Liquid viscosity measuring method based on phase-locked loop algorithm

Abstract

The invention discloses a liquid viscosity measuring method based on a phase-locked loop algorithm. Liquid flows in the guided wave resonance element, the excitation and receiving coil is arranged on the surface of the guided wave resonance element in an attached mode, a permanent magnet is arranged beside the excitation and receiving coil, the temperature control module is connected with the guided wave resonance element, and the current sampling resistor is connected with the excitation and receiving coil in series. Ultrasonic guided-wave vibration is generated in a guided-wave resonant element through an exciting coil, voltage and current response signals of the resonant element are synchronously acquired by using a dual-channel synchronous sampling module, an impedance real part of the resonant element is accurately extracted according to the response signals, and accurate measurement of the liquid viscosity is realized by combining an established impedance-viscosity relation model. According to the invention, not only are the limitations of complex equipment, high cost and high requirement on sample volume of the traditional viscosity measurement method overcome, but also the problems of poor measurement stability, complex device manufacturing and difficulty in realizing online real-time monitoring under the working condition of strong noise or high damping in the existing method are solved.

Description

Technical Field

[0001] This invention belongs to the field of liquid viscosity measurement technology, specifically involving a liquid viscosity measurement method based on a phase-locked loop algorithm. Background Technology

[0002] In industrial production, biomedicine, and environmental monitoring, the viscosity of liquids is a key physical property parameter, and its accurate measurement is crucial for ensuring process efficiency, product quality, and operational safety. Currently widely used viscosity measurement techniques (such as the rotation method and falling ball method) generally suffer from high sample consumption, typically requiring milliliter-level samples. Although some emerging micro-quantity detection solutions (such as optical sensing technologies) reduce sample requirements to some extent, their complex system structures and poor environmental interference resistance make them unsuitable for demanding applications such as on-site diagnostics and industrial online monitoring, which require both portability and environmental adaptability.

[0003] The propagation of ultrasonic guided waves in slender elastic bodies is extremely sensitive to interfacial viscous dissipation. Their resonant frequency, propagation velocity, and attenuation characteristics change significantly with variations in liquid viscosity. Therefore, ultrasonic guided waves offer significant advantages in micro-liquid detection, rapid response, and integrable measurement scenarios, including high sensitivity, small sample requirements, and ease of online monitoring. Nevertheless, most existing viscosity measurements based on ultrasonic guided waves still rely on traditional impedance analysis techniques. These techniques typically use broadband excitation and high-performance impedance analyzers to obtain the resonant frequency of the guided wave resonant element through frequency domain sweeping or FFT of the freely decaying signal. However, frequency domain sweeping has a long measurement cycle, making real-time monitoring difficult and resulting in complex and expensive hardware. Time-domain FFT requires a long sampling window to ensure frequency resolution, is time-consuming, and is sensitive to noise, easily leading to spectral distortion. Furthermore, both methods require reconstructing a broadband frequency response, placing high demands on the bandwidth of the front-end circuitry, making it difficult to reduce system size and power consumption. Especially in high-viscosity liquids, the resonance peak becomes indistinct or the effective duration of the attenuation signal is insufficient due to the rapid decay of guided wave energy. Traditional methods are difficult to obtain stable and reliable viscosity measurement results in high-damping environments. Summary of the Invention

[0004] This invention aims to solve the problems of long measurement cycles, sensitivity to noise, complex hardware structure, and poor stability in high-damped liquids in traditional ultrasonic guided wave viscosity measurements. By introducing a phase-locked loop (PLL) method, this invention can quickly and accurately extract the resonance characteristics of guided wave resonant elements without relying on complex broadband measurement hardware and strict anti-interference environmental conditions. This enables highly sensitive measurement of liquid viscosity and provides the system with low cost, miniaturization, and real-time online monitoring capabilities.

[0005] This invention is achieved through the following technical solution: 1) Control the operation of the system, acquire the voltage and current signals of the excitation and receiving coils, extract the real part of the impedance, and establish a response curve based on the real part of the impedance to obtain the resonant frequency of the waveguide resonant element. 2) Under air or no-load conditions, measure the resonance frequency of the waveguide resonator in step 1) above, and use it as the no-load resonance frequency f0. The air or no-load environment refers to a system where no liquid flows inside the guide wave resonator element, or where air flows.

