PULSE ECHO OVERLAP METHOD WITH ALTERNATIVE TRIGGERING AND LIQUID VELOCIMETER

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     

用脉冲重叠法精确测定表面声波的传播速度

本文提出采用交叉触发脉冲重叠法来精确测定材料的表面声波相速度.在一块样品上制作相同的三个叉指换能器A、B、C,在B与C之间的样品表面镀上金属膜.分别依次由A或C发射表面声波,而由其它两个换能器接收,即可测定表面声波的速度和速度变化.本文对LiNbO,石英及压电陶瓷样品进行了测量,测量精度估计约为±2m/s.     

利用超声方法测定北京大钟寺永乐古钟的壁厚

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。     

交叉触发脉冲回波重叠法及其基于本法的液体声速仪

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.