Weak signal acquisition system based on frequency adaptive technology

Abstract

This invention discloses a weak signal acquisition system based on frequency adaptive technology, relating to the field of mass flow meter measurement. The invention includes a balun network module, an integrated digital temperature compensation chip, and a frequency-adaptive phase-locked loop; an MCU for acquiring the current frequency and temperature, feeding forward to adjust the variable gain amplifier and variable phase-shift network; the MCU also works in conjunction with the balun differential-mode power input to adjust the gain and phase in a closed loop, ensuring consistent output power between the two channels; a pre-defined anti-slope compensation table for parasitic asymmetry and temperature rise loss obtained through electromagnetic simulation and calibration, stored as a two-dimensional lookup table for adjustment; and a synchronous ADC for acquisition, obtaining the phase difference to achieve weak signal acquisition. This invention significantly improves inter-channel phase consistency, while also possessing temperature drift suppression capabilities, high long-term operational stability, and high signal fidelity.

Description

Technical Field

[0001] This invention relates to the field of mass flow meter measurement, and more specifically to a weak signal acquisition system based on frequency adaptive technology. Background Technology

[0002] Mass flow meters calculate mass flow rate by detecting the phase difference between the sinusoidal signals output by two sensor coils. The performance of the front-end acquisition and amplification circuit directly determines the fidelity of the phase difference signal.

[0003] Traditional solutions typically use fixed-gain amplifiers to symmetrically amplify the two signals before an analog-to-digital converter (ADC) samples them and calculates the phase difference. To eliminate channel mismatch, a one-time static gain and phase matching calibration is often performed at the factory. However, in practical applications, the following significant shortcomings exist:

[0004] Firstly, the winding of the sensor coil itself, the PCB traces, and the connectors can introduce tiny asymmetric parasitic parameters, resulting in a fixed or slowly changing phase shift between the two channels, which cannot be eliminated by factory static matching alone.

[0005] Secondly, when the flow meter operates continuously over a wide temperature range for a long time, device aging and environmental stress will introduce a slow phase drift. The open-loop fixed amplification structure lacks the ability to sense and dynamically compensate for this type of drift in real time, which severely limits the long-term measurement accuracy.

[0006] Therefore, there is an urgent need for a front-end signal conditioning scheme that can identify and compensate for residual parasitic asymmetry and long-term aging drift in real time. Summary of the Invention

[0007] This invention provides a weak signal acquisition system based on frequency adaptive technology, which solves the problems of existing technologies.

[0008] In a first aspect, the present invention provides a weak signal acquisition system based on frequency adaptive technology, comprising:

[0009] A balun network module that performs balanced-to-unbalanced conversion on the dual-channel pickup coil signal of the flow meter sensor and obtains differential mode power; an integrated digital temperature compensation chip for real-time sensing of the front-end temperature field; and a frequency-adaptive phase-locked loop.

[0010] The MCU is used to obtain the current frequency and temperature, feedforward adjust the variable gain amplifier and variable phase shift network. The MCU is also used to cooperate with the balun differential mode power introduction closed loop adjustment of gain and phase to keep the output power of the two channels consistent.

[0011] The adjustment of gain and phase includes obtaining a reverse slope compensation table for parasitic asymmetry and temperature rise loss in advance through electromagnetic simulation and calibration, storing it as a two-dimensional lookup table, and making adjustments by looking up the table.

[0012] Synchronous ADCs are used for acquisition, and the phase difference is used to acquire weak signals.

[0013] Furthermore, the MCU used to acquire the current frequency and temperature, and to feedforward adjust the variable gain amplifier and variable phase shift network, is also used to coordinate with the balun differential mode power introduction closed-loop adjustment of gain and phase to keep the output power of the two channels consistent, including:

[0014] Electromagnetic simulation software was used to extract parasitic inductance, capacitance, and coupling parameters of PCB traces, connectors, and coil leads. A dual-channel SPICE model was established, and the temperature was scanned within the range of -40°C to +85°C. The device temperature drift model was superimposed, and the frequency response of H1 and H2 was simulated. The gain difference ΔA(ω,T) and the additional phase shift Δθ(ω,T) were calculated, and the inverse slope compensation tables CG and Cθ were generated. The data were compressed and stored in the MCU Flash using two-dimensional cubic spline interpolation or polynomial fitting. H1 and H2 are the transfer functions of the two pickup coil channels and are affected by the frequency ω and temperature T.

