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In this paper,the usual pulse echo overlap method for ultrasonic wave velocity measurement isdeveloped to pulse echo overlap method with alternative triggering.The principle of the method liesin that,when the first ultrasonic echo train,being given rise from the first transmitting pulse,is dis-played on an oscilloscope,the oscilloscope is triggered normally and synchronized with the transmittingpulse.But for the next echo train to be displayed,which is given rise from the second transmittingpulse,it will be triggered after a further time delay than that of the first one,which is equal to a roundtrip time of an ultrasonic pulse in the sample.Then the whole procedure is repeated again and againand on the oscilloscope a pattern of overlapped echo trains can be observd.The value of the delaytime can be obtained directly from a digital counter.By changing the scanning rate of the oscilloscopeand adjusting its triggering delay,any part of the overlapped pattern can be observed and studied. Based on this princi 相似文献
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利用超声方法测定北京大钟寺永乐古钟的壁厚 总被引:1,自引:0,他引:1
利用超声测厚的方法第一次测定了北京永乐古钟的壁厚。由于采用了交叉触发脉冲重叠法以及适当调节工作频率,从而解决了测量中的实际困难。测量精度约为1.5%。还根据测得大钟的直径和密度,计算出大钟连同其挂钩在内的总重量约为46.6±1吨。 相似文献
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查济璇 《声学学报:英文版》1987,(2)
The Pulse-Echo-Overlap method(PEO method)has now been considered as the most adequatemethod for accurate measurement of the absolute value of ultrasonic velocity.For this accurate timemeasurement,it is essential to find the time delay and implement its corrections,e.g.the correction ofreflection time delay,the correction of diffraction time delay,etc.To overcome the inconvenience of thewidely used in practice method of reflection time delay calculation,and its imperfection in theory,a newcalculation procedure of the reflection time delay correction is worked out in this paper,and an experimentaldetermination method for its value by means of double crystal is suggested.This paper further suggests aparameter of the period increment of zero phase shift Δτ_r,and considers it as an experimental constant,whose value is about 1.7 ns in practical applications. Furthermore,this paper suggests a criterion of correct overlap.If the echoes are correctly overlapped,the slope of the curve of the ultrasonic wave tri 相似文献
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脉冲回波重合法(PEO法)目前已被公认为精密测定声速绝对值的最适用方案。为了使该法所具有的高精度测时能力起到实际效果,必须把其中所包含的反射时延、衍射时延等修正值相应地推求出来,加以修正。至今所广泛采用的反射时延计算方法,在实用上仍有所不便,在理论上也不尽准确,为此,本文进一步作了分析。 本文得出了包括衍射影响在内的反射相移时延修正值的计算方法。并提出了一种双晶片法实验测定修正值的方案。本文并提出取零相移周期增量Δг,作为实验常数,其值在一般情况下约为1.7~(ns),这样对实用就更为简便。 本文还提出了一种判别准确重合的方案。当准确重合时,测得声时一周期曲线的斜率为—h。 相似文献
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本文对原来测量超声声速的脉冲回波重叠法发展改进为交叉触发脉冲回波重叠法.即在示波器上显示脉冲回波时,前一次发射脉冲所产生的一组反射脉冲波列,按正常情况触发显示,而紧随的下一次发射脉冲所产生的一组反射脉冲波列,在触发时刻上,比正常情况延后一个时间值,其值等于超声脉冲在样品中来回一次的时间,如此循环.因而在示波器屏上就可看到整个反射波列相应地一一重叠的波形.其延后的时间值,可由数字式频率计读出.再籍调节示波器的扫描速度及扫描延时,即可很方便地观察重叠波形中的任何部分. 我们还利用这种测量方案,研制成了一种适用于液体的声速仪,可直接读得声速值,使用灵便. 相似文献
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本文从基本的压电Christoffel方程出发导出三角晶系3m点群压电晶体弹性常数的表示式。并采用10MHz射频超声脉冲回波重合法测量了沿LiNbO_3不同对称方向传播的声速,结合e_(ij)和ε_(ij)~5给出了LiNbO_3全部弹性常数C_(ij)~E和C_(ij)~D。它们是 C_(11)~E=19.89,C_(12)~E=5.25,C_(13)~E=7.81,C_(14)~E=0.96, C_(33)~E=25.44,C_(44)~E=6.10,C_(66)~E=7.32×10~(10)N/m~2, C_(11)~D=21.51,C_(12)~D=3.65,C_(13)~D=7.91,C_(14)~D=-1.41, C_(33)~D=26.10,C_(44)~D=9.62,C_(66)~D=8.93×10~(10)N/m~2。 相似文献