Isolation circuit, parameter design system and design method for bridge sensor

Abstract

The present invention discloses an isolation circuit, parameter design system, and design method for bridge sensors, belonging to the field of sensor signal conditioning and isolation. The isolation circuit for a bridge sensor comprises a power supply portion and a signal portion, wherein the power supply portion includes a power supply, a protection circuit, a first RC filter circuit, a DC-DC isolation power supply, a voltage reference circuit, and an excitation source connected in series. The signal portion includes a signal input terminal, a magnetic bead filter circuit, a second RC filter circuit, an isolation amplifier, a voltage divider resistor network, an operational amplifier circuit, a third RC filter circuit, and a signal output terminal connected in series. By employing the isolation circuit, parameter design system, and design method for a bridge sensor, high-precision, anti-interference, isolated, and proportional transmission of bridge sensor signals is achieved through precise selection of isolation amplifiers, rational configuration of voltage dividers and filter circuits, and combined with anti-interference parameter analysis. This balances signal conditioning and noise suppression, ensuring system stability and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor signal conditioning and isolation, and in particular to an isolation circuit, a parameter design system and a design method for a bridge sensor. Background Art

[0002] Bridge sensors are widely used in the industrial field. They use a Wheatstone bridge circuit composed of four resistors to convert resistance changes caused by mechanical force, pressure or temperature into voltage changes, thereby accurately measuring physical quantities such as strain, pressure and temperature. Therefore, they are often used in industrial control, laboratory liquid or gas pressure measurement and other occasions.

[0003] However, bridge sensors transmit very small differential signals and are therefore susceptible to electromagnetic interference and noise. To mitigate interference issues in industrial applications, shielded cables, isolation, and filtering are often employed. A good ground connection is also maintained between the sensor and the measurement device to ensure accurate signal transmission and measurement.

[0004] Existing technologies have many limitations in bridge sensor signal processing, making it difficult to meet the requirements for stable signal transmission and accurate measurement in industrial environments with strong interference. Specifically,

[0005] 1. Power supply: Using a non-isolated linear regulated power supply or simple DC-DC conversion, there is no electrical isolation between the power supply and signal circuits, causing grid noise and load fluctuations to be directly transmitted to the sensor excitation source, causing the reference voltage to drift.

[0006] 2. Signal voltage division conditioning: Using a single resistor voltage divider circuit to adjust the signal amplitude is greatly affected by the resistor tolerance and temperature coefficient. The voltage division error exceeds 1%, which cannot meet the high-precision measurement requirements of ±0.1%, and cannot offset the nonlinear signal distortion caused by ambient temperature changes.

[0007] 3. Isolation and anti-interference: When ordinary differential amplifiers are used instead of dedicated isolation amplifiers, or simple isolation is achieved through optocouplers, the common-mode rejection ratio (CMRR) is generally less than 80dB, making it difficult to suppress the hundreds of volts of common-mode voltage commonly found in industrial environments. Filter designs often use a single RC network, which cannot cover the wide-band high-frequency noise of 10kHz to 1MHz, and the signal-to-noise ratio (SNR) is less than 60dB.

[0008] 4. System adaptability: The hardware conditioning accuracy is insufficient, and the signal needs to be recalibrated by software. This increases the system complexity and introduces real-time delays, making it unsuitable for dynamic measurement scenarios. Fixed output amplitude (such as a single 0-5V) is difficult to adapt to different post-stage acquisition devices and has poor compatibility. Summary of the Invention

[0009] The purpose of the present invention is to provide an isolation circuit, a parameter design system and a design method for a bridge sensor to solve the above technical problems.

[0010] To achieve the above-mentioned object, the present invention provides an isolation circuit for a bridge sensor, comprising a power supply portion and a signal portion, wherein the power supply portion comprises a power supply, a protection circuit, a first RC filter circuit, a DC-DC isolation power supply, a voltage reference circuit, and an excitation source connected in series in sequence;

[0011] The signal part includes a signal input terminal, a magnetic bead filter circuit, a second RC filter circuit, an isolation amplifier, a voltage divider resistor network, an operational amplifier circuit, a third RC filter circuit and a signal output terminal connected in series in sequence;

[0012] The DC-DC isolated power supply is used to convert the voltage input by the power supply into two isolated outputs. One output is used to power the voltage reference circuit, and the other output is used to power the isolation amplifier after being stepped down by a low-dropout linear regulator.