[0015] Furthermore, the anti-slope compensation table for parasitic asymmetry and temperature rise loss, obtained in advance through electromagnetic simulation and calibration, is stored as a two-dimensional lookup table. Adjustments are made by looking up the table, including:

[0016] ;

[0017] These are the inverse slope compensation functions for the gain difference characteristic and the phase difference characteristic, respectively.

[0018] Wherein, the gain difference is ΔA = |H1 / H2|, and the additional phase shift is Δθ = arg(H1) - arg(H2).

[0019] Regarding transfer functions:

[0020] The front-end equivalent input network of the i-th channel can be simplified to a combination of series inductance, parallel capacitance, and contact resistance, i=1,2; the parasitic parameters mainly include series inductance Lsi, parallel capacitance Cpi, and connector contact resistance Rci. At frequency ω, the channel transfer function is:

[0021] ;

[0022] Where Ki is the DC or intermediate frequency gain coefficient of the i-th channel;

[0023] Rci: Connector contact resistance and the equivalent resistance of the trace in series. The resistance and the subsequent parallel capacitor together form a low-pass pole, introducing frequency-related phase shift and attenuation.

[0024] Cpi: Parallel parasitic capacitance, including PCB pads, traces to ground distributed capacitance, and amplifier input capacitance; together with Rci and Lsi, it forms a second-order network;

[0025] Lsi: Series parasitic inductance, which originates from the inductive effect of sensor coil leads, PCB traces and connector pins, and can cause resonance and additional phase lag at high frequencies;

[0026] τi is the pure delay time or trace delay of the channel, including the signal propagation delay caused by the physical length of the PCB trace, and the resulting phase difference between channels:

[0027] exponent e- jωτi This indicates the linear phase lag caused by the pure delay;

[0028] Gain difference:

[0029] ;

[0030] Phase difference:

[0031] ;

[0032] Temperature characteristics of contact resistance Rci:

[0033] ;

[0034] Where Rci0: nominal contact resistance at reference temperature T0; α R Temperature coefficient of resistance;

[0035] Temperature characteristics of parallel capacitor Cpi:

[0036] ;

[0037] Where Cpi0: nominal parasitic capacitance at reference temperature; α C Temperature coefficient of capacitor;

[0038] Temperature characteristics of series inductor Lsi:

[0039] ;

[0040] Where Lsi0: nominal inductance at the reference temperature; α L Temperature coefficient of inductance;

[0041] Amplifier gain, i.e., intermediate frequency gain coefficient, and trace delay are considered constants in a narrow temperature range.

[0042] Furthermore, it specifically includes: a front-end signal interface and a balun network module, wherein the sensor coil output is connected to a 1:1 center-tapped balun, which converts the two differential signals into single-ended signals respectively, and simultaneously generates a sum signal and a difference signal. The sum and difference ports of the balun's secondary output are connected to a true RMS power detector to obtain the sum signal power Psum and the difference signal power Pdiff. The two main signal paths are led out from another pair of balanced outputs of the balun and enter a pre-amplifier with variable gain. Specifically:

[0043] The flow meter's dual-channel pickup coil outputs a pair of sinusoidal signals of the same frequency;

[0044] Supplementing information regarding power consistency and feedback control law, the two outputs after compensation:

[0045] ;

[0046] ;

[0047] Where V1(t) and V2(t) are the two compensated signals finally fed into the second balun and the subsequent ADC, respectively. The original output signal amplitudes of the two pickup coils are A1 and A2, respectively, and their initial phases are respectively... 1. 2. The frequency is ω. G1 and G2 are the total equivalent gains of the two channels. θ1 and θ2 are the additional phases artificially introduced into the two channels by adjustable phase shifters. The control system compensates for the inherent parasitic additional phase shifts between channels by adjusting θ1 and / or θ2, so that, except for the flow phase Δ... Apart from that, there is no further phase shift;

[0048] The error characteristics are fed forward into the programmable compensation network, and the two signals are combined into a sum signal and a difference signal using a balun network module.

[0049] And the signal Vsum = V1 + V2;

[0050] Difference signal Vdiff = V1 - V2;

[0051] ;

[0052] Differential signal power A closed loop is formed with the goal of minimizing Pdiff, which is used to track and compensate for drift in real time.

