacitor C14 is connected between pins 5 and 8 of the reverse charge pump chip U5. Under the control of the chip's internal clock, capacitor C14 alternately charges and discharges, transferring the positive charge at the input terminal and reversing it to the output terminal, thereby realizing the voltage reversal function.

[0042] Pin 4 of the reverse charge pump chip U5 serves as the negative voltage output terminal. A capacitor C6 is connected between pin 4 and analog ground to smooth the output voltage ripple. The smoothed negative voltage is then output as a stable -12.6V negative power supply -AVCC through the output resistor R6 for use by subsequent signal amplification modules. Similarly, in this embodiment, the input resistor R4 and the output resistor R6 are preferably 0Ω resistors, low-resistance resistors, or directly connected by wires, mainly serving as jumper connections or current limiting protection.

[0043] In this embodiment, the reverse charge pump chip U5 is selected from LTC3261, mainly because it has high input voltage tolerance and low quiescent current characteristics, and can efficiently generate negative voltage output.

[0044] The charge pump module provides a -12.6V negative power supply to the signal amplification module and the second-order filter module. This means the signal amplification module can operate in a dual-supply environment of ±12.6V, significantly expanding the dynamic range of signal processing. In particular, the dual-supply system ensures good linearity even when the signal is close to 0V (zero point), completely eliminating the dead-zone problem of traditional single-supply circuits when acquiring weak signals, and ensuring that the amplification circuit maintains high accuracy while achieving high gain.

[0045] like Figure 5 As shown, the signal amplification module uses the AD8422D instrumentation amplifier U9 as its core. A hybrid filter circuit, comprising differential-mode filtering and common-mode filtering, is designed at the signal input terminal.

[0046] Two differential-mode filter capacitors, C40 and C41, are connected in parallel between the negative terminal SENSOR- and the positive terminal SENSOR+ of the differential signal of the strain gauge sensor. In this embodiment, the capacitance values ​​of C40 and C41 are both 22nF, and they are connected in parallel to form a differential-mode filter network with a total capacitance of 44nF, which is used to filter out differential-mode noise between the differential signal lines.

[0047] The negative terminal of the differential signal, SENSOR-, is connected to analog ground via capacitor C29, and the positive terminal of the differential signal, SENSOR+, is connected to analog ground via capacitor C43. Capacitors C29 and C43 together form a common-mode filter network to filter out common-mode interference and radio frequency noise from the signal line to ground.

[0048] This combination of dual differential-mode capacitors and dual common-mode capacitors can suppress complex electromagnetic interference in industrial environments to the greatest extent possible, ensuring that the instrumentation amplifier U9 receives a pure differential signal.

[0049] The filtered differential signals are connected to pins 1 and 4 of instrumentation amplifier U9, respectively. A gain resistor R30 is connected between pins 2 and 3. In this embodiment, the gain G of instrumentation amplifier U9 is calculated as follows:

[0050]

[0051] Where: 19.8kΩ is the internal feedback resistance constant of instrumentation amplifier U9; R is the resistance value of resistor R30.

[0052] In this embodiment, if the sensitivity of the strain gauge sensor is 1.0 mV / V, the gain factor needs to be set to approximately 200 times. Therefore, the gain resistor R30 is selected as a 100Ω high-precision low-temperature drift resistor with an accuracy of 0.01%. The actual gain is calculated as follows:

[0053]

[0054] The high-precision gain resistor R30 ensures the stability of the gain, resulting in a final signal gain accuracy of 0.04%.

[0055] Pin 8 of instrumentation amplifier U9 is connected to a +12.6V positive power supply, and pin 5 is connected to the voltage generated by the charge pump module. The negative power supply provides a dual power supply structure that ensures linearity when processing small signals.

[0056] To accommodate the subsequent single-supply A / D converter U10 (ADS1220), the bipolar differential signal needs to be shifted to a positive voltage range. A voltage follower is constructed using a dual-channel operational amplifier chip U8B, model TLE2062. Figure 2 and Figure 5As shown, the reference voltage source U1, model ADR4520, generates a 2.048V reference voltage. After being filtered by the filter capacitor C54, it is connected to the non-inverting input terminal (pin 5) of U8B. The inverting input terminal (pin 6) of U8B is shorted to the output terminal (pin 7), forming negative feedback. Pin 7 of U8B is connected to pin 6 of the instrumentation amplifier U9. In this way, U8B provides the instrumentation amplifier with a low-impedance, high-stability 2.048V DC bias voltage, accurately raising the zero-point potential of the amplified signal to 2.048V, thereby ensuring that the output signal is always within the effective acquisition range (0V~4.096V) of the A / D converter U10.

