Microwave type liquid concentration measuring device
Through the combination of two-channel RF transceiver modules and temperature sensors, combined with the digital signal processing of AD936x chip and FPGA, the problem of microwave concentration meter being affected by the environment and temperature is solved, achieving more stable and accurate concentration measurement.
Patent Information
- Application Number
- CN202420670626.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-02
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2034-04-02
AI Technical Summary
The existing microwave concentration meters are greatly affected by the environment and ambient temperature, have poor stability, and have large errors in phase difference calculation, resulting in unstable system during actual operation.
Using two-channel RF transceiver modules, a temperature sensor is added to compensate through the RF transceiver unit connected to the receiving antenna and the transmitting antenna, and digital signal processing is performed using AD936x chip and FPGA. The traditional circuit method of finding phase difference is discarded, and the frequency is increased by combining constant temperature crystal oscillator. stability.
It improves the stability of the system and the accuracy of phase difference, adapts to changes in large pipeline diameters, expands the measurement concentration range, and reduces the impact of the environment on the system.
Smart Images
Figure CN222212557U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of papermaking and chemical concentration detection, in particular to a microwave liquid concentration measuring device. Background Art
[0002] Densitometers are essential monitoring instruments for the production process monitoring of light industrial manufacturing such as papermaking, food, and chemicals. For example, in the papermaking industry, the commonly used instruments for measuring pulp concentration are moving knife densitometers, ultrasonic densitometers, and microwave densitometers. Moving knife densitometers use the shear force of the pulp in the pipeline on the rotating blade to measure the pulp concentration. Moving knife densitometers have a small measurement range and are greatly affected by the measured liquid and the flow rate. At the same time, due to mechanical wear, the accuracy and life of long-term operation are reduced. The ultrasonic densitometer probe is prone to scaling and is greatly affected by bubbles. It is inconvenient to clean in the pipeline, which greatly limits the use of densitometers. Microwave densitometers overcome the above shortcomings and have the advantages of high measurement accuracy, wide measurement range, and no influence from liquid flow rate.
[0003] The microwave concentration meter can measure the concentration of the liquid by detecting the propagation time of microwaves passing through a certain distance of liquid medium, and then calibrating it with a standard liquid (such as water, pulp of known concentration). Since it is difficult to directly measure the delay time, a sine wave is emitted on one side of the pipe wall, and then after receiving the echo at the opposite receiving end, the phase difference between the emitted wave and the echo is compared, and the delay time is calculated through the frequency. The propagation speed of microwaves in the liquid can be calculated through the delay time, the dielectric constant of the liquid can be calculated through the propagation speed, and the liquid concentration can be calibrated through the dielectric constant. In actual operation, there is a corresponding relationship between the phase difference and the liquid concentration: concentration = k(θ2-θ1)+B (θ2 is the phase of the microwave passing through the measured tube, and θ1 is the phase through the standard liquid). The values of k and B can be obtained through multiple calibrations with multiple different concentrations, and then the concentration can be directly obtained based on the phase difference.
[0004] The RF part of the existing microwave density meter uses discrete devices, and the RF part, AD / DA conversion, phase difference circuit and other parts are all implemented using analog devices. Since analog devices are greatly affected by the environment, the overall system stability is poor; in addition, the existing microwave density meter uses a traditional circuit (mixer) to calculate the phase difference, which is greatly affected by the ambient temperature. When the strength of the two mixing signals does not match, the phase difference error is very large, so that the stability is very poor during actual operation, causing the existing products to be extremely unstable and the sold products to be recalled. Utility Model Content
[0005] In order to solve the problems that the existing microwave concentration meter is greatly affected by the environment and the ambient temperature, has poor stability and has a large phase difference calculation error, the utility model proposes a microwave liquid concentration measuring device to solve the above problems.
[0006] The present application discloses a microwave liquid concentration measuring device, comprising a measuring tube, a receiving antenna and a transmitting antenna are respectively arranged on both sides of the measuring tube, the receiving antenna and the transmitting antenna are connected to a radio frequency transceiver unit, and two groups of radio frequency transceiver modules are arranged on the radio frequency transceiver unit, wherein the first group of radio frequency transceiver modules comprises a first transmitting module connected to the receiving antenna and a first receiving module connected to the transmitting antenna, and the second group of radio frequency transceiver modules comprises a second transmitting module, and the second transmitting module is connected to an attenuator, and the attenuator is connected to the second receiving module;
[0007] Since the dielectric constant of the fluid varies greatly at different temperatures, a temperature sensor is added for compensation. The temperature sensor is set on the wall of the measuring tube and is connected to a data processing and control unit.
