CN-121977669-A - Dynamic liquid level detection system and method based on stirred tank

CN121977669ACN 121977669 ACN121977669 ACN 121977669ACN-121977669-A

Abstract

The invention discloses a dynamic liquid level detection system and method based on a stirred tank, and belongs to the field of liquid level detection. The system comprises a differential pressure sensor module, a rotating speed acquisition module and a signal processing unit, wherein the signal processing unit comprises a vortex dynamic compensation module, a self-adaptive filtering module and a delay prediction compensation module which are sequentially connected in series. The invention collects the differential pressure signal of the liquid column in the kettle and converts the differential pressure signal into an apparent liquid level value, simultaneously collects the rotating speed signal of the stirring paddle, calculates the liquid level offset at the kettle wall caused by vortex according to the rotating speed signal, tracks and outputs dynamic compensation quantity through first-order recursion to eliminate the vortex liquid level offset, adaptively determines the cut-off frequency of a low-pass filter according to the rotating speed signal to inhibit stirring fluctuation noise, and carries out forward prediction correction by utilizing the change rate and group delay of the filtered liquid level value to reduce filtering delay. According to the invention, the rotation speed signal is used as a tie to realize dynamic coordination of all links, so that the accuracy and response speed of liquid level measurement under stirring working conditions are improved.

Inventors

JI GUANGXING
ZHANG LAIQING
WANG LI
NI XIAOWEI
HU QIMIN

Assignees

山东凯恩新材料科技有限公司

Dates

Publication Date: 20260505
Application Date: 20260408

Claims (7)