[0006] 3) Then, inject a calibration liquid with a known density ρ and viscosity η into the inner cavity of the waveguide resonator element. Specifically, inject it into the waveguide resonator element 1 or its encapsulation cavity using a micro-syringe. Repeat step 1) above, and measure the calibration resonant frequency f under the load condition of the injected calibration liquid. s ; 4) For the liquid to be tested, based on the no-load resonant frequency f0 and the calibration resonant frequency f s A viscosity measurement model is established to obtain the viscosity of the liquid to be tested.

[0007] In step 1), under operating conditions, the temperature control module and the control module form a closed-loop temperature control to maintain the measurement environment at a set constant temperature condition. The set constant temperature condition is usually 25 degrees Celsius.

[0008] Step 1) specifically refers to: 11) The signal excitation module outputs a sinusoidal excitation signal of specified frequency and amplitude to the excitation and receiving coils according to the preset frequency sweep method, which drives the waveguide resonant element to generate forced vibration; the dual-channel synchronous sampling module synchronously and directly acquires the voltage signal U in the excitation circuit of the excitation and receiving coils, and acquires the voltage signal across the current sampling resistor to obtain the current signal I of the excitation and receiving coils. Specifically, the current signal I of the excitation and receiving coils is obtained by dividing the voltage signal across the current sampling resistor by the current sampling resistor, and the acquired data is sent to the control module. 12) The control module transmits the voltage and current signals acquired by the dual-channel synchronous sampling module to the data processing module. The data processing module uses the phase-locked loop algorithm to extract the phase difference θ between the voltage and the current, and calculates the real part of the impedance based on the phase difference θ. 13) In the equivalent lumped parameter model of the sensor system, the mechanical vibration of the waveguide resonant element 1 is equivalent to an RLC resonant circuit, and its real part of impedance reaches a maximum value at the mechanical resonance. This maximum value can be obtained by scanning the excitation frequency.

[0009] By repeatedly scanning the excitation frequency using steps 3) and 4), a response curve showing the real part of the impedance changing with the excitation frequency is obtained. The horizontal axis of the curve represents the excitation frequency, and the vertical axis represents the real part of the impedance. After the frequency sweep is completed, the data processing module automatically tracks the maximum point of the response curve and uses the maximum point as the resonance peak. The excitation frequency at the maximum point is determined as the resonance frequency of the waveguide resonant element. At the same time, the impedance response curve and the marked resonance peak are displayed in real time on the display module.

[0010] Step 12) specifically involves: 121) The control module 8 transmits the voltage signal u(t) and current signal i(t) acquired by the dual-channel synchronous sampling module 5 to the data processing module 9. In the data processing module 9, the voltage signal u(t) and current signal i(t) acquired by the dual-channel synchronous sampling module are processed using a phase-locked loop algorithm to obtain the instantaneous phase. 1211) Input signal U in The following transfer function is used to construct a set of orthogonal signal components α and β in the input phase-locked loop: α(s) = U in (s)*kωs / (s 2 +kωs+ω 2 ) β(s) = U in (s)*kω 2 / (s 2 +kωs+ω 2 ) Where α represents the signal component with the same frequency and phase as the input signal, β represents the signal component that lags the input signal by 90°; s represents the Laplace transform operator, used to characterize the complex frequency variable in the complex frequency domain, ω represents the center angular frequency of the system, and U in α(s) represents the Laplace transform of the input signal in the complex frequency domain, α(s) represents the in-phase component of the output signal, and β(s) represents the quadrature component of the output signal. This step, by adjusting the gain coefficient k, ensures that the sensor response signal achieves a high-precision orthogonal transformation while filtering out signal noise.