[0008] The radio frequency transceiver unit is connected to the data processing and control unit.
[0009] The present application adopts two-way RF transceiver, one way passes through the receiving antenna, the measuring tube and the transmitting antenna, and the other way passes through the attenuator. The phase difference is obtained by comparing the waveforms of the two signals. Since both signals pass through the RF transceiver of the same chip and are affected by the same environment, the error caused by the system will be offset when the phase difference is calculated, thereby improving stability.
[0010] Preferably, the radio frequency transceiver unit includes an AD936x chip and an FPGA, the two groups of radio frequency transceiver modules are arranged on the AD936x chip, and the FPGA is connected to the data processing and control unit.
[0011] Preferably, in order to solve the problem that the ambient temperature has a great influence on the crystal oscillator frequency, the AD936x chip is connected to a constant temperature crystal oscillator.
[0012] Preferably, the data processing and control unit comprises a data processing board, and the data processing board is connected to a keyboard module and a display module.
[0013] Beneficial effects of the utility model:
[0014] 1. The utility model adopts AD936x chip to complete the radio frequency transmission and reception, and the analog signal processing part is completed in a single chip, which greatly reduces the impact of the environment on the system and improves the system stability.
[0015] 2. The use of AD936x chips avoids the shortcomings of complex circuit design, difficult system debugging, and poor overall reliability when using discrete devices.
[0016] 3. The phase difference is realized by digital processing. The two channels of AD sampling data received by AD936x are obtained directly through attenuation on one channel and through the measuring tube on the other channel. The data processing unit performs undersampling, digital filtering, FFT transformation, etc. Finally, the phase difference is calculated by software, which abandons the traditional circuit method of calculating the phase difference and avoids the disadvantage of insufficient stability of the traditional circuit.
[0017] 4. Add a constant temperature crystal oscillator to reduce the frequency variation of the generated RF signal and improve the phase difference accuracy.
[0018] 5. Microwave technology is used to adapt to changes in large pipeline diameters, and the measured concentration range is larger. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 This is a schematic structural diagram of a microwave liquid concentration measuring device according to an embodiment of the utility model;
[0020] Figure 2 This is a schematic diagram of the working process of the microwave liquid concentration measuring device according to an embodiment of the utility model. DETAILED DESCRIPTION
[0021] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples.
[0022] like Figure 1 As shown, the embodiment of the present application discloses a microwave liquid concentration measuring device, including a measuring tube 1, a receiving antenna 2 and a transmitting antenna 3 are respectively arranged on both sides of the measuring tube 1, the receiving antenna 2 and the transmitting antenna 3 are connected to a radio frequency transceiver unit 10, and the radio frequency transceiver unit 10 is provided with two groups of radio frequency transceiver modules, wherein the first group of radio frequency transceiver modules includes a first transmitting module 5 connected to the receiving antenna 2 and a first receiving module 9 connected to the transmitting antenna 3, and the second group of radio frequency transceiver modules includes a second transmitting module 6, and the second transmitting module 6 is connected to an attenuator 7, and the attenuator 7 is connected to the second receiving module 8;
[0023] The solution of this embodiment adopts two-way RF transceiver, one way passes through the receiving antenna 2, the measuring tube 1 and the transmitting antenna 3, and the other way passes through the attenuator 7. The phase difference is obtained by comparing the two signals. Since the two signals are both transmitted through the RF transceiver of the same chip and the environmental influences are consistent, the error caused by the system will be offset when the phase difference is calculated, thereby improving stability.
[0024] Since the dielectric constant of the fluid varies greatly at different temperatures, a temperature sensor 4 is added for compensation. The temperature sensor 4 is arranged on the wall of the measuring tube 1 and is connected to the data processing and control unit 11 through a coaxial cable.
[0025] The RF transceiver unit 10 is connected to the data processing and control unit 11. The RF transceiver unit 10 includes an AD936x chip 101 and an FPGA 102. Two groups of RF transceiver modules are arranged on the AD936x chip 101. The FPGA 102 is connected to the data processing and control unit 11 via a USB.
[0026] In order to solve the problem that the ambient temperature has a great influence on the crystal oscillator frequency, the embodiment of the present application adopts a constant temperature crystal oscillator, and the constant temperature crystal oscillator is connected to the mixer in the AD936x chip 101 to reduce the influence of the environment on the crystal oscillator frequency.
