Half-bridge strain gauge displacement sensor signal conditioning circuit and method

Abstract

The invention belongs to the related technical field of industrial displacement measurement, and discloses a half-bridge strain gauge displacement sensor signal conditioning circuit which comprises a half-bridge Wheatstone circuit module with manual zero setting, an RFI filtering module, a primary instrument operational amplifier module, a secondary precision amplifier module, an RC filtering module and a reverse following module which are sequentially connected in series. The half-bridge Wheatstone circuit module comprises a manual zero setting half-bridge Wheatstone circuit module and is used for dynamically compensating millivolt-level offset voltage caused by tolerance of a strain gauge and a fixed-value resistor; the RFI filtering module is used for suppressing rectification errors caused by radio frequency interference; the RC filtering module is used for suppressing high-frequency noise and smoothing a signal waveform; the reverse following module is used for realizing impedance isolation; two resistors are connected into a half-bridge Wheatstone circuit to form a manual zero setting module, millivolt-level offset voltage caused by tolerance of a strain gauge and a fixed-value resistor is dynamically compensated, and the problem that a traditional bridge sensor is insufficient in offset voltage and signal-to-noise ratio is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to industrial displacement measurement, and more specifically, relates to a signal conditioning circuit and method for a half-bridge strain gauge displacement sensor. Background Art

[0002] Bridge-type sensors are widely used in the field of industrial detection. Their core principle is to map the change of a physical quantity to be measured (such as stress, strain, torque, vibration frequency, etc.) or its derivative physical quantity (such as acceleration, angular displacement, etc.) into the change of the resistance of the bridge arm of the bridge circuit, and then quantitatively measure the physical quantity by detecting the resistance value. Due to their high sensitivity and linearity characteristics, such sensors are widely used in fields such as mechanical structure health monitoring, industrial automation control, and precision measurement systems. For example, in microstrain detection, a strain change of 1 με can cause a change in the bridge arm resistance of about 2 nΩ, and a measurement accuracy at the sub-microstrain level can be achieved by detecting the output voltage of the bridge. However, since the resistance change caused by the change of the conventional physical quantity is usually very weak, the effect of directly measuring the sensitive resistance is often not ideal. As the core implementation method of such sensors, the bridge uses sensitive resistors as the bridge arms. Through the bridge conversion technology, not only can the resistance value of the sensitive resistor be measured more accurately, but also the anti-interference ability and scaling performance of the sensor are significantly improved.

[0003] Bridge-type sensors face the following technical challenges in practical applications:

[0004] (1) Offset voltage problem caused by bridge arm resistance inconsistency: Due to the material characteristics of the strain gauge (such as the resistance temperature coefficient), the deviation of the bonding process, and the resistance tolerance (such as ±0.5%), the resistance value difference of each bridge arm resistance can cause an offset voltage in the millivolt range. Taking a typical half-bridge circuit (the bridge excitation voltage is 5V) as an example, when the bridge arm resistance ratio deviation ΔR / R = 0.2%, the offset voltage V os = 5 mV.

[0005] (2) Saturation risk in the amplification stage: The signal conditioning circuit usually needs to amplify microvolt-level signals by a hundred to a thousand times, and the output swing of a general operational amplifier (such as OPA2130) is limited to ±15V. The amplification of the millivolt-level offset voltage reduces the effective measurement range of the sensor and may even exceed the output range of the operational amplifier.

[0006] (3) Decrease in signal-to-noise ratio (SNR): The device noise in the circuit (such as resistor Johnson noise, operational amplifier input noise) is superimposed on the offset voltage and then amplified, resulting in a significant decrease in the system signal-to-noise ratio (SNR).

[0007] (4) Contradiction between cost and performance: To improve performance, high-precision resistors and ultra-low-noise operational amplifiers need to be used, but the BOM cost increases, which seriously restricts mass production. Summary of the Invention

[0008] In view of the above deficiencies or improvement requirements of the prior art, the present invention provides a signal conditioning circuit and method for a half-bridge strain gauge displacement sensor, aiming to dynamically compensate for the offset voltage and improve the signal-to-noise ratio, thereby solving the technical problem that the millivolt-level offset voltage is prone to cause the output saturation of the operational amplifier after amplification, resulting in a reduced effective measurement range.