[0057] Pin 6 of instrumentation amplifier U9 is connected to a dual-channel operational amplifier chip U8B, model TLE2062, used to provide a highly stable bias voltage for the signal amplification module. Since the strain sensor outputs a bipolar differential signal (positive and negative voltage), and the A / D converter U10 (ADS1220) used in this embodiment is a single-supply device, it typically only acquires positive voltage signals. Therefore, by raising the reference ground potential to 2.048V, which is half of the A / D converter's range of 4.096V, the bipolar signal can be shifted into the linear acquisition range of the A / D converter (0~4.096V), thus preventing the negative voltage signal from being truncated. Specifically, as... Figure 2 and Figure 5 As shown, pin 5 of the dual-channel operational amplifier chip U8B is connected to a 2.048V reference voltage source U1. The reference voltage source U1 is an ADR4520. The 2.048V reference voltage generated is filtered by capacitor C54 and then connected to the non-inverting input of pin 5 of U8B. The inverting input of pin 6 of U8B is shorted to the output of pin 7, forming negative feedback. Pin 7 of U8B is connected to pin 6 of instrumentation amplifier U9. The dual-channel operational amplifier chip U8B acts as a voltage follower, introducing the 2.048V reference voltage U1 into instrumentation amplifier U9 and raising the zero point of the output signal of instrumentation amplifier U9 to 2.048V, thereby providing a low-impedance, high-stability DC bias voltage for the signal amplification module.

[0058] like Figure 6 As shown, the second-order filter module consists of an operational amplifier U8A (model TLE2062) and external first filter resistor R28, second filter resistor R29, first filter capacitor C30, and second filter capacitor C42, forming a second-order low-pass filter circuit. The specific connection relationship is as follows:

[0059] The differential signal from instrumentation amplifier U9 is connected in series with the first filter resistor R28 and the second filter resistor R29, and then connected to the non-inverting input of pin 3 of operational amplifier U8A. Pin 3 is grounded through the second filter capacitor C42.

[0060] The inverting input (pin 2) of operational amplifier U8A is directly shorted to the output (pin 1), forming a unity-gain voltage follower. One end of the first filter capacitor C30 is connected to the common node between the first filter resistor R28 and the second filter resistor R29, and the other end is connected to the common shorting line between pins 1 and 2 of operational amplifier U8A. This connection introduces positive feedback, thus forming a second-order low-pass filter circuit.

[0061] Transfer function of a second-order low-pass filter circuit Satisfy the following mathematical model:

[0062]

[0063] In a preferred embodiment of the present invention, the parameters are selected as follows: first filter resistor R28 = 20kΩ, second filter resistor R29 = 49.9kΩ, first filter capacitor C30 = 2.2μF, and second filter capacitor C42 = 1nF.

[0064]

[0065] in, For signal frequency, The value is an imaginary unit. This model shows that the circuit gain exhibits a second-order attenuation characteristic as the frequency increases.

[0066] The cutoff frequency of the second-order filter module is determined by the resistor and capacitor parameters in the circuit, as shown in the following formula:

[0067]

[0068] Based on the circuit theory model, the target cutoff frequency for this filter is approximately 100Hz to 110Hz. For example, in the theoretical calculations, the following parameters are selected: first filter resistor R28 = 20kΩ, second filter resistor R29 = 49.9kΩ, first filter capacitor C30 = 2.2μF, and second filter capacitor C42 = 1nF. The theoretical cutoff frequency, calculated using the formula, is approximately 107.4Hz.

[0069] However, in practical engineering applications, to match the standard resistance values ​​of components and consider the actual parasitic parameters of the circuit, this preferred embodiment has made engineering adjustments to the parameters: the first filter resistor R28 is selected as 24kΩ, and the second filter resistor R29 as 51kΩ. Substituting these preferred parameters into the formula for calculation:

[0070]

[0071] In the preferred embodiment, the 97Hz cutoff frequency is closer to the 100Hz interference frequency than the theoretical value of 107.4Hz. This fine-tuning allows the filter to have a greater attenuation at the 100Hz frequency point, thus achieving better anti-interference performance in practical applications. Therefore, the present invention can achieve the expected technical effect by setting the cutoff frequency within the range of 90Hz to 110Hz. The 97Hz cutoff frequency design can effectively filter out high-frequency noise and power frequency interference introduced by the motor drive, while retaining the effective low-frequency torque signal output by the strain gauge sensor, thereby significantly improving the signal-to-noise ratio and measurement accuracy of the system.

