压电式超声波换能器测试方法的研究与设计

发布时间：2019-01-27 07:30

【摘要】：超声波流量计广泛应用在水、热量及燃气等流量计量中,其中超声波换能器是超声波流量计的核心部件。在实际流量计量应用中,时差法是采用最多的一种测试方法。时差法超声波流量计所用的换能器需要成对使用,其性能匹配直接影响时差法超声波流量计的流量计量精确度。目前对于超声波流量计所用换能器性能评价没有统一的技术标准支撑,许多流量计生产企业忽视对成对换能器性能匹配的研究,往往只是凭借经验对换能器进行匹配使用。针对超声波换能器主要参数性能一致性差的问题,本课题对超声波换能器进行性能参数测试研究,提出测试换能器的谐振频率与反谐振频率、谐振阻抗与反谐振阻抗、输出幅值、静态电容六种参数指标的测试与分析方法,旨在为超声波流量计量提供成对且性能参数相匹配的换能器。本文主要研究内容如下:首先,从时差法超声波流量计工作原理出发,对影响时差法流量计量精确度的因素进行分析,着重分析超声波信号在流体中传输时对信号质量的影响及超声波信号对阈值检测法与过零检测法相结合方案的计时精确度的影响等问题;其次,建立薄圆片厚度振动模式换能器的等效电路,利用Matlab及数学方法仿真换能器收发特性,从而分析出谐振频率与反谐振频率、谐振阻抗与反谐振阻抗及静态电容对换能器输出幅值的影响,为配对换能器性能一致性提供理论依据;最后,以FPGA为主控芯片搭建换能器参数测试装置,针对传输线路法对信号发生器要求具有较宽输出频率范围的问题,基于直接数字频率合成技术方法,设计宽范围频率输出信号发生器。针对输出幅值测试激励信号频率无法调节、需要人工读取数据等问题,本文采用可变频的激励信号,对换能器输出幅值进行测试。为了解决LCR数字电桥测量静态电容存在测量速度慢、抗杂散电容能力弱等问题,本文采用容抗法对静态电容进行测量,具有快速测量及自动调零功能。通过对换能器参数测试来评价换能器性能,从而达到成对换能器性能匹配的目的。经过实验验证,本课题采用的参数测试方法满足设计要求,通过对换能器六种参数测试,验证流量计所用配对换能器性能的一致性。并通过对不同温度下换能器参数的测试,验证换能器参数的温度稳定性。
[Abstract]:Ultrasonic Flowmeter is widely used in water, heat and gas flow measurement, among which ultrasonic transducer is the core component of ultrasonic Flowmeter. In the application of actual flow measurement, the moveout method is one of the most widely used test methods. The transducer used in the time difference ultrasonic Flowmeter needs to be used in pairs, and its performance matching directly affects the accuracy of the flow measurement of the moveout ultrasonic Flowmeter. At present, there is no uniform technical standard support for the performance evaluation of the transducer used in ultrasonic Flowmeter. Many Flowmeter manufacturers ignore the research on matching the performance of the pair transducer, and often use the transducer only by experience. In order to solve the problem of poor consistency of the main parameters of ultrasonic transducer, the performance parameters of ultrasonic transducer are tested and studied in this paper, and the resonant frequency and anti-resonance frequency, resonance impedance and anti-resonance impedance of ultrasonic transducer are tested. The measurement and analysis method of six parameters of output amplitude and static capacitance is designed to provide a pair of transducers with matching performance parameters for ultrasonic Flowmeter. The main contents of this paper are as follows: firstly, based on the working principle of the moveout ultrasonic Flowmeter, the factors affecting the accuracy of the moveout flow measurement are analyzed. The influence of ultrasonic signal transmission in fluid on the signal quality and the influence of ultrasonic signal on the timing accuracy of the combination of threshold detection and zero-crossing detection are analyzed. Secondly, the equivalent circuit of the thin disk thickness vibration mode transducer is established, and the transceiver characteristics of the transducer are simulated by Matlab and mathematical methods, and the resonant frequency and the antiresonant frequency are analyzed. The influence of resonant impedance, antiresonant impedance and static capacitance on the output amplitude of the transducer provides a theoretical basis for matching the performance consistency of the transducer. Finally, taking FPGA as the main control chip, the transducer parameter testing device is built. Aiming at the problem that the transmission line method requires a wide output frequency range for the signal generator, the direct digital frequency synthesis technology is used to solve the problem. Design a wide range of frequency output signal generator. Aiming at the problem that the frequency of the output amplitude test excitation signal can not be adjusted and the data need to be read manually, the output amplitude of the transducer is tested by frequency conversion excitation signal in this paper. In order to solve the problems of low measuring speed and weak ability of resisting stray capacitance in LCR digital bridge measuring static capacitance, this paper uses capacitive reactance method to measure static capacitance, which has the function of fast measurement and automatic zero adjustment. The performance of the transducer is evaluated by measuring the parameters of the transducer to match the performance of the pair transducer. The experimental results show that the parameter measurement method adopted in this paper meets the design requirements. The performance consistency of the matched transducer used in the Flowmeter is verified by testing the six parameters of the transducer. The temperature stability of the transducer parameters is verified by testing the transducer parameters at different temperatures.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB552

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