[0053] Furthermore, it includes: a temperature and frequency sensing module equipped with a digital temperature compensation chip, used to acquire the front-end temperature and signal frequency in real time, providing input parameters for the compensation model; the digital temperature compensation chip sends the temperature value to the MCU via I²C.

[0054] Furthermore, for the frequency adaptive variable gain / phase compensation module including the phase-locked loop, it is used to adjust the channel gain and phase shift in real time according to the frequency adaptive feedforward compensation value, in conjunction with closed-loop fine-tuning; take one of the amplified signals and convert it into a square wave through a zero comparator, use the MCU timer to measure the period, or use the phase-locked loop to generate a frequency word, and use the frequency measurement result as the input of the frequency adaptive controller.

[0055] A frequency-adaptive phase-locked loop is used to ensure that the compensation network and filtering characteristics operate at the signal frequency when the sensor resonant frequency changes with the operating conditions during the compensation process. This includes a variable gain amplifier, a variable phase shift network, and a bandpass filter for frequency-adaptive filtering.

[0056] Furthermore, the MCU is also used to coordinate with the balun differential power input closed-loop adjustment of gain and phase to ensure that the output power of the two channels remains consistent, specifically including:

[0057] At the outputs of the VGA and phase-shifting network, the difference signal power Pdiff is extracted again through a balun. The MCU has a built-in incremental PID controller with the input being the normalized power error e=(Pdiff-Pref) and the target being Pref=0. The PID outputs finely adjust the VGA gain and the phase-shifting control word, respectively. The feedforward value serves as the reference bias for the PID controller, and the closed loop is responsible for correcting slow drift and model error.

[0058] Furthermore, the specific calculation method for the inverse slope compensation function includes:

[0059] By obtaining Δθk,m and ΔAk,m on the discrete grid (ωk,Tm) through simulation or calibration, an inverse slope compensation is constructed:

[0060] ;

[0061] Data compression was achieved using bivariate polynomial regression:

[0062] ;

[0063] The coefficients aij were obtained through least squares fitting and written into the MCU.

[0064] Furthermore, the coefficients aij are obtained through least squares fitting, specifically including:

[0065] Calculate or measure the gain difference ΔAk,m and phase difference Δθk,m at the grid points using electromagnetic simulation software;

[0066] Construct a polynomial model with frequency order M and temperature order N. Each data point corresponds to an equation. Write the equations for all grid points in matrix form: Y = Xa, where Y is a column vector consisting of all ΔA or Δθ observations, and X is the design matrix with each row in [1, ω, T, ω 2 ,ωT,T 2 ,…],a:The coefficient vector aij to be fitted, and the least squares solution is obtained.

[0067] The weak signal acquisition system based on frequency adaptive technology provided by this invention significantly improves the phase consistency between channels, while also having temperature drift suppression capability, long-term operational stability, and high signal fidelity; the signal-to-noise ratio is improved, and it has frequency adaptive dynamic tracking capability. Attached Figure Description

[0068] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, are not intended to limit the scope of the invention. In the drawings:

[0069] Figure 1 The overall structure diagram of a weak signal acquisition system based on frequency adaptive technology provided for an exemplary embodiment of the present invention is shown.

[0070] Figure 2 The present invention provides a balun and differential power detection circuit structure in a weak signal acquisition system based on frequency adaptive technology, which is an exemplary embodiment of the present invention.

[0071] Figure 3 This is an analog signal conditioning and frequency adaptive filtering chain diagram in a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention.

[0072] Figure 4 A diagram showing the digital control loop and feedforward compensation structure in a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention. Detailed Implementation

[0073] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention.

[0074] Technical concept of the present invention:

[0075] The core of this invention lies in "marking" the asymmetric errors in the two physical measurement channels using a known, ideally balanced reference signal, thereby transforming the problem of measuring the "relative" error between channels into the problem of measuring the "absolute" phase delay on each channel independently.

[0076] The weak signal acquisition system based on frequency adaptive technology provided by this invention aims to solve the above-mentioned technical problems of the prior art.