[0013] Preferably, the voltage divider resistor network is composed of an upper bridge arm and a lower bridge arm, which is used to divide the amplified signal according to the voltage divider ratio. reduction;

[0014] The voltage reference circuit includes a controllable precision voltage-stabilizing source, wherein the K electrode of the controllable precision voltage-stabilizing source is respectively connected to one end of a first resistor and the base of a transistor, the other end of the first resistor and the collector of the transistor are both connected to the output end of a DC-DC isolated power supply, the emitter of the transistor is respectively connected to one end of a second resistor and an excitation source, the other end of the second resistor is connected in series with a third resistor and then grounded, the second resistor and the third resistor are connected to the R electrode of the controllable precision voltage-stabilizing source via a lead, and the A electrode of the controllable precision voltage-stabilizing source is grounded;

[0015] And the output voltage of the voltage reference circuit and the excitation source voltage of the original bridge sensor The following proportional relationship is satisfied:

[0016] (1) Among them,

[0017] (2);

[0018] Where, Indicates the amplification factor of the isolation amplifier, and Represent the resistance values ​​of the first resistor and the second resistor respectively, Indicates the reference voltage of the controllable precision voltage regulator.

[0019] Preferably, the voltage divider resistor network includes an upper bridge arm composed of the fourth resistor and the eighth resistor of the negative phase signal voltage divider resistor, an upper bridge arm composed of the fifth resistor and the ninth resistor of the positive phase signal voltage divider resistor, a lower bridge arm composed of the thirteenth resistor and the sixteenth resistor of the negative phase signal voltage divider resistor, and a lower bridge arm composed of the fourteenth resistor and the seventeenth resistor of the positive phase signal voltage divider resistor.

[0020] Preferably, the operational amplifier circuit is a buffer structure consisting of a first operational amplifier and a second operational amplifier, the non-inverting input terminal of the first operational amplifier is connected between the eighth resistor and the thirteenth resistor, the non-inverting input terminal of the second operational amplifier is connected between the ninth resistor and the fourteenth resistor, and the inverting input terminal and output terminal of the first operational amplifier and the inverting input terminal and output terminal of the second operational amplifier are all connected to the signal output terminal via a third RC filter circuit.

[0021] The output end of the DC-DC isolated power supply is also connected to the input end of the low voltage difference linear regulator, and the output end of the low voltage difference linear regulator is connected to the input end of the isolation amplifier.

[0022] Parameter design system for isolation circuits for bridge sensors, including:

[0023] The sensor parameter input module is used to obtain the original excitation source output voltage, full-scale output voltage and bridge impedance data of the bridge sensor;

[0024] An isolation amplifier parameter calculation module is used to calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters;

[0025] The bridge voltage divider and voltage reference proportional parameter configuration module is used to determine the required voltage divider ratio and the output voltage value of the voltage reference circuit in combination with the proportional restoration requirements. It also calculates and configures the parameters of the bridge voltage divider resistor network based on the voltage divider ratio to meet the buffer input conditions and isolated output consistency requirements;

[0026] The buffer parameter calculation module is used to determine the buffer's input offset voltage, temperature drift, and CMRR performance indicators based on system accuracy requirements and common-mode rejection ratio;

[0027] A filter parameter matching module is used to design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics;

[0028] The anti-interference parameter analysis module is used to estimate the common-mode voltage and calculate the common-mode rejection ratio, providing parameter basis for isolation amplifier selection and voltage divider resistor network design.

[0029] A method for designing a parameter design system for an isolation circuit for a bridge sensor includes the following steps:

[0030] S1. Obtain the excitation voltage, output voltage and bridge impedance data of the bridge sensor;

[0031] S2. Calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters;

[0032] S3. Determine the required voltage divider ratio and the output voltage value of the voltage reference circuit based on the fixed gain, target output range, and ratio restoration requirements;

[0033] S4. Calculate and configure parameters of the bridge voltage divider resistor network and the voltage reference circuit based on the voltage divider ratio determined in step S3 and the output voltage value of the voltage reference circuit to ensure that they match the buffer input and meet the proportional restoration requirement;

[0034] S5. Determine the input offset voltage, temperature drift, and CMRR performance indicators of the buffer based on the system accuracy requirements and common-mode rejection ratio;

[0035] S6. Design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics.