[0072] After the operational amplifier U8A outputs a signal from pin 1, the signal passes through a passive RC low-pass filter consisting of resistor R26 and capacitor C39 to further filter out high-frequency ripple. The final signal is then transmitted to the A / D conversion module U10 via output resistor R25. Similarly, resistor R25 is preferably a 0Ω resistor, a low-resistance resistor, or a wire, primarily serving to match impedance or facilitate connection adjustments. Furthermore, operational amplifier U8A uses the same ±12.6V dual power supply as the previous stage, with pin 8 connected to the positive power supply AVCC and pin 4 connected to the negative power supply -AVCC, ensuring consistent signal dynamic range.

[0073] like Figure 7 As shown, the A / D conversion module is used to acquire the torque signal after front-end conditioning and to monitor the system power supply voltage. The A / D conversion module is based on a 24-bit high-precision A / D converter U10, model ADS1220. The specific connection is as follows:

[0074] The output signal from the second-order filter module first passes through a differential filter network consisting of resistors R31 and R32 and capacitors C44 and C46. The output signal is connected to pin 6 of the A / D converter U10 via input resistor R31, serving as the positive input for differential sampling; analog ground is connected to pin 7 of U10 via resistors R34 and R32, serving as the negative input for differential sampling. Differential filter capacitor C46 is connected between pins 6 and 7 to filter out differential-mode noise. Common-mode filter capacitor C44 is connected between the signal input line Torque_OUT and ground.

[0075] To ensure the quantization accuracy of the analog-to-digital conversion, an external independent reference voltage source is configured for the A / D converter U10. The specific connection is as follows: a high-precision reference voltage of 4.096V, VCC_4.096, is connected to pin 9 of the A / D converter U10 as the positive input terminal of the reference voltage; pin 8 is connected to analog ground as the negative input terminal of the reference voltage.

[0076] Between pin 9 and pin 8, a large-value capacitor C55 and a small-value capacitor C49 are connected in parallel. Capacitor C55 is an energy storage capacitor, and capacitor C49 is a decoupling capacitor. This combination of high and low frequency capacitors can effectively filter out wideband noise on the reference voltage source and provide an extremely stable reference level for the A / D conversion module.

[0077] The power supply voltage monitoring signal BAT_VOL is connected to pin 11 of the A / D converter U10 as the positive input terminal for measurement. A capacitor C45 and a resistor R33 are connected in series on pin 11, with the other end of resistor R33 connected to pin 10 and analog ground. In this embodiment, resistor R33 is a 0Ω resistor. Through this connection, pin 10 of the A / D converter U10 is directly pulled low to the analog ground potential, serving as the negative reference terminal for single-ended measurement.

[0078] In the filter circuit, the high-precision reference voltage VCC_4.096V is connected to pin 9 of the A / D converter U10, and pin 8 is connected to analog ground. Capacitors C49 and C55 are connected in parallel between pins 9 and 8 to ensure the purity of the reference voltage.

[0079] In the decoupling circuit, pin 12 of the A / D converter U10 is connected to the 5V analog power supply AVCC_5, and capacitor C48 is connected between pin 12 and analog ground, forming an analog power supply decoupling circuit. Pin 13 of the A / D converter U10 is connected to the 3.3V digital power supply DVCC, and capacitor C47 is connected between pin 13 and digital ground, forming a digital power supply decoupling circuit. The A / D converter U10 communicates with the microcontroller MCU via the SPI interface.

[0080] In addition, the A / D conversion module is equipped with an auxiliary configuration circuit. The third pin of the analog-to-digital converter controller U10 is connected to digital ground, which constitutes a clock source configuration circuit to configure the chip in internal oscillator mode.

[0081] The A / D conversion module uses the ADS1220 chip because it is a high-precision, low-power 24-bit analog-to-digital converter (ADC) that supports multi-channel input and flexible configuration. It has a built-in high-precision reference voltage and PGA gain amplifier, enabling high signal-to-noise ratio and noise-free measurement. Its low-power design is suitable for battery-powered devices, and it also features strong anti-interference capabilities and good temperature stability.

[0082] To verify the beneficial effects of the technical solution of this invention, the above circuit was applied to a strain gauge torque sensor with a range of 50 Nm for actual measurement. The data are shown in Table 2:

[0083]

[0084] Table 2

[0085] Experimental data shows that at 0 Nm, the range of the AD values ​​measured three times is only 1.3. Ordinary single-supply op-amps often exhibit nonlinear dead zones or fail to output true 0 V when processing weak signals close to 0 V. This invention utilizes a charge pump to generate a -12.6V negative rail, ensuring that the signal remains within the op-amp's optimal linear region even at zero crossings, thus guaranteeing the high stability of only 1.3 range at 0 Nm as shown in the experimental data.

[0086] In the low range of 5Nm, the repeatability error is controlled at 0.15%; in the medium-high range of 20Nm-50Nm, the repeatability error is as low as 0.03%-0.04%.