[0077] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0078] Example 1: The process of obtaining the phase difference in multiple steps is as follows:

[0079] The front-end signal interface and balun network module pick up the differential signals of the dual coils to achieve impedance matching and balanced-to-unbalanced conversion, and extract power error. The temperature and frequency sensing module acquires the front-end temperature and signal frequency in real time, providing input parameters for the compensation model. The channel mismatch curves are obtained across the entire temperature and frequency range, and a feedforward compensation lookup table is constructed to realize parasitic parameter pre-simulation and inverse slope compensation model establishment. The frequency adaptive variable gain / phase compensation module adjusts the channel gain and phase shift in real time according to the frequency adaptive feedforward compensation value, with closed-loop fine-tuning. The variable gain amplifier uses a low-noise, wide-bandwidth VGA (such as AD8331), and its gain is controlled by the MCU through a 12-bit DAC, covering the range of ±3 dB required for compensation. Variable phase-shift network: An all-pass filter built with operational amplifiers is used. The pole positions are adjusted via digital potentiometers or varactor diodes in conjunction with the DAC voltage to achieve fine phase adjustment. The group delay changes with frequency and is corrected by the MCU based on the current frequency. Frequency adaptive filtering: A bandpass filter with an adjustable center frequency is inserted before the ADC. A switched-capacitor filter (such as MAX263) or an LC filter tuned by a varactor diode is used, controlled by the same frequency word to always align with the signal frequency, eliminating harmonics and maintaining phase consistency of the dual-channel filters. The balun differential mode power is then used as an error indicator to close the loop and eliminate residual mismatch. The equalized dual-channel signals are digitized to calculate the precise phase difference. Includes: a dual-channel synchronous sampling 24-bit Σ-Δ ADC (such as ADS131M04), sampling rate 4 kSps, with built-in programmable gain to ensure amplitude matching. Digital quadrature demodulation: Quadrature references sin(ωn) and cos(ωn) with the same frequency as the signal are generated, multiplied by the two signals respectively, and low-pass filtered to obtain the I / Q components. The phase angle is then calculated. =arctan(Q / I), and finally calculate the phase difference between the two channels. The demodulation reference frequency is updated in real time by the frequency measurement value, realizing frequency adaptation.

[0080] The flow meter's dual-channel pickup coil outputs a pair of sinusoidal signals of the same frequency;

[0081] Supplementing information regarding power consistency and feedback control law, the two outputs after compensation:

[0082] ;

[0083] ;

[0084] Differential signal power:

[0085] ;

[0086] To minimize Pdiff, we need to let G1 = G2 and Δ Includes only flow phase. Define control error:

[0087] , so that cos(Δ Maximize the number of terms;

[0088] PID controller:

[0089] ;

[0090] Where, u(n) — the output value of the controller at the nth sampling time. In this system, this output is superimposed on the feedforward compensation and directly converted into digital codewords for the gain control DAC (or phase control DAC) to drive the VGA (or phase shifter); e(n) — the error signal at the nth sampling time. It is defined as the difference between the measured value and the expected value (usually zero) of the closed-loop differential power P2, i.e., e(n) = P2,ref - P2(n). When the amplitudes of the two signals are completely equal and the additional phase shift is fully compensated, P2 = 0, and the error is zero. n — discrete-time index, indicating the nth sampling and control cycle, usually corresponding to the PID calculation cycle of the MCU. Kp — proportional gain (dimensionless, or depending on the output / input units). The proportional term Kpe(n) directly produces an immediate correction effect based on the magnitude of the current error. The larger the error, the stronger the control output, causing the system to quickly adjust in the direction of reducing the error. Ki—Integral gain (unit: 1 / time, i.e., the accumulation rate per sampling period), mainly used to eliminate steady-state residual error. Even if the error is small, the integral effect will continue to accumulate until the error disappears completely. A large Ki may cause oscillation, while a small Ki will result in slow elimination of steady-state error. Kd—Derivative gain (unit: time). The derivative term Kd[e(n)-e(n-1)] reflects the trend of error change, which can suppress overshoot and speed up the response. When the error changes rapidly, the derivative term provides a damping effect; however, if the system noise is large, the derivative term may be amplified, requiring appropriate filtering or limitation. e(n-1)—The error value at the previous sampling time, used to calculate the change in error (difference).

[0091] The gain and phase control quantities are respectively superimposed with feedforward quantities Gctrl = Gcomp + uG, θctrl = θcomp + uθ; where n is the discrete sampling time number and the nth control period. The error at the current moment, The error from the previous moment is used to adjust the parameters.