[0036] Preferably, the common-mode interference parameters in step S2 include instantaneous rate of change of current, common-mode voltage, fixed gain and common-mode rejection ratio;

[0037] Among them, the instantaneous rate of change of current The calculation formula is as follows:

[0038] (3);

[0039] Where, Indicates the peak load current when the thyristor is turned on, in A; Indicates the current rise time, in seconds; Indicates time;

[0040] Common-mode voltage The calculation formula is as follows:

[0041] (4);

[0042] Where, Indicates the ground wire inductance, unit is H;

[0043] Fixed gain The calculation formula is as follows:

[0044] (5);

[0045] Where, Indicates the target output voltage of the signal output terminal, in V;

[0046] The common mode rejection ratio is calculated as follows:

[0047] (6);

[0048] Where, represents the differential mode gain.

[0049] Preferably, in step S3, the amplification factor of the isolation amplifier is , the output voltage value of the voltage reference circuit and the original excitation source output voltage Substituting into formula (1) we can get the voltage divider ratio ;

[0050] In step S4, first, the output voltage value of the voltage reference circuit determined in step S3 is , configure the voltage reference circuit, and then determine its reference voltage by selecting the controllable precision voltage regulator model , and finally the reference voltage and the output voltage value of the voltage reference circuit Substituting into formula (2) we get and value.

[0051] Therefore, the present invention adopts the above-mentioned isolation circuit, parameter design system and design method for bridge sensor, which has the following beneficial effects:

[0052] 1. Precision signal amplification and conditioning: The weak differential signal (e.g., ±30mV) of the bridge sensor is isolated and amplified through the fixed gain of the isolation amplifier. Simultaneously, a voltage-divider resistor network (dual resistor design for the upper and lower bridge arms) is used to precisely match the target output range (e.g., ±1.23V). A symmetrical design reduces the impact of temperature drift, improving voltage-divider accuracy to ±0.1%, resolving the issue of single resistors being unable to meet required accuracy requirements. This ensures the accuracy of signal amplitude conditioning and avoids nonlinear distortion introduced by software secondary processing. Simultaneously, a voltage-divider resistor network (dual resistor design for the upper and lower bridge arms) is used to precisely match the target output range (e.g., ±1.23V). A symmetrical design reduces the impact of temperature drift, improving voltage-divider accuracy to ±0.1%, resolving the issue of single resistors being unable to meet required accuracy requirements and ensuring the accuracy of signal amplitude conditioning.

[0053] 2. Strong anti-interference capability: (1) Common-mode interference suppression: By calculating the common-mode voltage and common-mode rejection ratio, select isolation amplifiers (such as AMC1302) and buffers (such as OPA2189) with high CMRR to block common-mode interference such as ground loops and space radiation to ensure signal purity; (2) Multi-stage filtering design: Input side magnetic beads + RC filtering, RC filtering after voltage division, and output side LC filtering work together to cover interference frequency bands such as high-frequency common-mode noise (magnetic beads) and low-frequency ripple (LC), building a full-link anti-interference barrier;

[0054] 3. Adaptability and integration (1) Modular design: The power supply part (DC-DC isolated power supply, voltage reference circuit) and the signal part (isolation amplifier, filter network) are independently scalable, which is convenient for embedding different bridge sensor systems (such as strain gauges, pressure sensors) and adapting to the needs of multiple scenarios such as industry and medical care; (2) Universal device selection: Standard devices (AMC1302, OPA2189, TL431) are used to reduce procurement and replacement costs; voltage divider resistors and filter elements use conventional resistance / capacitance values, which reduces the difficulty of engineering implementation.

[0055] 4. High precision and long-term stability: (1) Low-distortion signal chain: The low input offset voltage (±1μV) and low temperature drift (±0.2μV / °C) of the buffer (OPA2189), combined with the linear amplification characteristics of the isolation amplifier, ensure that the signal distortion is less than 0.5%FS, meeting the requirements of high-precision measurement; (2) Power supply stability support: The voltage reference circuit (TL431) provides an excitation voltage with an accuracy of ±0.5%, and the DC-DC isolation power supply cuts off interference on the power supply side, ensuring the long-term stability of the bridge sensor reference voltage and avoiding measurement errors caused by power supply fluctuations.