[0009] To achieve the above object, according to one aspect of the present invention, there is provided a signal conditioning circuit for a half-bridge strain gauge displacement sensor, including a half-bridge Wheatstone circuit module with manual zero adjustment, an RFI filtering module, a first-stage instrumentation operational amplifier amplification module, a second-stage precision amplification module, an RC filtering module, and an inverting follower module connected in series in sequence;

[0010] The half-bridge Wheatstone circuit module with manual zero adjustment is used to dynamically compensate for the millivolt-level offset voltage caused by the tolerance of the strain gauge and the fixed resistor; its theoretical output voltage ±V o Satisfies the following relationship:

[0011]

[0012] Wherein, E is the excitation voltage, Δε is the strain of the strain gauge under unit displacement of the sensor, K is the sensitivity coefficient of the strain gauge; ±ΔS is the bilateral range of the displacement sensor;

[0013] The RFI filtering module is used to suppress the rectification error caused by radio frequency interference;

[0014] The first-stage instrumentation operational amplifier amplification module is used to preliminarily amplify the microvolt-level differential signal filtered by the RFI filtering module and suppress the common-mode interference;

[0015] The second-stage precision amplification module is used to further amplify the voltage signal output by the first-stage instrumentation operational amplifier amplification module;

[0016] The RC filtering module is used to filter out the high-frequency noise interference mixed in the voltage signal output by the second-stage precision amplification module and smooth the signal waveform;

[0017] The inverting follower module is used to achieve impedance isolation and isolate and output the voltage signal processed by the RC filtering module.

[0018] Preferably, the half-bridge Wheatstone circuit module with manual zero adjustment includes fixed resistors R1, R2, strain gauge resistors R3, R4, a zero-adjustment resistor R5, and a sliding rheostat R6; the fixed resistors R1, R2 and the strain gauge resistors R3, R4 are connected in the form of a Wheatstone half-bridge, the sliding rheostat R6 is connected in parallel across the excitation voltage, and the fixed resistor R5 is connected in series between the sliding port of the sliding rheostat R6 and the connection port of the strain gauges R3, R4.

[0019] Preferably, the RFI filtering module includes a differential-mode filter and a common-mode filter. The differential-mode filter includes fixed-value resistors R 7a , R 7b , and capacitor C2; one end of the fixed-value resistor R 7a is connected in series to output port 1 of the half-bridge Wheatstone circuit module with a manual zero-adjustment function, the other end of the fixed-value resistor R 7a is connected in series to one end of capacitor C2, the other end of capacitor C2 is connected in series to one end of the fixed-value resistor R 7b , and the other end of the fixed-value resistor R 7b is connected in series to output port 2 of the half-bridge Wheatstone circuit module with a manual zero-adjustment function; the common-mode filter includes capacitors C 1a , C 1b , one ends of the capacitors C 1a , C 1b are respectively connected to the ground plane of the conditioning board, and the other ends are respectively connected to both ends of capacitor C2.

[0020] Preferably, the fixed-value resistors B 7a , R 7b are 1% precision metal film resistors.

[0021] Preferably, the tolerance of the capacitors C 1a , C 1b is controlled within ±5%.

[0022] According to another aspect of the present invention, a method for conditioning the signal of a half-bridge strain gauge displacement sensor is provided, including the following steps:

[0023] S1: According to the technical specifications of the subsequent measurement system, calculate the sensor sensitivity S and the total amplification factor A of the signal conditioning circuit total ;

[0024] S2: Based on the total amplification factor A of the signal conditioning circuit total , combined with the common-mode voltage range, output voltage amplitude, noise characteristics, output voltage range of the half-bridge Wheatstone circuit module with a manual zero-adjustment function, as well as the bandwidth, offset voltage, and noise characteristics of the cascaded precision operational amplifier, determine the strain gauge model parameters, bridge arm fixed-value resistor parameters, output differential signal bandwidth of the half-bridge Wheatstone circuit module with a manual zero-adjustment function, and the input noise level, amplification factor of the first-stage instrumentation amplifier module, amplification factor of the second-stage precision amplification module, and control cycle parameters of the sensor system;