[0092] ;

[0093] ;

[0094] Because the closed-loop bandwidth is extremely low, it will not affect the flow phase signal of tens to hundreds of hertz.

[0095] Mathematical model for generating frequency adaptive filters:

[0096] A second-order state-variable bandpass filter is used, with the center frequency ω0 set by an external control voltage Vf. Its transfer function is:

[0097] ;

[0098] Here, s is the complex frequency variable in the Laplace transform, defined as: Q is the quality factor;

[0099] The numerator s / ω0 indicates that the signal is suppressed at low frequencies and gradually enhanced at high frequencies, forming a bandpass characteristic. The denominator s2 / ω02 and s / (Qω0) determine the resonant peak value and bandwidth.

[0100] The first term in the denominator determines the damping ratio ζ = 1 / 2Q; the second term in the denominator determines the high-frequency roll-off.

[0101] By adaptively adjusting the frequency to make ω0 = ωsig, the phase responses of the two channel filters are ensured to be consistent.

[0102] ;

[0103] This avoids introducing additional phase shift. Vf is generated by a DAC from the frequency measurement, enabling real-time tracking.

[0104] Example 2: The overall processing procedure of the present invention is as follows:

[0105] The two differential signals output from pickup coils A and B first enter the first balun, completing the balanced-to-unbalanced conversion and simultaneously generating a differential-mode signal. The differential-mode signal is converted to DC level by the first RMS detector, characterizing the original amplitude and phase mismatch of the dual channels, and used by the MCU for initial state monitoring. The two single-ended signals are respectively sent to preamplifiers for fixed-gain amplification, boosting the signals to a level suitable for subsequent processing. Subsequently, the adjustable full-pass phase shifter and variable gain amplifier (VGA) are driven by the analog control voltage output from the MCU, independently applying anti-slope phase compensation and amplitude equalization to the dual channels. The compensation value comes from the superposition of two parts: one is a two-dimensional feedforward lookup table based on temperature sensors and frequency measurements, which has been pre-fitted with parasitic parameters and temperature drift characteristics through electromagnetic simulation and calibration, and is fixed in the MCU in the form of a binary polynomial; the other is the error signal output from the closed-loop feedback network composed of the second balun and the second RMS detector, which is calculated by the incremental PID controller in the MCU as a fine-tuning amount. The second balun resynthesizes the compensated dual signals and extracts the differential-mode power. This power is highly sensitive to any residual amplitude or phase mismatch, so minimizing its value ensures extremely high consistency in amplitude and additional phase shift between the two signals. After feedback adjustment, the two high-fidelity signals pass through a frequency-adaptive bandpass filter. The center frequency of this filter is constantly tuned by the MCU based on the real-time measured signal frequency, thus filtering out harmonics and noise while avoiding new errors introduced by inconsistent filter phase responses between the two channels. Subsequently, a 24-bit synchronous ADC synchronously converts the two signals into digital quantities at a 4 kSps sampling rate and sends them to the digital quadrature demodulation module. The quadrature local oscillator frequency used for demodulation is also updated in real-time by the MCU to ensure strict synchronization with the signal frequency and completely eliminate spectral leakage.

[0106] Finally, the demodulated I / Q components are used to obtain the instantaneous phase of each of the two channels through arctangent operation, and the difference between them yields the flow-related phase difference.

[0107] This embodiment includes three compensation lines:

[0108] 1. Feedforward compensation path (open loop)

[0109] Temperature sensor → MCU lookup table (inverse slope model) → Output phase compensation value and gain compensation value → Control phase shifter and VGA respectively.

[0110] Frequency measurement → MCU refreshes lookup table input, and simultaneously adjusts the center frequency of the bandpass filter.

[0111] 2. Closed-loop feedback path

[0112] Second balun differential mode power → Second RMS detector → MCU built-in PID → Fine-tuning phase shifter and VGA control input.

[0113] This loop has a bandwidth of only 0.1 Hz and is specifically designed to absorb slow drift and model residuals, making it transparent to dynamic flow signals.

[0114] 3. Measurement data path

[0115] Compensated dual-channel signal → Anti-aliasing filter → Synchronous ADC → Digital quadrature demodulation (reference frequency provided by MCU) → Phase difference output.

[0116] This path operates entirely under the protection of feedforward and closed loop, ensuring that the amplitude of the signal entering demodulation is consistent and that additional phase shift is eliminated.