[0056] In summary, the present invention realizes high-precision, high-reliability, and anti-interference isolated transmission of bridge sensor signals through the full-link design of "signal amplification → anti-interference suppression → precise conditioning → stable power supply", which not only solves the noise pollution problem in industrial environments, but also ensures the long-term stability and measurement accuracy of the system, and adapts to the needs of multi-scenario engineering. Moreover, the isolator only needs to be connected in series to the circuit to achieve proportional isolation, which is plug-and-play and does not require any modifications to the program or hardware, making it easy to operate.

[0057] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a structural block diagram of the isolation circuit for the bridge sensor of the present invention;

[0059] Figure 2 This is a circuit schematic diagram of the isolation circuit for the bridge sensor of the present invention;

[0060] Figure 3 This is a force control curve diagram of a test bench force control system according to an embodiment of the present invention due to the interference of silicon controlled heating.

[0061] Figure 4 This is a force control curve diagram of a test bench force control system described in an embodiment of the present invention, which has the isolation module added and can enable SCR heating. DETAILED DESCRIPTION

[0062] In order to make the purposes, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0063] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0064] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0065] like Figure 1 and Figure 2 As shown, the isolation circuit for a bridge sensor includes a power supply part and a signal part, wherein the power supply part includes a power supply, a protection circuit, a first RC filter circuit, a DC-DC isolation power supply, a voltage reference circuit and an excitation source connected in series; the signal part includes a signal input terminal, a magnetic bead filter circuit, a second RC filter circuit, an isolation amplifier, a voltage divider resistor network, an operational amplifier circuit, a third RC filter circuit and a signal output terminal connected in series; the DC-DC isolation power supply is used to convert the voltage input through the power supply into two isolated outputs, one of which supplies power to the voltage reference circuit, and the other supplies power to the isolation amplifier after being stepped down by a low-voltage difference linear regulator, which isolates and boosts the input 5V power supply to 9V.

[0066] Specifically, the voltage divider resistor network consists of an upper bridge arm and a lower bridge arm, which is used to divide the amplified signal according to the voltage divider ratio. Reduction; The voltage reference circuit includes a controllable precision voltage regulator. In this embodiment, a TL431 controllable precision voltage regulator is selected. The K electrode of the controllable precision voltage regulator is respectively connected to one end of the first resistor R1 and the base of the transistor Q1. The other end of the first resistor R1 and the collector of the transistor Q1 are both connected to the output end of the DC-DC isolated power supply. The emitter of the transistor Q1 is respectively connected to one end of the second resistor R2 and the excitation source. The other end of the second resistor R2 is connected in series with the third resistor R3 and then grounded. The second resistor R2 and the third resistor R3 are connected to the R electrode of the controllable precision voltage regulator via a lead. The A electrode of the controllable precision voltage regulator is grounded.

[0067] And the output voltage of the voltage reference circuit and the excitation source voltage of the original bridge sensor The following proportional relationship is satisfied:

[0068] (1);

[0069] in,

[0070] (2);

[0071] Where, Indicates the amplification factor of the isolation amplifier, and Represent the resistance values ​​of the first resistor and the second resistor respectively, Indicates the reference voltage of the controllable precision voltage regulator. When the TL431 controllable precision voltage regulator is selected, .

[0072] The voltage-divider resistor network includes an upper bridge arm composed of the fourth resistor R4 and the eighth resistor R8 of the negative phase signal voltage-divider resistor, an upper bridge arm composed of the fifth resistor R5 and the ninth resistor R9 of the positive phase signal voltage-divider resistor, a lower bridge arm composed of the thirteenth resistor R13 and the sixteenth resistor R16 of the negative phase signal voltage-divider resistor, and a lower bridge arm composed of the fourteenth resistor R14 and the seventeenth resistor R17 of the positive phase signal voltage-divider resistor.