[0011] 1212) Based on the orthogonal signal components α and β, and combined with the phase estimation value θ obtained from the feedback in step 1213), out The signal components α and β of the AC component are converted into the DC component v in the synchronous rotating coordinate system using the Park transform according to the following formula. d and v q : ; Among them, v d and v qThese represent the DC components of the d-axis and q-axis in the synchronous rotating coordinate system after the Park transformation, respectively. d The component reflects the deviation between the currently estimated phase and the actual phase of the signal; 1213) The error signal v q The error frequency v is obtained after processing by the PI controller. f Then the error frequency v f With the preset center angular frequency ω c The summation yields the instantaneous angular frequency ω, and the integration of ω yields the estimated phase value θ. out , represented as: ω=ω c +(K p +K i / s)*v q θ out =∫ωdt Among them, K p K is the proportional gain, used to control the transient response speed of the system to frequency fluctuations; i 1 / s represents the integral gain, used to eliminate steady-state phase error during closed-loop tracking; 1 / s represents the integral element in the complex frequency domain, and t represents the continuous-time variable. The real-time phase estimate θ out As an instantaneous phase output, it is simultaneously fed back to the Park transform module for iterative feedback; By adjusting the output frequency ω through a linear combination of these two methods, the system can ensure real-time and accurate locking of the instantaneous phase of the guided wave resonator even in high-damped fluid environments. Closed-loop feedback adjustment forces the error signal v... q Approaching 0, thus enabling dynamic tracking of the frequency and phase of the input signal.

[0012] 122) Repeat the above steps to process the input voltage signal u(t) and current signal i(t) in the same way to obtain their respective instantaneous phase θ. U and θ I Then calculate the absolute phase difference θ = |θ U -θ I |; 123) Taking into account the phase difference, the real part of the impedance is calculated according to the following formula: R=U*cosθ / I Where U represents the maximum voltage in the voltage signal u(t), I represents the maximum current in the current signal i(t), R represents the real part of the impedance, and θ represents the phase difference.

[0013] Step 4) specifically involves: 41) First, determine the resonant frequency f under the load conditions of the injected calibration liquid. s The dimensional material parameter k is calculated using the following formula: k=(f s -f0) / ((ηρ) 1 / 2 ) Where η represents the viscosity of the calibration liquid, ρ represents the density of the calibration liquid, and k is a constant that depends on the size and material parameters of the waveguide resonator.

[0014] The dimensional material parameter k is stored in the storage module 10 for subsequent viscosity inversion calculations.

[0015] 42) Then, for the liquid to be tested, repeat step 1) above to obtain the resonant frequency f of the liquid to be tested. Ls As the load frequency f Ls Then, the resonant frequency f is calculated using the viscosity measurement model according to the following formula. Ls : η L =((f Ls -f0) / k) 2 / ρ L Where, ρ L The density of the liquid to be tested is measured in advance by an instrument. The viscosity of the liquid to be tested can be obtained from the formula.

[0016] Before step 1), the following steps are set: based on the structural geometric parameters and material mechanical properties of the waveguide resonator, its resonant frequencies are calculated. Then, based on the resonant frequencies, the operating frequency range, excitation amplitude, and sampling parameters of the waveguide resonator, signal excitation module, and dual-channel synchronous sampling module are determined. Specifically, the operating frequency range of the waveguide resonator, the excitation amplitude of the signal excitation module, and the sampling parameters of the dual-channel synchronous sampling module are determined as follows: In step 1), the control module controls the signal excitation module and the dual-channel synchronous sampling module to scan the excitation frequency according to the operating frequency range of the waveguide resonant element; In step 1), the control module sends an excitation command to the signal excitation module according to the excitation amplitude of the signal excitation module to make the excitation and receiving coils work; In step 1), the control module sends a control command to the dual-channel synchronous sampling module according to the sampling parameters of the dual-channel synchronous sampling module, so that the dual-channel synchronous sampling module receives the signal according to the sampling parameters.

[0017] The method employs a liquid viscosity measurement system, which includes a waveguide resonant element, excitation and receiving coils, a permanent magnet, a signal excitation module, a dual-channel synchronous sampling module, a current sampling resistor, and a temperature control module. Liquid flows inside the waveguide resonant element, the excitation and receiving coils are attached to the surface of the waveguide resonant element, a permanent magnet is placed beside the excitation and receiving coils, and the temperature control module is connected to the waveguide resonant element to detect and control the temperature of the waveguide resonant element. The current sampling resistor and the excitation and receiving coil are connected in series. The signal excitation module and the dual-channel synchronous sampling module are electrically connected to the excitation and receiving coils, respectively. At the same time, the dual-channel synchronous sampling module and the current sampling resistor are electrically connected, which are used to send signals to the excitation and receiving coils and receive signals from the excitation and receiving coils, respectively.