[0117] The following sections will explain the overall structure separately:

[0118] like Figure 1 As shown, Figure 1 The overall system structure of a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention, is as follows: The differential signals from pickup coil A and pickup coil B are fed into a first balun, converting them into single-ended signals and extracting the differential-mode signal. The initial differential-mode power is obtained by a first RMS detector and sent to a microcontroller for status monitoring. The single-ended signals are amplified by preamplifiers A and B respectively, and then enter an adjustable phase shifter for phase pre-compensation. The amplitude is then independently adjusted by a first variable gain amplifier and a second variable gain amplifier. The compensated dual-channel signals are resynthesized by a second balun, and the differential-mode signal is converted into closed-loop error power by a second RMS detector and fed back to the microcontroller. The equalized signal is filtered for noise by a first frequency adaptive bandpass filter and a second frequency adaptive bandpass filter, and is synchronously acquired by a synchronous analog-to-digital converter. Finally, the phase difference is calculated in a digital quadrature demodulator. A temperature sensor provides the front-end temperature; one output of preamplifier A is connected to the microcontroller for frequency measurement. The microcontroller outputs phase control, gain control, frequency tuning, and demodulation reference frequency based on temperature, frequency, and power error signals, forming a complete closed loop.

[0119] like Figure 2 As shown, Figure 2The diagram illustrates the circuit structure of a balun and differential-mode power detection circuit in a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention. In the first-stage detection, pickup coils A and B are connected to a first balun. The differential-mode output D1 is sent to a first RMS detector, generating a DC signal P1 which is fed into the microcontroller's ADC, representing the original asymmetry. The single-ended output drives preamplifiers A and B, respectively. In the second-stage detection, the compensated signal is fed into a second balun by a first and a second variable gain amplifier. The differential-mode output D2 is converted to P2 by the second RMS detector and sent back to the microcontroller as closed-loop feedback. The equalized signal is then transmitted to a first and a second frequency adaptive bandpass filter, respectively.

[0120] like Figure 3 As shown, Figure 3 The diagram below illustrates an analog signal conditioning and frequency adaptive filtering chain in a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention. The outputs of preamplifiers A and B simultaneously enter an adjustable phase shifter, where an analog control voltage is provided by a phase-controlled digital-to-analog converter (DAC) to achieve dual-channel differential phase adjustment. The two phase-shifted signals are independently conditioned by a first variable gain amplifier and a second variable gain amplifier, with the gain voltage sourced from the gain-controlled DAC. The amplitude-equalized signal is then sent to a first frequency adaptive bandpass filter and a second frequency adaptive bandpass filter, whose center frequencies are synchronously controlled by the tuning voltage output from a frequency-tuned DAC, ensuring consistent filtering characteristics and consistent alignment with the signal frequency. Finally, the filtered signal is acquired by a synchronous analog-to-digital converter (ADC).

[0121] like Figure 4 As shown, Figure 4 This diagram illustrates the digital control loop and feedforward compensation structure in a weak signal acquisition system based on frequency adaptive technology, provided as an exemplary embodiment of the present invention. A temperature sensor and a frequency measurement module acquire real-time temperature and signal frequency, respectively, inputting them into a feedforward compensation lookup table and outputting gain compensation value G_comp and phase compensation value θ_comp as feedforward biases. The closed-loop differential mode power P2 provided by the second RMS detector serves as an error signal, entering the PID controller along with the feedforward value. After PID synthesis, the gain control quantity is output to the gain control digital-to-analog converter, the phase control quantity to the phase control digital-to-analog converter, and the frequency tuning quantity to the frequency tuning digital-to-analog converter, while a reference frequency word is sent to the digital quadrature demodulator. The control quantities ultimately act on the first variable gain amplifier, the second variable gain amplifier, the adjustable phase shifter, the first frequency adaptive bandpass filter, and the second frequency adaptive bandpass filter, forming a hierarchical control closed loop of "feedforward coarse adjustment + closed-loop fine calibration".

[0122] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0123] Furthermore, in the embodiments of the present invention, the functional modules can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated module can be implemented in hardware or in the form of hardware plus software functional modules.

[0124] Those skilled in the art will understand that embodiments of the present invention can be provided as methods or systems. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects.

[0125] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0126] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

[0127] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the invention disclosed herein in the specification and examples. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the foregoing claims.