1. The dynamic liquid level detection method based on the stirred tank is characterized by comprising the following steps of: S1, differential pressure liquid level acquisition, namely acquiring a differential pressure signal of a liquid column in a stirring kettle through a differential pressure sensor arranged on the stirring kettle, and converting the differential pressure signal into an apparent liquid level value; S2, acquiring a rotating speed signal of the stirring paddle in real time through a rotating speed sensor arranged at the driving end of the stirring paddle; S3, vortex sinking dynamic compensation, namely calculating a liquid level steady-state offset at the kettle wall caused by stirring vortex according to the rotating speed signal to serve as a steady-state compensation target value, gradually approaching the dynamic compensation quantity to the steady-state compensation target value cycle by cycle through a first-order recursive tracking link, and subtracting the dynamic compensation quantity from the apparent liquid level value at the current sampling moment to obtain a compensated liquid level value; S4, self-adaptive filtering, namely determining the cut-off frequency of a low-pass filter according to the rotating speed signal, enabling the cut-off frequency to be self-adaptively adjusted along with the stirring rotating speed, and carrying out filtering treatment on the compensated liquid level value to obtain a filtered liquid level value; S5, filtering delay prediction compensation, namely calculating the group delay of the low-pass filter according to the cut-off frequency, and performing forward prediction correction by utilizing the change rate of the filtered liquid level value and the group delay to obtain a final liquid level measured value.
2. The method according to claim 1, characterized in that said step S1 comprises the sub-steps of: S11, respectively arranging pressure transmitters at a bottom pressure measuring point and a top pressure measuring point of the stirring kettle, and collecting differential pressure values between the bottom pressure measuring point and the top pressure measuring point The substep obtains a liquid column differential pressure signal which eliminates the influence of gas phase pressure in the kettle; S12, according to the differential pressure value And the density of the materials in the kettle, and calculating the apparent liquid level value according to the following formula: ; Wherein, the Is the apparent liquid level value; is the differential pressure value; The density of the materials in the kettle; Gravitational acceleration; and obtaining the apparent liquid level value corresponding to the liquid column height at the kettle wall.
3. The method according to claim 1, characterized in that said step S3 comprises the sub-steps of: s31, acquiring the current rotation speed of the stirring paddle according to the rotation speed signal The paddle angular velocity is calculated as follows: ; Wherein, the Is the angular speed of the stirring paddle; 60 is the conversion coefficient of minutes and seconds; converting the rotational speed signal into an angular speed; S32, according to the angular velocity of the stirring paddle And the inner radius of the stirring kettle The steady state compensation target value is calculated as follows: ; Wherein, the Compensating the target value for the steady state; The eddy compensation coefficient is determined by calibration; -the paddle angular velocity; the inner radius of the stirring kettle is set; Gravitational acceleration; Calculating the steady-state offset of the liquid level at the kettle wall corresponding to the current rotating speed; s33, updating the dynamic compensation quantity in each sampling period through the following first-order recursive formula to enable the dynamic compensation quantity to gradually approach the steady-state compensation target value: ; Wherein, the Is the first The dynamic compensation amounts at the sampling moments; Is the first The dynamic compensation amounts at the sampling moments; Is the first The steady-state compensation target value calculated by step S32 at each sampling time; is a tracking coefficient The calculation formula of (2) is as follows: ; Wherein, the Is the sampling period; Is a vortex response time constant, and is determined by calibration; S34, subtracting the dynamic compensation amount from the apparent liquid level value at the current sampling moment according to the following formula to obtain the compensated liquid level value: ; Wherein, the For the compensated liquid level value; is the apparent liquid level value; Is the first The amount of dynamic compensation at each sampling instant.
4. The method according to claim 1, characterized in that said step S4 comprises the sub-steps of: S41, acquiring the current rotation speed of the stirring paddle according to the rotation speed signal The paddle rotation frequency is calculated and the cut-off frequency of the low pass filter is determined as follows: ; Wherein, the The rotation frequency of the stirring paddle; 60 is the conversion coefficient of minutes and seconds; ; Wherein, the Is the cut-off frequency; is a frequency scaling factor; the cut-off frequency is set to be the rotation frequency of the stirring paddle when the rotation speed of the stirring paddle is lower than a rotation speed threshold value determined by the characteristic of stirring fluctuation noise Taking a preset fixed value; s42, at the cut-off frequency Constructing a second-order Butterworth low-pass filter, discretizing the second-order Butterworth low-pass filter into a differential equation through bilinear transformation, filtering the compensated liquid level value to obtain a filtered liquid level value, and when the cut-off frequency is high When the change occurs, the filter coefficient is recalculated and the new and old coefficients are weighted and smoothly transited; stirring fluctuation noise can be restrained at different rotating speeds, and real liquid level change information is reserved.
5. The method according to claim 4, wherein said step S5 comprises the sub-steps of: S51, according to the cut-off frequency The group delay of the low pass filter within the passband is calculated as: ; Wherein, the For the group delay; Is the cut-off frequency when The group delay varies with the rotation speed Synchronously updating; obtaining a response delay amount under the current filtering condition; s52, calculating the change rate by using the last plurality of sampling values of the filtered liquid level value according to the following formula: ; Wherein, the Is an estimated value of the change rate; Is the first The filtered liquid level values at the sampling moments; Is the first The filtered liquid level values at the sampling moments; Taking a positive integer for the number of differential interval points; is the sampling period; Obtaining the variation trend of the filtered liquid level value; S53, performing forward prediction correction on the filtered liquid level value according to the following formula to obtain the final liquid level measurement value: ; Wherein, the For the final level measurement; Is the first The filtered liquid level values at the sampling moments; For the group delay; estimating the rate of change when And (3) with When the absolute value of the product of (a) exceeds a preset maximum correction amount, taking the preset maximum correction amount as an actual correction amount, and taking the sign and the sign of the actual correction amount And the substep reduces the response delay introduced by the low-pass filter to obtain the final liquid level measurement value.
6. A stirred tank based dynamic liquid level detection system comprising: the differential pressure sensor module comprises two pressure transmitters respectively arranged at a bottom pressure measuring point and a top pressure measuring point of the stirring kettle, and is used for acquiring a differential pressure signal of a liquid column in the kettle and outputting an apparent liquid level value; The rotating speed acquisition module is arranged at the driving end of the stirring paddle and used for acquiring rotating speed signals of the stirring paddle in real time; The signal processing unit is respectively connected with the differential pressure sensor module and the rotating speed acquisition module in a signal way, and comprises a vortex dynamic compensation module, a self-adaptive filtering module and a delay prediction compensation module which are sequentially connected in series, wherein the vortex dynamic compensation module is used for calculating a steady-state offset of the liquid level at the kettle wall caused by stirring vortex according to the rotating speed signal and outputting the dynamic compensation quantity through a first-order recursive tracking link, compensating the apparent liquid level value and outputting a compensated liquid level value, the self-adaptive filtering module is used for determining a cut-off frequency according to the rotating speed signal and carrying out low-pass filtering on the compensated liquid level value and outputting a filtered liquid level value, and the delay prediction compensation module is used for calculating group delay according to the cut-off frequency and utilizing the change rate of the filtered liquid level value to carry out forward prediction correction and then outputting a final liquid level measured value.
7. The system of claim 6, wherein the input end of the vortex dynamic compensation module is respectively connected with the differential pressure sensor module and the rotation speed acquisition module, the output end of the vortex dynamic compensation module is connected with the adaptive filtering module, the adaptive filtering module is further connected with the rotation speed acquisition module and is used for receiving the rotation speed signal to determine a cut-off frequency, the output end of the adaptive filtering module is connected with the delay prediction compensation module, and the rotation speed signal is simultaneously used as input parameters of the vortex dynamic compensation module and the adaptive filtering module to form a dual-channel signal processing framework taking the rotation speed signal as a core.