[0018] The waveguide resonant element is a plate-like structure, a tubular structure, or other slender elastic body capable of supporting the propagation of ultrasonic guided waves. Preferably, the waveguide resonant element adopts a pipe structure, in which liquid flows.

[0019] The excitation and receiving coils are wound around the outside of the waveguide resonant element, and the coil structure in the excitation and receiving coils is a planar coil or a solenoid coil.

[0020] The signal excitation module includes a pulse width modulator and a power amplifier, which are used to generate a stable pulse width modulated signal and drive the excitation and receiving coils after power amplification.

[0021] It also includes the aforementioned control module, data processing module, storage module, and display module. The signal excitation module, dual-channel synchronous sampling module, and temperature control module are all communicatively connected to the control module, and the data processing module, storage module, and display module are all communicatively connected to the control module.

[0022] This invention generates ultrasonic guided wave vibration in a waveguide resonant element by excitation coil, and uses a dual-channel synchronous sampling module to synchronously acquire the voltage and current response signals of the resonant element; based on the response signals, the real part of the impedance of the resonant element is accurately extracted, and combined with the established impedance-viscosity relationship model, the accurate measurement of liquid viscosity is achieved.

[0023] The beneficial effects of this invention are: This invention not only overcomes the limitations of traditional viscosity measurement methods, such as complex equipment, high cost, and large sample volume requirements, but also solves the problems of poor measurement stability under strong noise or high damping conditions, complex device manufacturing, and difficulty in achieving online real-time monitoring. Attached Figure Description

[0024] Figure 1 : Schematic diagram of the system structure of this invention; Figure 2 : A schematic diagram of a phase-locked loop algorithm based on second-order generalized integrals; Figure 3 Figure 1 shows the impedance measurement results under no-load and load conditions, where (a) represents the impedance measurement results under no-load conditions and (b) represents the impedance measurement results under load conditions.

[0025] In the diagram: 1. Waveguide resonant element; 2. Excitation and receiving coil; 3. Permanent magnet; 4. Signal excitation module; 5. Dual-channel synchronous sampling module; 6. Current sampling resistor; 7. Temperature control module; 8. Control module; 9. Data processing module; 10. Storage module; 11. Display module. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, the system includes a waveguide resonant element 1, an excitation and receiving coil 2, a permanent magnet 3, a signal excitation module 4, a dual-channel synchronous sampling module 5, a current sampling resistor 6, and a temperature control module 7. A waveguide resonant element 1 is fixedly positioned, and liquid flows inside the waveguide resonant element 1. An excitation and receiving coil 2 is attached to the surface of the waveguide resonant element 1, and a permanent magnet 3 is arranged beside the excitation and receiving coil 2. Temperature control module 7 is connected to waveguide resonant element 1 and is used to detect and control the temperature of waveguide resonant element 1, collect the temperature of waveguide resonant element 1 and control its temperature to keep it constant. The current sampling resistor 6 is connected in series with the excitation and receiving coil 2. The signal excitation module 4 and the dual-channel synchronous sampling module 5 are electrically connected to the excitation and receiving coil 2 respectively. At the same time, the dual-channel synchronous sampling module 5 is electrically connected to the current sampling resistor 6, which are used to send signals to the excitation and receiving coil 2 and receive signals from the excitation and receiving coil 2 respectively.

[0028] The waveguide resonant element 1 is a plate-shaped structure, a tubular structure, or other slender elastic body that can support the propagation of ultrasonic guided waves. The waveguide resonant element 1 is made of magnetostrictive material, which can be metal, alloy, or composite material with good elasticity and wave guiding properties.

[0029] Preferably, the waveguide resonant element 1 adopts a pipe structure, in which a liquid flows. The liquid is a Newtonian fluid.