[0025] S3: Based on the strain gauge model parameters and the fixed-value resistor parameters of the bridge arm obtained in S2, preliminarily set the resistance values of the zero-adjustment resistor R5 and the sliding rheostat R6 in the half-bridge Wheatstone circuit module with manual zero adjustment. Calculate the zero-adjustment range through the Y-Δ resistor equivalent transformation formula. If the resistance values of R5 and R6 meet the calculated zero-adjustment range, the setting of the half-bridge Wheatstone circuit module with manual zero adjustment has the ability to compensate for the offset voltage; if R the resistance values of R5 and R6 do not meet the calculated zero-adjustment range, reset the resistance values of R5 and R6 until they meet the calculated zero-adjustment range;

[0026] Based on the input noise level parameters of the first-stage instrumentation amplifier module obtained in S2 and the output differential signal bandwidth of the half-bridge Wheatstone circuit module with manual zero adjustment, calculate the -3dB differential mode bandwidth and common mode bandwidth of the RFI filter module, and determine the fixed-value resistor and capacitor parameters in the RFI filter module;

[0027] Set the time constant of the RC filter module based on the control cycle parameters of the sensor system obtained in S2, and calculate the fixed-value resistor R12 and capacitor C3 parameters in the RC filter module;

[0028] S4: After solidifying the signal conditioning circuit setting parameters calculated based on the above steps, conduct a composite re-inspection of the designed measurement system based on the measurement value output by the sensor signal conditioning circuit.

[0029] Preferably, in step S1, the sensor sensitivity S and the total amplification factor A total of the signal conditioning circuit are calculated by the following formulas respectively:

[0030]

[0031] where, ±ΔS is the bilateral range of the displacement sensor, given by the technical indicators of the measurement system; ±V adc is the bilateral range of the input voltage of the ADC of the measurement system; ±V o is the theoretical output voltage of the half-bridge Wheatstone circuit module with manual zero adjustment function within the working range of the displacement sensor.

[0032] Preferably, in step S3, the calculation formula for the equivalent bridge arm resistance obtained by the Y-Δ resistor equivalent transformation formula is as follows:

[0033] R3’ = R3 / / R 56L

[0034] R4’ = R4 / / R 56R

[0035]

[0036] Among them, R3 and R4 are the actual resistances of strain gauge 1 and strain gauge 2 respectively, R5 is the zero-adjusting resistance, and R6 is the resistance value of the sliding rheostat; R 6L , R 6R are the resistance values of the left and right resistance wires of the sliding rheostat during the sliding process respectively;

[0037] When the following inequality formula is satisfied, the resistance values of R5 and R6 meet the zero-adjusting range after calculation. The inequality formula is:

[0038]

[0039] Among them, R1 and R2 are the first fixed resistance and the second fixed resistance in the half-bridge Wheatstone circuit module with manual zero adjustment respectively.

[0040] Preferably, in step S3, the fixed resistance R in the RFI filter module 7a , R 7b The calculation formula is as follows:

[0041] R 7a = R 7b = R7

[0042]

[0043] Among them, e is the thermal noise of the fixed resistance R 7a , R 7b , K0 is the Boltzmann constant, T is the absolute temperature of the fixed resistance R 7a , R 7b , and e1 is the input noise level parameter of the first-stage instrumentation amplifier module.

[0044] Preferably, in step S3, the time constant τ of the RC filter module and the fixed resistance R in the RC filter module 12 , capacitor C3 calculation formula is as follows:

[0045] τ ≤ 0.1T

[0046] R 12 = 10R out

[0047] C3 = τ / R 12

[0048] Among them, T is the control period of the measurement system, and R out is the output resistance of the second-stage precision amplification module.

[0049] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, a semi-bridge strain gauge displacement sensor signal conditioning circuit and method provided by the present invention mainly have the following beneficial effects:

[0050] 1. The present invention forms a manual zero - adjustment module by connecting two resistors in a half - bridge Wheatstone circuit, dynamically compensating for the millivolt - level offset voltage caused by the tolerance of strain gauges and fixed - value resistors. Compared with before compensation, the effective measurement range of the sensor is significantly increased.

