A6.4 - Wave Propagation Phenomena in Case of Clamp-On Ultrasonic Systems Applied on Liquid Filled Pipes

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A6 - Ultrasonic Sensors I
S. Wöckel, U. Hempel, J. Auge - IFAK Institut für Automation und Kommunikation e. V. Magdeburg (Germany)
153 - 158


Ultrasonic measurements are common techniques in industrial liquid analysis. Especially the non-invasive clamp-on configuration is an interesting approach due to its non-destructive nature and easy handling. Such a sensor can be mounted on existing reactors or pipes without stopping the process or rebuilding the system. However, such a technique often needs a sophisticated signal analysis in order to discriminate the measurement effect from disturbances caused by the multimodal sound propagation. The disturbing signals occur from wave propagation within the pipe wall, the ringing due to low damping and from mode conversions at the solid-liquidinterfaces. As consequence of these disturbance signals typically the clamp-on liquid analysis is carried out for a few cases only, e.g. for concentration measurements of homogeneous media or homogeneous distributed particles. Even multiphase systems are not handled by reason of the varying acoustic impedance at the inner pipe wall. All systems
need a calibration of sensor position and time windowing also. To enhance the performance and reliability of clampon ultrasonic applications towards analysis tasks, a sophisticated signal analysis and knowledge of the wave behaviour, the mode conversion and the influence of dispersion within the large scale complex technical structure with a high precision is required. In order to design such a robust sensor system a tool is needed that estimates the behaviour of multimodal sound propagation within a pipe prior to the sensor setup and measurement process.
This paper discusses the multimodal sound wave propagation in small up to large scale pipes filled with multiphase liquid systems. A first estimation of expected wave propagation paths, corresponding travel time and multiple reflections is performed using the Mason-theory. It will be shown that this linear modelling is adequate to choose proper time windows in the acquired ultrasonic signals where no significant disturbing effects caused by multiple reflections and dispersive solid state waves occur. The paper further presents FEM-analyses in combination with experimental studies that are used to investigate the influence of the mode conversion depending on liquid loading, the changing pipe wall thickness or temperature changes on the signals behaviour. Exemplarily a clamp-on configuration with a sample signal and the reflection signal from a liquid interface and the disturbing signals are shown.