[0073] The op amp circuit is a buffer structure consisting of a first operational amplifier and a second operational amplifier. The non-inverting input of the first operational amplifier is connected between the eighth resistor R8 and the thirteenth resistor R13, while the non-inverting input of the second operational amplifier is connected between the ninth resistor R9 and the fourteenth resistor R14. The inverting input and output of the first operational amplifier, as well as the inverting input and output of the second operational amplifier, are connected to the signal output terminal via a third RC filter circuit. Both the first and second operational amplifiers are OPA2189s, which feature a zero-drift architecture, extremely low input offset voltage (better than ±1μV), high common-mode rejection ratio (CMRR>120dB), and unity-gain stability. They provide low-noise, highly linear buffered outputs, ensuring signal reproduction accuracy and system compatibility.

[0074] The protection circuit includes a discharge tube TV1 and a transient suppression diode D1 connected in series at both ends of the power supply; the first RC filter circuit includes an inductor L4 connected to the positive electrode of the power supply at one end and a capacitor C25, one plate of the capacitor C25 is connected to the other end of the inductor, and the other plate of the capacitor C25 is grounded;

[0075] The isolation amplifier uses AMC1302 isolation amplifier. , used to amplify the input signal by 41 times the differential mode gain and electrically isolate it. It is based on a capacitive isolation architecture and has a fixed gain (typical value of about 41 times), high common mode transient immunity ( ), low temperature drift and other characteristics, suitable for stably amplifying millivolt-level differential signals in a strong electromagnetic interference environment; the output end of the DC-DC isolated power supply is also connected to the input end of the low-voltage dropout linear regulator, and the output end of the low-voltage dropout linear regulator is connected to the input end of the isolation amplifier.

[0076] Parameter design system for isolation circuits for bridge sensors, including:

[0077] The sensor parameter input module is used to obtain the original excitation source output voltage, full-scale output voltage and bridge impedance data of the bridge sensor;

[0078] An isolation amplifier parameter calculation module is used to calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters;

[0079] The bridge voltage divider and voltage reference proportional parameter configuration module is used to determine the required voltage divider ratio and the output voltage value of the voltage reference circuit in combination with the proportional restoration requirements. It also calculates and configures the parameters of the bridge voltage divider resistor network based on the voltage divider ratio to meet the buffer input conditions and isolated output consistency requirements;

[0080] The buffer parameter calculation module is used to determine the buffer's input offset voltage, temperature drift, and CMRR performance indicators based on system accuracy requirements and common-mode rejection ratio;

[0081] A filter parameter matching module is used to design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics;

[0082] The anti-interference parameter analysis module is used to estimate the common-mode voltage and calculate the common-mode rejection ratio, providing parameter basis for isolation amplifier selection and voltage divider resistor network design.

[0083] A method for designing a parameter design system for an isolation circuit for a bridge sensor includes the following steps:

[0084] S1. Obtain the excitation voltage, output voltage and bridge impedance data of the bridge sensor;

[0085] S2. Calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters;

[0086] The common-mode interference parameters described in step S2 include instantaneous rate of change of current, common-mode voltage, fixed gain, and common-mode rejection ratio;

[0087] Among them, the instantaneous rate of change of current The calculation formula is as follows:

[0088] (3);

[0089] Where, Indicates the peak load current when the thyristor is turned on, in A; Indicates the current rise time, in seconds; Indicates time;

[0090] Common-mode voltage The calculation formula is as follows:

[0091] (4);

[0092] Where, Indicates the ground wire inductance, unit is H;

[0093] Fixed gain The calculation formula is as follows:

[0094] (5);

[0095] Where, Indicates the target output voltage of the signal output terminal, in V;

[0096] The common mode rejection ratio is calculated as follows:

[0097] (6);

[0098] Where, represents the differential mode gain.

[0099] S3. Determine the required voltage divider ratio and the output voltage value of the voltage reference circuit based on the fixed gain, target output range, and ratio restoration requirements;

[0100] In step S3, the amplification factor of the isolation amplifier is set to , the output voltage value of the voltage reference circuit and the original excitation source output voltage Substituting into formula (1) we can get the voltage divider ratio ;

[0101] S4. Calculate and configure parameters of the bridge voltage divider resistor network and the voltage reference circuit based on the voltage divider ratio determined in step S3 and the output voltage value of the voltage reference circuit to ensure that they match the buffer input and meet the proportional restoration requirement;

[0102] In step S4, first, the output voltage value of the voltage reference circuit determined in step S3 is , configure the voltage reference circuit, and then determine its reference voltage by selecting the controllable precision voltage regulator model , and finally the reference voltage And the output voltage value of the voltage reference circuit Substituting into formula (2) we get and value.

