Abstract-A new method for measuring the pressure reflection coefficient in a buffer rod configuration is presented, together with experimental results for acoustic measurements of the liquid density, based on the measurement of the liquid's acoustic impedance. The method consists of using 2 buffers enclosing the liquid in a symmetrical arrangement with a transducer fixed to each buffer. One of the transducers is used in a pulse-echo mode while the other transducer operates as a receiver. The echo amplitudes leading to the pressure reflection coefficient as found by this method possess advantages such as reduced attenuation due to a shorter liquid transmission path and reduced interference, as compared with the ABC method. Measurements with distilled water and with special density calibration oil qualities have been performed using both the new method and the ABC method and are shown for the new method to give a density span within 0.15% of the reference values. A comparison of the measured densities based on both a time-domain and a l 2 -norm frequency domain integration signal processing approach is given, along with a recommendation as to how the signal processing should be performed.
Abstract-The known acoustic methods for obtaining the pressure reflection coefficient from a buffer rod based measurement cell are presented, along with 2 new generic approaches for measuring the pressure reflection coefficient using 2 buffer rods enclosing the liquid to be characterized in a symmetrical arrangement. An acoustic transducer is connected to each of the buffer rods. The generic approaches are divided into a relative amplitude approach and a mixed amplitude approach. For the relative amplitude approach, families of 4, 5, or 6 echo signals can be used to obtain the pressure reflection coefficient. The mixed amplitude approach uses specific information about the transducers and/or the electronics sensitivities in receive mode to obtain the pressure reflection coefficient using families of 3, 4, 5, or 6 echo signals. Some of the new methods from the relative amplitude approach imply a reduced uncertainty relative to the previously known ABC method. The effect of the liquid attenuation, digitizer bit resolution, and the signal-to-noise ratio on the uncertainty characteristics of the pressure reflection coefficient are discussed, along with a discussion of the suitability of the various methods for different buffer materials.
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