| Ultrasonic technology has been widely used in the field of oil and gas flow detection.The piezoelectric transducer is the core component of ultrasonic flow detection.However,as the working environment changes,the characteristics of the transducer will also change,which will affect the driving efficiency of the acoustic wave and the strength of the received signal,and ultimately reduce the measurement accuracy of the flowmeter.For the above problems,this paper starts from the equivalent circuit of the transducer first,and through the research and analysis of the existing various types of impedance matching circuits,a dynamic impedance matching scheme based on T-type impedance matching is determined.The dynamic matching of the transducer is achieved by controlling the switching of components.In view of the fact that the energy conversion efficiency of the piezoelectric transducer is easily affected by environmental factors,this paper then designs the hardware part of the impedance matching system of the acoustic wave flowmeter.This part first performs conditioning amplification,AD sampling and zero-crossing comparison processing on the voltage and current signals,and then uses the microcomputer to realize the measurement of impedance mode and impedance angle;on this basis,an automatic impedance matching circuit is further designed,which can be based on real-time detection of impedance information to control the analog switch to switch and gating different component combinations to realize automatic impedance matching.In order to realize the effective extraction of the acoustic wave receiving signal,the hardware part also designs the receive signal conditioning circuit with the function of filtering and amplifying.On the basis of automatic impedance matching and signal conditioning circuit,this paper also designs the control flow and measurement algorithm of the system with MSP430FR6047 as the core.The calculation of system parameters is completed through functional modules such as signal generation,impedance detection and matching,and receive signal acquisition and processing.And follow the logic set by the main program,execute each module sequentially,and then realize the complete measurement of the impedance matching system of the acoustic wave flowmeter.Finally,the cross-correlation algorithm is used to simulate the sampled actual receive signals.The results of the cross-correlation algorithm show that the algorithm can effectively distinguish the time difference between the two signals,and realize high-precision and stable flow measurement.In order to verify the effectiveness of the above-mentioned impedance matching system and determine the specific parameters of the devices in the impedance matching network,detailed experimental research is also carried out in this paper.This paper uses the LCR tester to measure the transducer impedance value at different temperatures,calculates the equivalent circuit parameters of the transducer through the admittance circle,uses Multisim for circuit simulation,observes and analyzes the relationship between the output active power and frequency of the signal source,test data and the simulation results show that the resonant frequency of the transducer will gradually decrease with the increase of temperature,and corresponding impedance matching measures need to be taken to intervene;the temperature experiment results show that the equivalent circuit parameters of the transducer will change with the increase of temperature,the static capacitance and dynamic capacitance increase,and the dynamic inductance and dynamic resistance decrease.In the experimental research,based on the ADS radio frequency circuit software,the design and simulation of several common impedance matching circuits for transducers at different temperatures were completed.The simulation results show that the bandwidth of the T-type matching circuit is narrower,and the reflection coefficient can reach the minimum value at 542k Hz.Therefore,this type of matching circuit is suitable for the dynamic impedance matching design of the acoustic flowmeter.Then use Multisim to simulate the T-type matching circuit.The results show that after the transducer achieves impedance matching at different temperatures,the peak point of the active power of the signal source is mainly concentrated near the 542k Hz resonant frequency,which compensates for the resonant frequency shift of the transducer.Finally,this paper tested the impedance detection performance of the dynamic impedance matching system based on T-type circuit.The results show that at 80°C,the comprehensive measurement error is less than 10%,and the system can realize impedance measurement in high temperature environment.In the environment with a mud density of 1.2g/cm~3,the dynamic impedance matching performance of the transducer at different temperatures is detected,and the maximum gain of the signal reception amplitude after matching is 10.3d B and the minimum is 7.44d B,which meets the requirements of the flowmeter.In addition,the performance of the receiving signal conditioning circuit was tested in oil-based mud with a mud density of 1.721g/cm~3.The signal can be effectively extracted from the noise after passing through the conditioning circuit.The amplitude of the amplified receiving signal is 100m V,which can meet the flow measurement requirements. |
PDF Full Text Request