[0030] The excitation and receiving coils 2 are wound around the waveguide resonator 1. The coil structure in the excitation and receiving coils 2 is a planar coil or a solenoid coil, or it can be designed as a bent or attached coil according to the geometry of the waveguide resonator 1.

[0031] The signal excitation module 4 includes a pulse width modulator and a power amplifier, which are used to generate a stable pulse width modulated signal and drive the excitation and receiving coils 2 after power amplification.

[0032] The signal excitation module 4 includes a signal generator and a power amplifier, which are used to generate a stable sinusoidal excitation signal with adjustable frequency and amplitude. After power amplification, the signal drives the excitation and receiving coils 2, so that the guided wave resonant element 1 generates controlled ultrasonic guided wave resonant vibration in the liquid.

[0033] It also includes a control module 8, a data processing module 9, a storage module 10, and a display module 11. The signal excitation module 4, the dual-channel synchronous sampling module 5, and the temperature control module 7 are all connected to the control module 8. The data processing module 9, the storage module 10, and the display module 11 are all connected to the control module 8.

[0034] The permanent magnet 3 is used to provide a bias magnetic field for the waveguide resonant element 1, and the current sampling resistor 6 is connected in series in the coil excitation circuit.

[0035] The signal excitation module 4, the dual-channel synchronous sampling module 5, and the temperature control module 7 are all electrically connected to the control module 8 to realize the excitation, response acquisition, and temperature regulation of the guided wave resonant element 1.

[0036] The display module 11 is used to display the relevant parameters acquired and measured in real time. Specifically, it can display the resonance frequency of the waveguide resonant element 1 and the calculated viscosity value of the liquid being measured in real time.

[0037] The storage module 10 is used to store the resonance frequency data of different liquids and their viscosity measurement results; The data processing module 9 is used to filter, extract features, calculate resonant frequency, and determine liquid viscosity based on the impedance-viscosity relationship model of the collected voltage and current signals.

[0038] In this invention, for the same waveguide resonant element, the higher the liquid viscosity, the faster the waveguide vibration it excites decays, the more obvious the energy dissipation, the more significant the change in impedance spectrum, and the greater the resonant frequency shift.

[0039] The principle of the liquid viscosity measurement method based on the phase-locked loop algorithm of the present invention is as follows: When a frequency-tunable narrowband excitation signal is applied to the waveguide resonator, the dual-channel synchronous sampling module acquires the excitation voltage and response current signals respectively. A stable fundamental component is extracted from the original signal, and the phase difference between the voltage and current is calculated in real time in combination with a phase-locked loop algorithm.

[0040] Then, the fundamental component is extracted from the input voltage and current signals, and the instantaneous phase is estimated in real time. By utilizing the fast phase-locked loop (PLL) algorithm and robust filtering capabilities, the speed and noise immunity of impedance spectrum reconstruction are improved, thus enabling stable acquisition of resonance characteristics even under high-damped liquid conditions. The offset of the resonance frequency has a definite relationship with the liquid viscosity; by comparing the resonance frequencies under no-load and liquid-loaded conditions, the viscosity of the measured liquid can be calculated.

[0041] In this embodiment, the waveguide resonant element uses a tubular elastic body with a length of 100 mm, an outer diameter of 1.5 mm, and an inner diameter of 1.0 mm as the resonant structure. The excitation and receiving coils are solenoid-type structures, coaxially sleeved outside the resonant element, with 200 turns and a wire diameter of 0.25 mm. The permanent magnet used to provide the bias magnetic field is a square magnet magnetized in the thickness direction, with dimensions of 10 mm × 5 mm × 3 mm. The temperature control module consists of a platinum resistance temperature sensor and a semiconductor thermoelectric cooler, used to monitor and adjust the operating temperature of the resonant element.

[0042] The liquid viscosity measurement process and examples of this invention are as follows: 1) Calculate the natural resonant frequencies of waveguide resonant element 1 according to its geometric parameters and the mechanical properties of the material; and set the operating frequency range, excitation amplitude and sampling rate of excitation and receiving coil 2, signal excitation module 4 and dual-channel synchronous sampling module 5 according to the determined target resonant frequency range.

