We will investigate the measuring principle of time-of-flight (TOF) ultrasonic level meter, related analysis and comparison of performance and modification method. Higher measuring precision of height at 0.1mm order of magnitude, and algorithm robustness in the case of weak surface movement, are expected. When using absolute transit time algorithm, the head of wave should be clear, by eliminate echo faster than that through main wave path. And in second trace echo case, ensure there are parts of two echo waves, can be located by theoretical arithmetic and waveform algorithm, have higher relevancy than 98%. In order to enhance the precision of ultrasonic level meter, a proper transit time algorithm will be selected and optimized. The systematic time deviation and delay, transit time in protective containment, cable delay and circuit running time, will be estimated, then adjusted in stable water. The speed of sound, to modify level results with high precision TOF, in objective experimental environment can be calibrated by manometer and thermometer, in pure water media, fluctuation of sound speed measured by ultrasonic apparatus and transfer from temperature is smaller than 0.01%. Finally, micrometer and pressure meter will be used, to compare and evaluate the precision, stability and linearity of level meter, in stable and moving water.
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