[0087] This result fully demonstrates that the present invention has extremely high accuracy and stability when processing weak strain signals, and effectively solves the problems of poor anti-interference ability and low measurement accuracy in the prior art.

Claims

1. A high-precision signal conditioning and sampling circuit for strain gauge sensors, characterized in that: The high-precision reference voltage source module, the charge pump module, the signal amplification module, the second-order filter module and the A / D conversion module are included. The input end of the high-precision reference voltage source module is connected with a positive power supply, and the output end is connected to the power input end of the strain sensor, for providing constant voltage excitation for the strain sensor. The input end of the charge pump module is connected with the positive power supply, for converting the positive power supply into a negative power supply output, so as to build a dual power supply environment together with the positive power supply. The signal input end of the signal amplification module is connected with the differential signal output end of the strain sensor, and the power supply end of the signal amplification module is connected with the positive power supply and the negative power supply output by the charge pump module respectively, for amplifying the differential signal under the dual power supply environment. The second-order filter module is connected with the output end of the signal amplification module, for filtering noise signals. The A / D conversion module is connected with the output end of the second-order filter module, for converting analog signals into digital signals.

2. The high-precision signal conditioning sampling circuit applied to a strain sensor according to claim 1, characterized in that: The high-precision reference voltage source module includes a high-precision reference chip (U2), the power supply input end of the high-precision reference chip is connected with the system positive power supply through an input resistor (R5), and the output end outputs 10V constant voltage as the voltage output end as the constant voltage excitation; the voltage output end is connected to the strain sensor through an output resistor (R8), and the voltage output end is connected in parallel with a filter capacitor (C13) to the ground.

3. The high precision signal conditioning sampling circuit for strain gauge sensor according to claim 1, wherein, The charge pump module includes a reverse charge pump chip (U5) and a flying capacitor (C14), the input end of the reverse charge pump chip (U5) is connected with the system positive power supply, the flying capacitor (C14) is connected between the positive and negative connection ends of the flying capacitor of the reverse charge pump chip (U5); the negative voltage output by the output end of the reverse charge pump chip (U5) is equal in amplitude and opposite in polarity to the system positive power supply voltage, and the negative voltage is used as the negative power supply to provide negative rail power supply for the signal amplification module.

4. The high precision signal conditioning sampling circuit for strain gauge sensor according to claim 1, wherein, The signal amplification module includes an instrument amplifier (U9) and a bias voltage generation circuit; The instrument amplifier (U9) is powered by dual power supply, the positive power supply end is connected with the system positive power supply, and the negative power supply end is connected with the negative power supply generated by the charge pump module; The bias voltage generation circuit is used for generating a direct current bias voltage and is connected to the reference voltage input end of the instrument amplifier (U9), so as to lift the zero potential of the output signal of the instrument amplifier (U9) to the positive voltage interval.

5. The high precision signal conditioning sampling circuit applied to a strain gauge sensor according to claim 4, characterized in that, The bias voltage generation circuit includes a first reference voltage source (U1) and an operational amplifier (U8B); the first reference voltage source generates a first reference voltage, the voltage value of the first reference voltage is half of the reference voltage value of the A / D conversion module, and is connected to the non-inverting input end of the operational amplifier; the inverting input end of the operational amplifier is short-circuited with the output end to form a voltage follower; and the output end of the operational amplifier is connected to the reference voltage input end of the instrument amplifier (U9), so as to match the signal input range of the A / D conversion module.

6. The high precision signal conditioning sampling circuit for strain gauge sensor according to claim 4, wherein, The signal input end of the signal amplification module is further provided with a hybrid filter network; the hybrid filter network comprises a differential mode filter capacitor (C40, C41) connected in parallel between the positive and negative input ends of the differential signal, and a common mode filter capacitor (C29, C43) connected between the differential signal input end and the ground, respectively.

7. The high precision signal conditioning sampling circuit for strain gauge sensor according to claim 1, wherein, The second-order filter module comprises a second-order low-pass filter circuit composed of an operational amplifier (U8A); the operational amplifier (U8A) is powered by the same dual power supply as the signal amplification module; the cutoff frequency of the second-order low-pass filter circuit is configured to filter out power frequency interference and high-frequency noise.

8. The high precision signal conditioning sampling circuit for strain gauge sensor according to claim 1, wherein, The A / D conversion module comprises a 24-bit A / D converter (U10) and an external independent reference source; the external reference voltage input end of the A / D converter (U10) is connected with a second reference voltage generated by a second reference voltage source; the A / D converter (U10) has a positive input end and a negative input end for differential sampling; the common mode filter capacitor (C44) is connected between the signal input line of the positive input end and the ground; and the differential filter capacitor (C46) is connected in parallel between the positive input end and the negative input end.

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