[0128] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A weak signal acquisition system based on frequency adaptive technology, characterized in that, include: A balun network module that performs balanced-to-unbalanced conversion on the dual-channel pickup coil signal of the flow meter sensor and obtains differential mode power; an integrated digital temperature compensation chip for real-time sensing of the front-end temperature field; and a frequency-adaptive phase-locked loop. The MCU is used to obtain the current frequency and temperature, feedforward adjust the variable gain amplifier and variable phase shift network. The MCU is also used to cooperate with the balun differential mode power introduction closed loop adjustment of gain and phase to keep the output power of the two channels consistent. The adjustment of gain and phase includes obtaining a reverse slope compensation table for parasitic asymmetry and temperature rise loss in advance through electromagnetic simulation and calibration, storing it as a two-dimensional lookup table, and making adjustments by looking up the table. Synchronous ADCs are used for acquisition, and the phase difference is used to acquire weak signals.

2. The weak signal acquisition system based on frequency adaptive technology according to claim 1, characterized in that, The MCU used to acquire the current frequency and temperature, feedforward adjust the variable gain amplifier and variable phase shift network, and also to cooperate with the balun differential mode power introduction closed-loop adjustment of gain and phase to keep the output power of the two channels consistent, including: The electromagnetic simulation software is used to extract the parasitic inductance, capacitance and coupling parameters of PCB routing, connectors and coil leads, to establish a double-channel SPICE model, to scan the temperature in the range of -40°C to +85°C, to superimpose the device temperature drift model, to simulate the frequency response of H1 and H2, to calculate the gain difference ΔA(ω, T) and the additional phase shift Δθ(ω, T), and to generate the inverse slope compensation table C G With C θ and compressed and stored in the MCU Flash by using two-dimensional cubic spline interpolation or polynomial fitting, H1 and H2 being the transfer functions of the two-channel pickup coil channels and being affected by the frequency ω and the temperature T.

3. The weak signal acquisition system based on frequency adaptive technology according to claim 2, characterized in that, The anti-slope compensation table for parasitic asymmetry and temperature rise loss, obtained in advance through electromagnetic simulation and calibration, is stored as a two-dimensional lookup table. Adjustments are made by looking up the table, including: ； These are the inverse slope compensation functions for the gain difference characteristic and the phase difference characteristic, respectively. Wherein, the gain difference is ΔA = |H1 / H2|, and the additional phase shift is Δθ = arg(H1) - arg(H2). Regarding transfer functions: The front-end equivalent input network of the i-th channel can be simplified to a combination of series inductance, parallel capacitance, and contact resistance, i=1,2; the parasitic parameters mainly include series inductance Lsi, parallel capacitance Cpi, and connector contact resistance Rci. At frequency ω, the channel transfer function is: ； Where Ki is the DC or intermediate frequency gain coefficient of the i-th channel; Rci: Connector contact resistance and the equivalent resistance of the trace in series. The resistance and the subsequent parallel capacitor together form a low-pass pole, introducing frequency-related phase shift and attenuation. Cpi: Parallel parasitic capacitance, including PCB pads, traces to ground distributed capacitance, and amplifier input capacitance; together with Rci and Lsi, it forms a second-order network; Lsi: Series parasitic inductance, which originates from the inductive effect of sensor coil leads, PCB traces and connector pins, and can cause resonance and additional phase lag at high frequencies; τi is the pure delay time or trace delay of the channel, including the signal propagation delay caused by the physical length of the PCB trace, and the resulting phase difference between channels: exponent e- jωτi This indicates the linear phase lag caused by the pure delay; Gain difference: ； Phase difference: ； Temperature characteristics of contact resistance Rci: ； Where Rci0: nominal contact resistance at reference temperature T0; α R Temperature coefficient of resistance; Temperature characteristics of parallel capacitor Cpi: ； Where Cpi0: nominal parasitic capacitance at reference temperature; α C Temperature coefficient of capacitance; Temperature characteristics of series inductor Lsi: ； Where Lsi0: nominal inductance at the reference temperature; α L Temperature coefficient of inductance; Amplifier gain, i.e., intermediate frequency gain coefficient, and trace delay are considered constants in a narrow temperature range.

