發(fā)布時(shí)間：2019-01-27 07:30

【摘要】：超聲波流量計(jì)廣泛應(yīng)用在水、熱量及燃?xì)獾攘髁坑?jì)量中,其中超聲波換能器是超聲波流量計(jì)的核心部件。在實(shí)際流量計(jì)量應(yīng)用中,時(shí)差法是采用最多的一種測(cè)試方法。時(shí)差法超聲波流量計(jì)所用的換能器需要成對(duì)使用,其性能匹配直接影響時(shí)差法超聲波流量計(jì)的流量計(jì)量精確度。目前對(duì)于超聲波流量計(jì)所用換能器性能評(píng)價(jià)沒(méi)有統(tǒng)一的技術(shù)標(biāo)準(zhǔn)支撐,許多流量計(jì)生產(chǎn)企業(yè)忽視對(duì)成對(duì)換能器性能匹配的研究,往往只是憑借經(jīng)驗(yàn)對(duì)換能器進(jìn)行匹配使用。針對(duì)超聲波換能器主要參數(shù)性能一致性差的問(wèn)題,本課題對(duì)超聲波換能器進(jìn)行性能參數(shù)測(cè)試研究,提出測(cè)試換能器的諧振頻率與反諧振頻率、諧振阻抗與反諧振阻抗、輸出幅值、靜態(tài)電容六種參數(shù)指標(biāo)的測(cè)試與分析方法,旨在為超聲波流量計(jì)量提供成對(duì)且性能參數(shù)相匹配的換能器。本文主要研究?jī)?nèi)容如下:首先,從時(shí)差法超聲波流量計(jì)工作原理出發(fā),對(duì)影響時(shí)差法流量計(jì)量精確度的因素進(jìn)行分析,著重分析超聲波信號(hào)在流體中傳輸時(shí)對(duì)信號(hào)質(zhì)量的影響及超聲波信號(hào)對(duì)閾值檢測(cè)法與過(guò)零檢測(cè)法相結(jié)合方案的計(jì)時(shí)精確度的影響等問(wèn)題;其次,建立薄圓片厚度振動(dòng)模式換能器的等效電路,利用Matlab及數(shù)學(xué)方法仿真換能器收發(fā)特性,從而分析出諧振頻率與反諧振頻率、諧振阻抗與反諧振阻抗及靜態(tài)電容對(duì)換能器輸出幅值的影響,為配對(duì)換能器性能一致性提供理論依據(jù);最后,以FPGA為主控芯片搭建換能器參數(shù)測(cè)試裝置,針對(duì)傳輸線路法對(duì)信號(hào)發(fā)生器要求具有較寬輸出頻率范圍的問(wèn)題,基于直接數(shù)字頻率合成技術(shù)方法,設(shè)計(jì)寬范圍頻率輸出信號(hào)發(fā)生器。針對(duì)輸出幅值測(cè)試激勵(lì)信號(hào)頻率無(wú)法調(diào)節(jié)、需要人工讀取數(shù)據(jù)等問(wèn)題,本文采用可變頻的激勵(lì)信號(hào),對(duì)換能器輸出幅值進(jìn)行測(cè)試。為了解決LCR數(shù)字電橋測(cè)量靜態(tài)電容存在測(cè)量速度慢、抗雜散電容能力弱等問(wèn)題,本文采用容抗法對(duì)靜態(tài)電容進(jìn)行測(cè)量,具有快速測(cè)量及自動(dòng)調(diào)零功能。通過(guò)對(duì)換能器參數(shù)測(cè)試來(lái)評(píng)價(jià)換能器性能,從而達(dá)到成對(duì)換能器性能匹配的目的。經(jīng)過(guò)實(shí)驗(yàn)驗(yàn)證,本課題采用的參數(shù)測(cè)試方法滿足設(shè)計(jì)要求,通過(guò)對(duì)換能器六種參數(shù)測(cè)試,驗(yàn)證流量計(jì)所用配對(duì)換能器性能的一致性。并通過(guò)對(duì)不同溫度下?lián)Q能器參數(shù)的測(cè)試,驗(yàn)證換能器參數(shù)的溫度穩(wěn)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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB552

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