[0051] 2. The present invention adopts a cascaded operational - amplifier connection scheme, and the circuit adds RFI filtering and RC filtering to improve the signal - to - noise ratio of the sensor.

[0052] 3. The signal conditioning method proposed by the present invention has a wide range of applications, and is applicable not only to half - bridge Wheatstone bridges, but also to 1 / 4 - bridge and full - bridge Wheatstone bridges.

[0053] 4. The present invention can control costs to the maximum extent on the premise of ensuring the performance of the sensor, which is conducive to mass production. Description of the Drawings

[0054] Figure 1 is a schematic diagram of a traditional half - bridge strain - gauge circuit;

[0055] Figure 2 is a schematic diagram of a half - bridge Wheatstone circuit module with manual zero - adjustment according to the present invention;

[0056] Figure 3 is an equivalent - circuit schematic diagram of a half - bridge Wheatstone circuit module with manual zero - adjustment according to the present invention;

[0057] Figure 4 is a schematic diagram of a signal conditioning circuit for a half - bridge strain - gauge displacement sensor according to the present invention. Detailed Embodiments

[0058] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0059] Taking the following technical indicators of a displacement - sensor system as an example in this embodiment, the displacement measurement range is ±ΔS = ±300μm; the strain - gauge model is the KFGS - 3 - 350 - C1 - 11 strain gauge produced by KYOWA Company, with a sensitivity coefficient K = 2.13, a resistance value range of 350Ω ± 0.2%, and the resistance value ranges of the selected resistors R1 and R2 are 350Ω ± 0.01%; the supply voltage of the strain - gauge half - bridge circuit is E = 5V; when the displacement sensor detects a unit displacement, the strain of the strain gauge is Δε = 1.002μ; the subsequent ADC sampling voltage range is ΔV abc= 10V. Design a corresponding signal conditioning circuit for the half-bridge strain gauge displacement sensor according to the technical specifications of the displacement sensor system. Please refer to Figure 4 , including a half-bridge Wheatstone circuit module with manual zero adjustment, an RFI filtering module, a first-stage instrumentation amplifier module, a second-stage precision amplifier module, an RC filtering module, and an inverting follower module connected in series in sequence;

[0060] The half-bridge Wheatstone circuit module with manual zero adjustment is used to dynamically compensate for the millivolt-level offset voltage caused by the tolerance of the strain gauge and the fixed resistor; its theoretical output voltage ±V o Satisfies the following relationship:

[0061]

[0062] Among them, E is the excitation voltage, Δε is the strain of the strain gauge under unit displacement of the sensor, K is the sensitivity coefficient of the strain gauge; ±ΔS is the bilateral range of the displacement sensor;

[0063] The RFI filtering module is used to suppress the rectification error caused by radio frequency interference;

[0064] The first-stage instrumentation amplifier module is used to initially amplify the microvolt-level differential signal filtered by the RFI filtering module and suppress the common-mode interference;

[0065] The second-stage precision amplifier module is used to further amplify the voltage signal output by the first-stage instrumentation amplifier module;

[0066] The RC filtering module is used to filter out the high-frequency noise interference mixed in the voltage signal output by the second-stage precision amplifier module and smooth the signal waveform;

[0067] The inverting follower module is used to achieve impedance isolation and isolate and output the voltage signal processed by the RC filtering module.

[0068] The half-bridge Wheatstone circuit module with manual zero adjustment includes fixed resistors R1, R2, strain gauge resistors R3, R4, a zero-adjustment resistor R5, and a sliding rheostat R6; the fixed resistors R1, R2 and the strain gauge resistors R3, R4 are connected in the form of a Wheatstone half-bridge, the sliding rheostat R6 is connected in parallel across the excitation voltage, and the fixed resistor R5 is connected in series between the sliding port of the sliding rheostat R6 and the connection port of the strain gauges R3, R4.