4. The weak signal acquisition system based on frequency adaptive technology according to claim 3, characterized in that, Specifically, it includes: a front-end signal interface and a balun network module, wherein the sensor coil output is connected to a 1:1 center-tapped balun, which converts the two differential signals into single-ended signals respectively, and simultaneously generates a sum signal and a difference signal. The sum and difference ports of the balun's secondary output are connected to a true RMS power detector to obtain the sum signal power Psum and the difference signal power Pdiff. The two main signal paths are led out from another pair of balanced outputs of the balun and enter a pre-amplifier with variable gain. Specifically: The flow meter's dual-channel pickup coil outputs a pair of sinusoidal signals of the same frequency; Supplementing information regarding power consistency and feedback control law, the two outputs after compensation: ； ； Where V1(t) and V2(t) are the two compensated signals finally fed into the second balun and the subsequent ADC, respectively. The original output signal amplitudes of the two pickup coils are A1 and A2, respectively, and their initial phases are respectively...

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2. The frequency is ω. G1 and G2 are the total equivalent gains of the two channels. θ1 and θ2 are the additional phases artificially introduced into the two channels by adjustable phase shifters. The control system compensates for the inherent parasitic additional phase shifts between channels by adjusting θ1 and / or θ2, so that, except for the flow phase Δ... Apart from that, there is no further phase shift; The error characteristics are fed forward into the programmable compensation network, and the two signals are combined into a sum signal and a difference signal using a balun network module. And the signal Vsum = V1 + V2; Difference signal Vdiff = V1 - V2; ； Differential signal power A closed loop is formed with the goal of minimizing Pdiff, which is used to track and compensate for drift in real time.

5. The weak signal acquisition system based on frequency adaptive technology according to claim 4, characterized in that, include: A temperature and frequency sensing module equipped with a digital temperature compensation chip is used to acquire the front-end temperature and signal frequency in real time, providing input parameters for the compensation model. The digital temperature compensation chip sends the temperature value to the MCU via I²C.

6. The weak signal acquisition system based on frequency adaptive technology according to claim 5, characterized in that, For the frequency adaptive variable gain / phase compensation module including phase-locked loop, it is used to adjust the channel gain and phase shift in real time according to the frequency adaptive feedforward compensation value, in conjunction with closed-loop fine-tuning; One of the amplified signals is converted into a square wave by a zero comparator. The period is measured using an MCU timer or a phase-locked loop is used to generate a frequency word. The frequency measurement result is used as the input of the frequency adaptive controller. A frequency-adaptive phase-locked loop is used to ensure that the compensation network and filtering characteristics operate at the signal frequency when the sensor resonant frequency changes with the operating conditions during the compensation process. This includes a variable gain amplifier, a variable phase shift network, and a bandpass filter for frequency-adaptive filtering.

7. The weak signal acquisition system based on frequency adaptive technology according to claim 6, characterized in that, The MCU is also used to coordinate with the balun differential mode power input closed-loop adjustment of gain and phase to ensure that the output power of the two channels remains consistent, specifically including: At the outputs of the VGA and phase-shifting network, the difference signal power Pdiff is extracted again through a balun. The MCU has a built-in incremental PID controller with the input being the normalized power error e=(Pdiff-Pref) and the target being Pref=0. The PID outputs fine-tune the VGA gain and the phase-shifting control word, respectively. The feedforward value serves as the reference bias for the PID controller, and the closed loop is responsible for correcting slow drift and model error.

8. The weak signal acquisition system based on frequency adaptive technology according to claim 7, characterized in that, The specific calculation methods for the inverse slope compensation function include: By obtaining Δθk,m and ΔAk,m on the discrete grid (ωk,Tm) through simulation or calibration, an inverse slope compensation is constructed: ； Data compression was achieved using bivariate polynomial regression: ； The coefficients aij were obtained through least squares fitting and written into the MCU.

9. The weak signal acquisition system based on frequency adaptive technology according to claim 8, characterized in that, The coefficients aij are obtained through least squares fitting, specifically including: Calculate or measure the gain difference ΔAk,m and phase difference Δθk,m at the grid points using electromagnetic simulation software; Construct a polynomial model with frequency order M and temperature order N. Each data point corresponds to an equation. Write the equations for all grid points in matrix form: Y = Xa, where Y is a column vector consisting of all ΔA or Δθ observations, and X is the design matrix with each row in [1, ω, T, ω 2 ,ωT,T 2 ,…],a:The coefficient vector aij to be fitted, and the least squares solution is obtained.

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