[0103] S5. Determine the input offset voltage, temperature drift, and CMRR performance indicators of the buffer based on the system accuracy requirements and common-mode rejection ratio;

[0104] S6. Design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics.

[0105] Example

[0106] In an industrial environment, a bridge pressure sensor (strain gauge bridge) needs to collect its output differential signal. The requirements are: the full-scale output of the sensor is 30mV, and the system measurement accuracy is required to be ±0.5%, that is, ±150µV. According to the system accuracy requirement of ±0.5%FS, in order to reserve a safety margin, the design target error limit is set to ±75μV, that is, µV.

[0107] First, we know from the data sheet that the maximum heating current of the heating wire , refer to the thyristor power regulator data sheet to get the current rise time μs, the current change rate formula is:

[0108] ;

[0109] According to the characteristics of the test bench, estimate >2µH. The minimum common-mode voltage is obtained as:

[0110] ;

[0111] get:

[0112] ;

[0113] Then we get:

[0114] ;

[0115] It can be seen that the common-mode suppression requirements mentioned above exceed the capabilities of conventional differential amplifier circuits and filtering topologies, making it difficult for non-isolated architectures to effectively suppress this type of interference. Therefore, high-isolation signal isolation devices are required to physically cut off the transmission paths of common-mode interference, such as sudden ground potential changes, to ensure measurement signal accuracy and system stability.

[0116] In order to solve the above problems, the isolation circuit of the present invention is added. In order to verify its practical application effect, the isolation circuit of the present invention is actually tested to solve the interference of the thyristor heating causing the force control instability of the force control test bench. The results are as follows: Figure 3 and Figure 4 As shown, it can be seen that the interference phenomenon has been eliminated, and the isolation circuit effectively isolates the interference signal introduced by the heating system, verifying the good anti-interference performance of the present invention in practical applications.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. Isolation circuit for bridge type sensor, characterized by: It includes a power supply part and a signal part, wherein the power supply part includes a power supply, a protection circuit, a first RC filter circuit, a DC-DC isolation power supply, a voltage reference circuit and an excitation source connected in series in sequence; The signal part includes a signal input terminal, a magnetic bead filter circuit, a second RC filter circuit, an isolation amplifier, a voltage divider resistor network, an operational amplifier circuit, a third RC filter circuit and a signal output terminal connected in series in sequence; The DC-DC isolated power supply is used to convert the voltage input from the power supply into two isolated outputs. One output is used to power the voltage reference circuit, and the other output is used to power the isolation amplifier after being stepped down by a low-dropout linear regulator. The voltage divider resistor network consists of an upper bridge arm and a lower bridge arm, which is used to divide the amplified signal according to the voltage divider ratio. reduction; The voltage reference circuit includes a controllable precision voltage-stabilizing source, wherein the K electrode of the controllable precision voltage-stabilizing source is respectively connected to one end of a first resistor and the base of a transistor, the other end of the first resistor and the collector of the transistor are both connected to the output end of a DC-DC isolated power supply, the emitter of the transistor is respectively connected to one end of a second resistor and an excitation source, the other end of the second resistor is connected in series with a third resistor and then grounded, the second resistor and the third resistor are connected to the R electrode of the controllable precision voltage-stabilizing source via a lead, and the A electrode of the controllable precision voltage-stabilizing source is grounded; And the output voltage of the voltage reference circuit , the original excitation source output voltage and voltage divider ratio The following relationship is satisfied: （1）； in, （2）； Where, Indicates the amplification factor of the isolation amplifier, and Represent the resistance values ​​of the first resistor and the second resistor respectively, Indicates the reference voltage of the controllable precision voltage regulator; The voltage-divider resistor network includes an upper bridge arm formed by the fourth resistor and the eighth resistor of the negative phase signal voltage-divider resistor, an upper bridge arm formed by the fifth resistor and the ninth resistor of the positive phase signal voltage-divider resistor, a lower bridge arm formed by the thirteenth resistor and the sixteenth resistor of the negative phase signal voltage-divider resistor, and a lower bridge arm formed by the fourteenth resistor and the seventeenth resistor of the positive phase signal voltage-divider resistor.