[0069] The RFI filtering module includes a differential-mode filter and a common-mode filter. The differential-mode filter includes fixed resistors R 7a , R 7b , and capacitor C2; one end of the fixed resistor R 7a is connected in series to the output port 1 of the half-bridge Wheatstone circuit module with manual zero adjustment function, and one end of the fixed resistor R 7aThe other end of which is connected in series with one end of capacitor C2, and the other end of capacitor C2 is connected in series with a fixed-value resistor R 7b at one end, and the fixed-value resistor R 7b at the other end is connected in series with output port two of a half-bridge Wheatstone circuit module with a manual zero-adjustment function; The common-mode filter includes capacitor C 1a 、C 1b , capacitor C 1a 、C 1b at one end are respectively connected to the ground plane of the conditioning board, and the other ends are respectively connected to both ends of capacitor C2.

[0070] The fixed-value resistor R 7a 、R 7b selects metal film resistors with 1% accuracy. Capacitor C 1a 、C 1b has a tolerance controlled within ±5%, which can improve the common-mode noise suppression performance of the RFI filter module. Capacitor C 1a , C 1b , C2 is set as a ±5% silver-plated mica capacitor, a small mica capacitor or a new Panasonic ±2% polyphenylene sulfide (PPS) thin film capacitor.

[0071] Please refer to Figure 1 , which is a schematic diagram of a traditional half-bridge strain gauge circuit, and its maximum offset voltage is:

[0072]

[0073] This offset voltage will exceed the output limit of a general operational amplifier after being amplified by the conditioning circuit.

[0074] This embodiment provides a method for a signal conditioning circuit of a half-bridge strain gauge displacement sensor, including the following steps:

[0075] S1: According to the technical specifications of the subsequent measurement system, calculate the sensor sensitivity S and the total amplification factor A of the signal conditioning circuit total ;

[0076]

[0077] Among them, ±ΔS is the bilateral range of the displacement sensor, which is given by the technical specifications of the measurement system; ±V adc is the bilateral range of the input voltage of the ADC of the measurement system; ±V o is the theoretical output voltage of the half-bridge Wheatstone circuit module with a manual zero-adjustment function within the working range of the displacement sensor; The coefficient is set to 0.8 to prevent the analog signal output from the conditioning circuit to the ADC from overflowing.

[0078] S2: Based on the total amplification factor A of the signal conditioning circuit total, determine the strain gauge model parameters, fixed resistance parameters of the bridge arm of the bridge, output differential signal bandwidth of the half-bridge Wheatstone circuit module with manual zero adjustment function, input noise level of the first-stage instrumentation amplifier module, amplification factor, amplification factor of the second-stage precision amplification module, and control cycle parameters of the sensor system by combining the common-mode voltage range, output voltage amplitude, noise characteristics, output voltage range of the half-bridge Wheatstone circuit module with manual zero adjustment function, and the bandwidth, offset voltage and noise characteristics of the cascaded precision operational amplifier;

[0079] Among them, the common-mode voltage of the half-bridge Wheatstone circuit module with manual zero adjustment function The first-stage instrumentation amplifier module selects AD620, and the amplification factor A1 is 200 times; the feedback resistor R8 is 248 Ω;

[0080] The second-stage precision amplification module selects OPA2130, adopts a negative feedback amplification connection method, the amplification factor A2 is 25 times (set A1 to be much larger than A2 to improve the signal-to-noise ratio of the conditioning circuit), the resistor R9 is 4 kΩ, and according to the relationship between the negative feedback amplification factor and the feedback resistor Resistor R 10 is 100 kΩ; in order to reduce the voltage offset caused by current offset at the output end of U2, a resistor R is connected in parallel at the non-inverting input end of U2 11 , Take the standard value of 3.9 kΩ;

[0081] S3: Based on the strain gauge model parameters and fixed resistance parameters of the bridge arm of the bridge obtained in S2, initially set the resistance values of the zero-adjustment resistor R5 and the sliding rheostat R6 in the half-bridge Wheatstone circuit module with manual zero adjustment, and calculate the zero-adjustment range through the Y-Δ resistor equivalent transformation formula. If the resistance values of R5 and R6 meet the calculated zero-adjustment range, the setting of the half-bridge Wheatstone circuit module with manual zero adjustment has the ability to compensate for the offset voltage; if the resistance values of R5 and R6 do not meet the calculated zero-adjustment range, reset the resistance values of R5 and R6 until they meet the calculated zero-adjustment range;

[0082] Among them, the calculation formula for the equivalent bridge arm resistance obtained from the Y-Δ resistor equivalent transformation formula is as follows:

[0083] R3’ = R3 / / R 56L

[0084] R4’ = R4 / / R 56R

[0085]

[0086] Among them, R3 and R4 are the actual resistances of strain gauge 1 and strain gauge 2 respectively, R5 is the zero-adjustment resistor, and R6 is the resistance value of the sliding rheostat; R 6L , R6R They are the resistance values of the left and right resistance wires during the sliding process of the rheostat, respectively.