[0043] In this embodiment, a sinusoidal signal with a sweep frequency range of 0 to 200 kHz and a peak value of 12 V is selected based on the inner and outer diameters, material density, Poisson's ratio, and elastic modulus of the selected tubular waveguide resonant element. The sampling frequency is chosen to be 5 MHz.

[0044] 2) Temperature control module 7 and control module 8 form a closed-loop temperature regulation circuit. Temperature control module 7 measures the temperature of the waveguide resonant element in real time through temperature sensor and controls the semiconductor heating and cooling chip to keep the measurement environment at the set constant temperature condition of 25°C. At the same time, it checks and ensures that the waveguide resonant element 1 is in a dry and clean state.

[0045] 3) The signal excitation module 4 outputs a sinusoidal excitation signal of specified frequency and amplitude to the excitation and receiving coil 2 in a frequency sweep mode from 0 to 200kHz, so that the waveguide resonant element 1 generates forced vibration; the dual-channel synchronous sampling module 5 synchronously collects the voltage U in the excitation circuit and the voltage across the current sampling resistor, thereby obtaining the corresponding current I, and sends the collected data to the control module 8.

[0046] 4) Control module 8 transmits the voltage and current signals acquired by dual-channel synchronous sampling module 5 to data processing module 9. For example... Figure 2As shown, the data processing module 9 uses a phase-locked loop algorithm to extract the phase difference θ between voltage and current, and calculates the real part of the impedance accordingly.

[0047] 5) In the equivalent lumped parameter model of the sensor system, the mechanical vibration of the waveguide resonant element 1 can be equivalent to an RLC resonant circuit, whose real part of impedance reaches its maximum at mechanical resonance. Therefore, by scanning the excitation frequency and calculating the corresponding real part of impedance R, the impedance response curve as a function of frequency can be obtained. After the frequency sweep is completed, the data processing module 9 automatically tracks the maximum point of the curve and determines it as the resonant frequency of the waveguide resonant element 1; at the same time, the impedance response curve and the marked resonant peak value are displayed in real time on the display module 11, such as... Figure 3 As shown.

[0048] 6) For example Figure 3 As shown in (a), the resonant frequency of the waveguide resonant element 1 is measured in air or in an unloaded environment. This frequency is denoted as the unloaded resonant frequency f0. In this embodiment, the unloaded resonant frequency f0 is 130.8 kHz.

[0049] 7) Inject the calibration liquid with a pre-measured density of ρ and viscosity of η into the waveguide resonator 1 or its encapsulation cavity using a micro-syringe, and repeat steps 2) to 5). Record the calibration resonant frequency f under liquid load conditions. s It is 126.4kHz, such as Figure 3 As shown in (b).

[0050] 8) According to the calibrated resonant frequency f s The parameter k is calculated and calibrated experimentally. The value of k is then stored in storage module 10 for subsequent viscosity inversion calculations.

[0051] 9) For the sample to be tested, its density is measured by the instrument and recorded as ρ. L Repeat steps 2) to 5) to obtain the load frequency f of the sample to be tested. Ls Then, the viscosity η of the liquid to be tested is obtained according to the formula. L .

[0052] With further improvements in sweep frequency resolution, the accuracy of resonant frequency identification and viscosity calculation results can still be improved accordingly.

[0053] Comparative Example 1: Comparative Example 1 provides a liquid viscosity measurement method based on a guided wave resonator. The guided wave resonator, excitation and receiving coils, permanent magnet, signal excitation module, dual-channel synchronous sampling module, temperature control module, and test sample are all identical to those in this embodiment. The difference lies in that Comparative Example 1 uses a traditional analog phase-locked loop circuit to track the phase relationship and extract the frequency between the excitation and response signals, instead of employing the phase-locked loop algorithm of this invention.

[0054] In Comparative Example 1, the excitation signal and the received signal are compared in phase and filtered by an analog phase-locked loop circuit. The output of the voltage-controlled oscillator follows the resonant frequency change of the waveguide resonant element, thereby achieving the measurement of the resonant frequency. The loop parameters of this phase-locked loop circuit are set during the design phase and remain fixed during the measurement process.