[0027] The data processing and control unit 11 comprises a data processing board, and the data processing board is connected with a keyboard module and a display module.
[0028] like Figure 2 The flowchart of the embodiment of the present application is shown. In a specific embodiment, the pulp concentration is measured, the AD936x chip 101 uses AD9361, the FPGA uses Spartan-675K, and the data processing board uses Raspberry Pi 4b. The specific process is as follows:
[0029] When powered on, the processor in the data processing board will download the FPGA program to the FPGA, configure the AD9361, and complete the system startup. The data processing board sets the frequency of the transmitted fundamental wave through configuration, generates the transmitted wave data, and sends the generated data to FPGA102. FPGA102 performs up-conversion processing on the fundamental wave data and sends the converted fundamental wave data to AD9361. After receiving the fundamental wave signal data, AD9361 performs D / A conversion on the data through a digital-to-analog converter (DAC) to generate analog data, which is then mixed with the carrier frequency to generate a transmit signal.
[0030] The transmission signal is divided into two paths. One path is amplified by the gain amplifier and sent to the first transmission module 5, and then sent through the receiving antenna 2 and the transmitting antenna 3; the other path is sent to the second transmission module 6, and then sent to the attenuator 7. The first receiving module 9 receives the signal output by the transmitting antenna 3, and the second receiving module 8 receives the signal output by the attenuator 7. AD9361 first amplifies the two signals by a low noise amplifier (LNA), and then mixes them with the local oscillator frequency through a mixer to restore the baseband. After filtering, the signal is sampled by an analog-to-digital converter (ADC), and the two sampling data are sent to FPGA102.
[0031] The FPGA down-converts the two-channel sampled data and then sends them to the processor in the data processing board.
[0032] After the processor receives the two-channel echo sampling data, it compares the two channels of echo data, first performs digital filtering and FFT transformation, and calculates the phase difference. When calculating the phase difference, due to the large amount of data and the small change in the phase difference within 1 second, only half or less of the data per second is processed to calculate the phase difference, and then the average is taken, which can greatly reduce the amount of data processing without affecting the results.
[0033] At the same time, the processor has been acquiring the AD data of the temperature sensor 4 through AD sampling, and obtaining the pipeline fluid temperature through conversion. The processor finally calculates the pulp concentration based on the phase difference and the current pipeline temperature, and then sends the pulp concentration to the display module for display. The processor converts the concentration into 4-20ma through DA conversion and outputs it to the valve control system. The time and parameter settings are completed through the keyboard module, and calibration can also be performed.
[0034] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and descriptions are only for explaining the principle of the utility model. Without departing from the spirit and scope of the utility model, the utility model may have various changes and improvements, which fall within the scope of the utility model to be protected. The scope of protection of the utility model is defined by the attached claims and their equivalents.
Claims
1. A microwave liquid concentration measuring device, It is characterized in that The measuring tube (1) comprises a receiving antenna (2) and a transmitting antenna (3) respectively arranged on both sides of the measuring tube (1), the receiving antenna (2) and the transmitting antenna (3) are connected to a radio frequency transceiver unit (10), and the radio frequency transceiver unit (10) is provided with two groups of radio frequency transceiver modules, wherein the first group of radio frequency transceiver modules comprises a first transmitting module (5) connected to the receiving antenna (2) and a first receiving module (9) connected to the transmitting antenna (3), and the second group of radio frequency transceiver modules comprises a second transmitting module (6), the second transmitting module (6) is connected to an attenuator (7), and the attenuator (7) is connected to a second receiving module (8); A temperature sensor (4) is arranged on the wall of the measuring tube (1), and the temperature sensor (4) is connected to a data processing and control unit (11); The radio frequency transceiver unit (10) is connected to a data processing and control unit (11).
2. The microwave liquid concentration measuring device according to claim 1, It is characterized in that The radio frequency transceiver unit (10) comprises an AD936x chip (101) and an FPGA (102); the two groups of radio frequency transceiver modules are arranged on the AD936x chip (101); and the FPGA (102) is connected to a data processing and control unit (11).
3. The microwave liquid concentration measuring device according to claim 2, It is characterized in that The AD936x chip (101) is connected to a constant temperature crystal oscillator.
4. The microwave liquid concentration measuring device according to claim 3, It is characterized in that The data processing and control unit (11) comprises a data processing board, and the data processing board is connected to a keyboard module and a display module.