2. The isolation circuit for a bridge sensor according to claim 1, wherein: The operational amplifier circuit is a buffer structure consisting of a first operational amplifier and a second operational amplifier. The non-inverting input terminal of the first operational amplifier is connected between the eighth resistor and the thirteenth resistor, the non-inverting input terminal of the second operational amplifier is connected between the ninth resistor and the fourteenth resistor, and the inverting input terminal and output terminal of the first operational amplifier and the inverting input terminal and output terminal of the second operational amplifier are all connected to the signal output terminal via the third RC filter circuit.

3. The isolation circuit for a bridge sensor according to claim 2, wherein: The output end of the DC-DC isolated power supply is also connected to the input end of the low voltage difference linear regulator, and the output end of the low voltage difference linear regulator is connected to the input end of the isolation amplifier.

4. The parameter design system for the isolation circuit for a bridge sensor according to claim 3, characterized in that: include: The sensor parameter input module is used to obtain the original excitation source output voltage, full-scale output voltage and bridge impedance data of the bridge sensor; An isolation amplifier parameter calculation module is used to calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters; The bridge voltage divider and voltage reference proportional parameter configuration module is used to determine the required voltage divider ratio and the output voltage value of the voltage reference circuit in combination with the proportional restoration requirements. It also calculates and configures the parameters of the bridge voltage divider resistor network based on the voltage divider ratio to meet the buffer input conditions and isolated output consistency requirements; The buffer parameter calculation module is used to determine the buffer's input offset voltage, temperature drift, and CMRR performance indicators based on system accuracy requirements and common-mode rejection ratio; A filter parameter matching module is used to design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics; The anti-interference parameter analysis module is used to estimate the common-mode voltage and calculate the common-mode rejection ratio, providing parameter basis for isolation amplifier selection and voltage divider resistor network design.

5. A design method for a parameter design system for an isolation circuit for a bridge sensor according to claim 4, characterized in that: The following steps are involved: S1. Obtain the excitation voltage, output voltage and bridge impedance data of the bridge sensor; S2. Calculate common-mode interference parameters based on the excitation voltage and bridge impedance data, and determine the amplification factor of the isolation amplifier according to the common-mode interference parameters; S3. Determine the required voltage divider ratio and the output voltage value of the voltage reference circuit based on the fixed gain, target output range, and ratio restoration requirements; S4. Calculate and configure parameters of the bridge voltage divider resistor network and the voltage reference circuit based on the voltage divider ratio determined in step S3 and the output voltage value of the voltage reference circuit to ensure that they match the buffer input and meet the proportional restoration requirement; S5. Determine the input offset voltage, temperature drift, and CMRR performance indicators of the buffer based on the system accuracy requirements and common-mode rejection ratio; S6. Design parameters of the first RC filter circuit, the second RC filter circuit, and the third RC filter circuit according to the signal bandwidth and interference frequency characteristics.

6. The method for designing a parameter design system for an isolation circuit for a bridge sensor according to claim 5, characterized in that: The common-mode interference parameters described in step S2 include instantaneous rate of change of current, common-mode voltage, fixed gain, and common-mode rejection ratio; Among them, the instantaneous rate of change of current The calculation formula is as follows: （3）； Where, Indicates the peak load current when the thyristor is turned on, in A; Indicates the current rise time, in seconds; Indicates time; Common-mode voltage The calculation formula is as follows: （4）； Where, Indicates the ground inductance, unit is H Fixed gain The calculation formula is as follows: （5）； Where, Indicates the target output voltage of the signal output terminal, in V; The common mode rejection ratio is calculated as follows: （6）； Where, represents the differential mode gain.

7. The method for designing a parameter design system for an isolation circuit for a bridge sensor according to claim 6, characterized in that: In step S3, the amplification factor of the isolation amplifier is set to , the output voltage value of the voltage reference circuit and the original excitation source output voltage Substituting into formula (1) we can get the voltage divider ratio ; In step S4, first, the output voltage value of the voltage reference circuit determined in step S3 is , configure the voltage reference circuit, and then determine its reference voltage by selecting the controllable precision voltage regulator model , and finally the reference voltage And the output voltage value of the voltage reference circuit Substituting into formula (2) we get and value.

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