[0087] When the following inequality formula is satisfied, the resistance values of R5 and R6 meet the adjusted zero range after calculation. The inequality formula is:

[0088]

[0089] Among them, R1 and R2 are the first fixed resistor and the second fixed resistor in the half-bridge Wheatstone circuit module with manual zero adjustment, respectively.

[0090] In this embodiment, reference can be made to Figure 2 , which is a schematic diagram of the half-bridge Wheatstone circuit module with manual zero adjustment. The manual conditioning function is realized by introducing resistors R5 and R6 into the traditional half-bridge strain gauge circuit to eliminate the offset voltage. Among them, R 1、 The resistance value range of R2 is 350Ω ± 0.01%, the value of R5 is 18kΩ, and the value of R6 is 10kΩ. After calculation, Therefore, the selection of the resistance values of R5 and R6 can eliminate the zero drift caused by the resistance tolerance of the strain gauge and the fixed resistor. The setting of this half-bridge Wheatstone circuit module with manual zero adjustment has the ability to compensate for the offset voltage.

[0091] Based on the input noise level parameter of the first-stage instrumentation amplifier module obtained from S2, and the output differential signal bandwidth of the half-bridge Wheatstone circuit module with manual zero adjustment, calculate the -3dB differential mode bandwidth and common mode bandwidth of the RFI filter module, and determine the fixed resistor and capacitor parameters in the RFI filter module;

[0092] The fixed resistor R in the RFI filter module 7a , R 7b The calculation formula is as follows:

[0093] R 7a =R 7b =R7

[0094]

[0095] Among them, e is the thermal noise of the fixed resistor R 7a , R 7b . K0 is the Boltzmann constant, T is the absolute temperature of the fixed resistor R 7a , R 7b . e1 is the input noise level parameter of the first-stage instrumentation amplifier module. The calculation formula for the -3dB differential mode bandwidth of the RFI filter link is as follows:

[0096]

[0097] Among them, BW is the differential voltage signal bandwidth output by the half-bridge Wheatstone circuit module with manual zero adjustment function, and C1 = C 1a = C1, C1 < 0.1C2.

[0098] The -3dB common-mode bandwidth calculation formula of the RFI filter section is as follows:

[0099]

[0100] The average input noise spectral density of the AD620 selected in this embodiment is According to R7a and R7b in series, the Johnson noise spectral density is lower than the input noise spectral density of the previous-stage operational amplifier, that is Substitute K = 1.38 * 10 -23 J / K, T = 298K, calculate R7 < 9.8kΩ, take the standard value, R 7a = R 7b = 4.02kΩ. According to the RFI filter -3dB differential bandwidth being 10 times the differential bandwidth of the highest signal frequency, BW DIFF = 400Hz, Select the standard value C2 = 47nF, C 1a = C 1b = C1 < 0.1C2 = 4.7nF, select the standard value C1 = 1nF.

[0101] Based on the control period parameter of the sensor system obtained from S2, set the time constant of the RC filter module, and calculate the fixed-value resistor R 12 and capacitor C3 parameters in the RC filter module;

[0102] The time constant τ of the RC filter module and the fixed-value resistor R 12 and capacitor C3 in the RC filter module are calculated as follows:

[0103] τ ≤ 0.1T

[0104] R 12 = 10R out

[0105] C3 = τ / R 12

[0106] Among them, T is the control period of the measurement system, and R out is the output resistance of the secondary precision amplification module.

[0107] In this embodiment, the control period T of the sensor system is 1ms, initially select R 12 equal to 20kΩ, obtain C3 ≤ 5nF, take the standard value, C3 = 5nF.