Description

Dynamic liquid level detection system and method based on stirred tank Technical Field The invention relates to the technical field of liquid level detection, in particular to a dynamic liquid level detection system and method based on a stirring kettle. Background The stirring kettle is core equipment for realizing operations such as material mixing, dissolving, reaction and the like, and accurate measurement of liquid level in the kettle has important significance for safe operation and accurate control of a production process. The common differential pressure type liquid level measurement technology indirectly calculates the liquid level height by measuring the pressure difference between the bottom and the top of the liquid column. However, during operation of the stirred tank, the rotation of the stirring paddles creates forced vortices in the liquid in the tank, causing the liquid level near the tank wall to rise due to centrifugal forces, creating a vortex dishing effect. Because the pressure taking point of the differential pressure sensor is usually positioned at the kettle wall, the liquid level bulge at the kettle wall caused by stirring vortex can cause the measured value of the differential pressure type liquid level meter to systematically deviate from the real average liquid level in the kettle, and the deviation amount dynamically changes along with the change of the rotating speed of the stirring paddle, the traditional differential pressure liquid level detection scheme generally lacks the capability of carrying out real-time dynamic compensation on the stirring vortex effect, so that the liquid level measurement has obvious system errors under the stirring working condition. In addition, the periodic disturbance of the liquid surface by the stirring paddle during rotation can superimpose fluctuation noise in the liquid level signal, and the frequency characteristic of the noise is closely related to the rotating speed of the stirring paddle. The existing liquid level signal filtering processing scheme generally adopts a low-pass filter with fixed parameters, but the filter with fixed cutoff frequency is difficult to simultaneously consider the noise suppression effect and the signal response speed under the variable speed running condition of the stirring paddle, the problem of insufficient noise suppression caused by the fact that the cutoff frequency is higher than the stirring fluctuation frequency easily occurs under the low-rotation-speed working condition, and excessive signal delay can be introduced due to the fact that the cutoff frequency is lower than the stirring fluctuation frequency under the high-rotation-speed working condition. Meanwhile, the low-pass filter inevitably introduces response delay in the process of noise suppression, so that the filtered liquid level measured value generates time delay relative to the real liquid level, the delay can have adverse effect on the performance of the closed-loop liquid level control system under the feeding or discharging working condition of rapid change of the liquid level, and the prior scheme generally lacks measures for effectively compensating the filtering delay. Therefore, the design of the dynamic liquid level detection system and the method for solving the technical problems has important significance. Disclosure of Invention In order to solve the problems in the background technology, the invention provides a dynamic liquid level detection method based on a stirring kettle, which comprises the following steps: S1, differential pressure liquid level acquisition, namely acquiring a differential pressure signal of a liquid column in a stirring kettle through a differential pressure sensor arranged on the stirring kettle, and converting the differential pressure signal into an apparent liquid level value; S2, acquiring a rotating speed signal of the stirring paddle in real time through a rotating speed sensor arranged at the driving end of the stirring paddle; S3, vortex sinking dynamic compensation, namely calculating a liquid level steady-state offset at the kettle wall caused by stirring vortex according to the rotating speed signal to serve as a steady-state compensation target value, gradually approaching the dynamic compensation quantity to the steady-state compensation target value cycle by cycle through a first-order recursive tracking link, and subtracting the dynamic compensation quantity from the apparent liquid level value at the current sampling moment to obtain a compensated liquid level value; S4, self-adaptive filtering, namely determining the cut-off frequency of a low-pass filter according to the rotating speed signal, enabling the cut-off frequency to be self-adaptively adjusted along with the stirring rotating speed, and carrying out filtering treatment on the compensated liquid level value to obtain a filtered liquid level value; S5, filtering delay prediction compensation, namely calculating the group