A method to avoid the cycle-skip phenomenon in time-of-flight determination for ultrasonic flow measurement

The double-threshold method has been widely used in ultrasonic flow measurement to determine time-of-flight(TOF)due to its low cost and ease of implementation.Performance of this method is negatively affected by the cycle-skip phenomenon which occurs frequently under inconstant working conditions,especially varied fluid temperature.This paper proposes a method to suppress the phenomenon to facilitate reliable determination of TOF in ultrasonic flow measurement.First,the double-threshold method is used to generate a feature point to segment the signal.Second,based on the correlation coefficient and signal power,judgement factors of individual signal periods are calculated to determine signal onset.Finally,a valid zero crossing which has a constant lag from the onset is selected to determine the TOF.Thus,the cycle-skip phenomenon is suppressed.Two additional modifications are proposed to eliminate the influence of varied signal frequency and low sampling rate.The proposed method was validated by an experiment based on an ultrasonic water flow sensor.Results showed that the frequently appearing cycle-skip phenomenon can be successfully suppressed by the proposed method.

FPGA-based High-precision Measurement Algorithm for the Ultrasonic Echo Time of Flight

Based on the evaluation of advantages and disadvantages of high-precision digital time interval measuring algorithms, and combined with the principle of the typical time-difference ultrasonic flow measurement, the requirements for the measurement of echo time of flight put forward by the ultrasonic flow measurement are analyzed. A new high-precision time interval measurement algorithm is presented, which combines the pulse counting method with the phase delay interpolation. The pulse counting method is used to ensure a large dynamic measuring range, and a double-edge triggering counter is designed to improve the accuracy and reduce the counting quantization error. The phase delay interpolation is used to reduce the quantization error of pulse counting for further improving the time measurement resolution. Test data show that the systexn for the measurement of the ultrasonic echo time of flight based on this algorithm and implemented on an Field Programmable Gate Army（FleA） needs a relatively short time for measurement, and has a measurement error of less than 105 ps.

An assessment on the wideband and narrowband methods for ultrasonic blood flow measurements

A comparison study on the ultrasonic blood flow estimation methods is carried out in this paper. The methods are divided into two classes-narrowband and wideband techniques.The pulsed Doppler systems and the autocorrelation methods are essentially the narrowband estAnators. They give the results with low velocity resolution and probably the aliased spectrum.The wider the frequency band of the signals, the worse the results. Time domain crosscorrelation technique, wideband makimum likelihood estimation and 2D Fourier transform method are three wideband techniques. The high velocity resolution and the ability of anti-aliasing are shown by these wideband estimation strategies.

Experimental Modelling of the Impact of a DC Magnetic Field on the Melt Flow in a Continuous Casting Mould

This paper describes experimental investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field at laboratory scale.Experimental results will be presented here which have been obtained using a physical model(mini-LIMMCAST)operating with the low melting point alloy GaInSn.According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the Submerged Entry Nozzle(SEN)has been studied up to Hartmann numbers of about 400.The Ultrasound-Doppler-Velocimetry(UDV)was applied for measurements of the flow pattern in the mould.Local conductivity anemometers were used to measure the turbulent quantities of the flow.The effect of the magnetic field on the flow structure turned out to be manifold and rather complex.The magnetic field causes a deflection of the jet,at which the respective exit angle from the nozzle ports becomes more flat.Thus,both the penetration depth of the discharging flow into the lower part of the mould and the impinging velocity of the jet onto the side wall are reduced.A significant return flow occurs in the adjacent regions of the jet.Specific vortices are formed with axes being aligned with the magnetic field direction.Such vortical structures are typical for quasi-two-dimensional magneto-hydrodynamic(MHD)flows.The flow measurements do not manifest a general braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume.Variations of the wall conductivity showed a striking impact on the resulting flow structures.