[0108] S4: After solidifying the signal conditioning circuit setting parameters calculated based on the above steps, perform a composite re-verification of the displacement measurement accuracy and offset voltage compensation ability of the designed measurement system based on the measurement values output by the sensor signal conditioning circuit.

[0109] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A signal conditioning circuit for a half-bridge strain gauge displacement sensor, characterized in that: It includes a half-bridge Wheatstone circuit module with manual zero adjustment, an RFI filtering module, a first-stage instrumentation operational amplifier amplification module, a second-stage precision amplification module, an RC filtering module, and an inverting follower module, which are connected in series in sequence; The half-bridge Wheatstone circuit module with manual zero adjustment is used to dynamically compensate for the millivolt-level offset voltage caused by the tolerance of the strain gauge and the fixed resistor; its theoretical output voltage is ±V o Satisfies the following relationship: where E is the excitation voltage, Δε is the strain of the strain gauge under unit displacement of the sensor, K is the sensitivity coefficient of the strain gauge; ±ΔS is the bilateral range of the displacement sensor; The RFI filtering module is used to suppress the rectification error caused by radio frequency interference; The first-stage instrumentation operational amplifier amplification module is used to preliminarily amplify the microvolt-level differential signal filtered by the RFI filtering module and suppress the common-mode interference; The second-stage precision amplification module is used to further amplify the voltage signal output by the first-stage instrumentation operational amplifier amplification module; The RC filtering module is used to filter out the high-frequency noise interference mixed in the voltage signal output by the second-stage precision amplification module and smooth the signal waveform; The inverting follower module is used to achieve impedance isolation and isolate and output the voltage signal processed by the RC filtering module.

2. The signal conditioning circuit of a half-bridge strain gauge displacement sensor according to claim 1, wherein: The half-bridge Wheatstone circuit module with manual zero adjustment includes fixed resistors R1, R2, strain gauge resistors R3, R4, zero adjustment resistor R5, and sliding rheostat R6; the fixed resistors R1, R2 and the strain gauge resistors R3, R4 are connected in the form of a Wheatstone half-bridge, the sliding rheostat R6 is connected in parallel across the excitation voltage, and the fixed resistor R5 is connected in series between the sliding port of the sliding rheostat R6 and the connection port of the strain gauges R3, R4.

3. The signal conditioning circuit of a half-bridge strain gauge displacement sensor according to claim 1, wherein: The RFI filtering module includes a differential-mode filter and a common-mode filter. The differential-mode filter includes fixed-value resistors R 7a , R 7b , and capacitor C2. One end of the fixed-value resistor R 7a is connected in series with output port 1 of the half-bridge Wheatstone circuit module with a manual zero-adjustment function. The other end of the fixed-value resistor R 7a is connected in series with one end of capacitor C2. The other end of capacitor C2 is connected in series with one end of the fixed-value resistor R 7b . The other end of the fixed-value resistor R 7b is connected in series with output port 2 of the half-bridge Wheatstone circuit module with a manual zero-adjustment function. The common-mode filter includes capacitors C 1a , C 1b . One end of the capacitors C 1a , C 1b is respectively connected to the ground plane of the conditioning board, and the other end is respectively connected to both ends of capacitor C2.

4. The signal conditioning circuit of a half-bridge strain gauge displacement sensor according to claim 3, characterized in that: The fixed-value resistor R 7a , R 7b Select metal film resistors with 1% accuracy.

5. The signal conditioning circuit of a half-bridge strain gauge displacement sensor according to claim 3, characterized in that: The capacitor C 1a , C 1b has a tolerance controlled within ±5%.

