Transit time difference method
Among the different ultrasonic methods used for the measurement of fluid velocity, the method of the” transit time difference ” is the most accurate and the only one which permits to realize a true integration of velocity profile along the acoustic path.
According to the flow hydraulic conditions and to the required accuracy, one or several chords can be used (a chord is composed of 2 probes)
There are two successive operations in the flow measurement
• The velocity measurement on one or several chords
• the flow calculation from one or several velocity measurements
The process advantages
• is independant of the sound velocity in the fluid
• is bidirectional
• no provides pressure drop
This measurement principle is applicable to liquids and gas.
The used probes can be intrusive or external (clamp-on).