[0055] Using the same waveguide resonant element and calibration liquid as in this embodiment, tests were conducted at a constant temperature of 25 degrees Celsius. Experimental results show that when the liquid viscosity is low and the waveguide damping is weak, Comparative Example 1 can achieve resonant frequency locking; however, as the liquid viscosity increases, the response signal amplitude decreases and the phase noise increases, significantly reducing the locking speed and stability of the traditional analog phase-locked loop. This easily leads to limited locking range or unstable tracking, resulting in increased resonant frequency measurement error and consequently affecting the accuracy of liquid viscosity measurement.

[0056] In contrast, this invention introduces a phase-locked loop algorithm into the data processing module, which reduces hardware complexity while flexibly adjusting the loop bandwidth and locking parameters, and effectively suppresses noise. As a result, it can still stably extract the resonant frequency of the waveguide resonator under strongly damped liquid conditions, which greatly improves the stability and reliability of liquid viscosity measurement.

[0057] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0058] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A liquid viscosity measurement method based on a phase-locked loop algorithm, characterized in that, The method includes the following steps: 1) The control system works, acquires the voltage and current signals of the excitation and receiving coils (2), and then extracts the real part of the impedance. Based on the real part of the impedance, a response curve is established to obtain the resonance frequency of the waveguide resonant element (1). 2) Under air or no-load conditions, measure the resonance frequency of the waveguide resonant element (1) according to the above step 1) and use it as the no-load resonance frequency f0. 3) Then, inject a calibration liquid with a known density ρ and viscosity η into the inner cavity of the waveguide resonant element (1), and repeat step 1) above to measure the calibration resonant frequency f under the load condition of the injected calibration liquid. s ; 4) For the liquid to be tested, based on the no-load resonant frequency f0 and the calibration resonant frequency f s A viscosity measurement model is established to obtain the viscosity of the liquid to be tested.

2. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 1, characterized in that, In step 1), under working conditions, the temperature control module (7) and the control module (8) form a closed-loop temperature control to keep the measurement environment at the set constant temperature conditions.

3. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 1, characterized in that, Step 1) specifically refers to: 11) The signal excitation module (4) outputs a sinusoidal excitation signal with a specified frequency and amplitude to the excitation and receiving coil (2) according to the preset frequency sweep method, which drives the waveguide resonant element (1) to generate forced vibration; the dual-channel synchronous sampling module (5) synchronously collects the voltage signal U of the excitation and receiving coil (2), and collects the voltage signal across the current sampling resistor (6) to obtain the current signal I of the excitation and receiving coil (2), and sends the collected data to the control module (8); 12) The control module (8) transmits the voltage and current signals obtained by the dual-channel synchronous sampling module (5) to the data processing module (9). The data processing module (9) uses the phase-locked loop algorithm to extract the phase difference θ between the voltage and the current, and calculates the real part of the impedance based on the phase difference θ. 13) By repeatedly scanning the excitation frequency in steps 3) and 4), the response curve of the real part of the impedance changing with the excitation frequency is obtained. After the frequency sweep is completed, the data processing module (9) automatically tracks the maximum point of the response curve and determines the excitation frequency at the maximum point as the resonance frequency of the waveguide resonant element (1).

4. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 3, characterized in that, Step 12) specifically involves: 121) In the data processing module (9), the voltage signal u(t) and current signal i(t) collected by the dual-channel synchronous sampling module (5) are respectively processed by the phase-locked loop algorithm to obtain the instantaneous phase; 1211) Input signal U in The following transfer function is used to construct a set of orthogonal signal components α and β in the input phase-locked loop: α(s)= U in (s)*kωs / (s 2 +kωs+ω 2 ) β(s)= U in (s)*kω 2 / (s 2 +kωs+ω 2 ) Where α represents the signal component with the same frequency and phase as the input signal, β represents the signal component that lags the input signal by 90°; s represents the Laplace transform operator, used to characterize the complex frequency variable in the complex frequency domain, ω represents the center angular frequency of the system, and U in α(s) represents the Laplace transform of the input signal in the complex frequency domain, α(s) represents the in-phase component of the output signal, and β(s) represents the quadrature component of the output signal. 1212) Based on the orthogonal signal components α and β, and combined with the phase estimation value θ obtained from the feedback in step 1213), out The signal components α and β are converted into DC components v in a synchronous rotating coordinate system using the Park transform according to the following formula. d and v q : ； Among them, v d and v q These represent the DC components of the d-axis and q-axis in the synchronous rotating coordinate system after the Park transformation; 1213) The error signal v q The error frequency v is obtained after processing by the PI controller. f Then the error frequency v f With the preset center angular frequency ω c The summation yields the instantaneous angular frequency ω, and the integration of ω yields the estimated phase value θ. out , is represented as: ω=ω c +(K p +K i / s*v q i out =∫ωdt Among them, K p For proportional gain; K i is the integral gain; 1 / s represents the integral element in the complex frequency domain, and t represents the continuous-time variable; The phase estimate θ obtained in real time out As an instantaneous phase output, it is simultaneously fed back to the Park transform for iterative feedback; 122) Repeat the above steps to process the input voltage signal u(t) and current signal i(t) in the same way to obtain their respective instantaneous phase θ. U and θ I Then calculate the absolute phase difference θ = |θ U -θ I |; 123) Taking into account the phase difference, the real part of the impedance is calculated according to the following formula: R=U*cosθ / I Where U represents the maximum voltage in the voltage signal u(t), I represents the maximum current in the current signal i(t), R represents the real part of the impedance, and θ represents the phase difference.

5. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 1, characterized in that, Step 4) specifically involves: 41) First, determine the resonant frequency f under the load conditions of the injected calibration liquid. s The dimensional material parameter k is calculated using the following formula: k=(f s -f0) / ((ir) 1 / 2 ) Where η represents the viscosity of the calibration liquid, and ρ represents the density of the calibration liquid; 42) Then, for the liquid to be tested, repeat step 1) above to obtain the resonant frequency f of the liquid to be tested. Ls Then, the resonant frequency f is calculated using the viscosity measurement model according to the following formula. Ls : η L =((f Ls -f0) / k) 2 / ρ L Where, ρ L This indicates the density of the liquid being tested.

6. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 1, characterized in that, Before step 1), it is also set that, based on the structural geometric parameters and material mechanical properties of the waveguide resonant element (1), its resonant frequencies of each order are calculated, and then the operating frequency range, excitation amplitude and sampling parameters of the waveguide resonant element (1), signal excitation module (4) and dual-channel synchronous sampling module (5) are determined according to the resonant frequencies.

7. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 1, characterized in that, The method employs a liquid viscosity measurement system, which includes a waveguide resonant element (1), an excitation and receiving coil (2), a permanent magnet (3), a signal excitation module (4), a dual-channel synchronous sampling module (5), a current sampling resistor (6), and a temperature control module (7). Liquid flows inside the waveguide resonant element (1), the excitation and receiving coil (2) is attached to the surface of the waveguide resonant element (1), and a permanent magnet (3) is provided on the side of the excitation and receiving coil (2). The temperature control module (7) is connected to the waveguide resonant element (1) and is used to detect and control the temperature of the waveguide resonant element (1). The current sampling resistor (6) and the excitation and receiving coil (2) are connected in series. The signal excitation module (4) and the dual-channel synchronous sampling module (5) are electrically connected to the excitation and receiving coil (2) respectively. At the same time, the dual-channel synchronous sampling module (5) and the current sampling resistor (6) are electrically connected, which are used to send signals to the excitation and receiving coil (2) and receive signals from the excitation and receiving coil (2) respectively.

8. The liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 7, characterized in that, The waveguide resonant element (1) is a plate-shaped structure, a tubular structure, or other slender elastic body that can support the propagation of ultrasonic waveguides.

9. A liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 7, characterized in that, The excitation and receiving coil (2) is wound around the outside of the waveguide resonant element (1), and the coil structure in the excitation and receiving coil (2) is a planar coil or a solenoid coil.

10. A liquid viscosity measurement method based on a phase-locked loop algorithm according to claim 7, characterized in that, It also includes the control module (8), data processing module (9), storage module (10) and display module (11). The signal excitation module (4), dual-channel synchronous sampling module (5) and temperature control module (7) are all connected to the control module (8) in communication. The data processing module (9), storage module (10) and display module (11) are all connected to the control module (8) in communication.

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