6. The method of the signal conditioning circuit of the half-bridge strain gauge displacement sensor according to any one of claims 1-5, characterized in that: It includes the following steps: S1: Calculate the sensor sensitivity S and the total amplification factor A of the signal conditioning circuit according to the technical specifications of the subsequent measurement system total ; S2: Based on the total amplification factor A of the signal conditioning circuit total , combined with the common-mode voltage range, output voltage amplitude, noise characteristics, output voltage range of the half-bridge Wheatstone circuit module with manual zero adjustment function, as well as the bandwidth, offset voltage and noise characteristics of the cascaded precision operational amplifier, determine the strain gauge model parameters, fixed-value resistance parameters of the bridge arm of the bridge, output differential signal bandwidth of the half-bridge Wheatstone circuit module with manual zero adjustment function, input noise level of the first-stage instrumentation amplifier module, amplification factor, amplification factor of the second-stage precision amplification module, and control cycle parameters of the sensor system; S3: Based on the strain gauge model parameters and the fixed resistor parameters of the bridge arm of the Wheatstone bridge obtained in S2, preliminarily set the resistance values of the zero adjustment resistor R5 and the sliding rheostat R6 in the half-bridge Wheatstone circuit module with manual zero adjustment, calculate the zero adjustment range through the Y-Δ resistance equivalent transformation formula. If the resistance values of R5 and R6 meet the calculated zero adjustment range, the setting of the half-bridge Wheatstone circuit module with manual zero adjustment has the ability to compensate for the offset voltage; if the resistance values of R5 and R6 do not meet the calculated zero adjustment range, reset the resistance values of R5 and R6 until they meet the calculated zero adjustment range; Based on the input noise level parameters of the first-stage instrumentation operational amplifier amplification module obtained in S2 and the output differential signal bandwidth of the half-bridge Wheatstone circuit module with manual zero adjustment, calculate the -3dB differential mode bandwidth and common mode bandwidth of the RFI filtering module, and determine the fixed resistor and capacitor parameters in the RFI filtering module; Set the time constant of the RC filter module based on the control cycle parameter of the sensor system obtained from S2, and calculate the fixed resistor R and the capacitance C3 parameter in the RC filter module; 12 and capacitance C3 parameter; S4: After solidifying the signal conditioning circuit setting parameters calculated based on the above steps, conduct a composite re-inspection on the designed measurement system based on the measured value output by the sensor signal conditioning circuit.

7. A signal conditioning method for a half-bridge strain gauge displacement sensor according to claim 6, characterized in that: In step S1, the sensor sensitivity S and the total amplification factor A of the signal conditioning circuit total are calculated by the following formulas respectively: where, ±ΔS is the bilateral range of the displacement sensor, which is given by the technical specifications of the measurement system; ±V adc is the bilateral range of the input voltage of the ADC of the measurement system; ±V o is the theoretical output voltage of the half-bridge Wheatstone circuit module with a manual zero adjustment function within the operating range of the displacement sensor.

8. A signal conditioning method for a half-bridge strain gauge displacement sensor according to claim 6, characterized in that: In step S3, the time constant τ of the RC filtering module, the fixed-value resistor in the RC filtering module, and the capacitor R 12 , and the calculation formula of C3 is as follows: τ ≤ 0.1T R 12 = 10R out C 13 = τ / R 12 where T is the control period of the measurement system, and R out is the output resistance of the second-stage precision amplification module.

9. A signal conditioning method for a half-bridge strain gauge displacement sensor according to claim 6, characterized in that: In step S3, the calculation formula for the equivalent bridge arm resistance obtained from the Y-Δ resistance equivalent transformation formula is as follows: R3' = R3 / / R 56L R4' = R4 / / R 56R Among them, R3 and R4 are the actual resistances of strain gauge 1 and strain gauge 2 respectively, R5 is the zero-adjusting resistance, and R6 is the resistance value of the sliding rheostat; R 6L , R 6R are the resistance values of the left and right resistance wires of the sliding rheostat during the sliding process respectively; When the following inequality formula is satisfied, the resistance values of R5 and R6 meet the calculated zero adjustment range, and the inequality formula is: where R1 and R2 are the first fixed resistor and the second fixed resistor in the half-bridge Wheatstone circuit module with manual zero adjustment respectively.

10. A signal conditioning method for a half-bridge strain gauge displacement sensor according to claim 6, characterized in that: In step S3, the fixed resistor R in the RFI filter module 7a , R 7b The calculation formula is as follows: R 7a = R 7b = R7 where e is the fixed resistor R 7a , R 7b 's thermal noise, K0 is the Boltzmann constant, and T is the absolute temperature of the fixed resistor R 7a , R 7b , and e1 is the input noise level parameter of the first-stage instrumentation amplifier module.

Images