When the ultrasonic beam propagates in the liquid, the flow of the liquid will cause minute changes in the propagation time, and the change in the propagation time is proportional to the flow rate of the liquid. The relationship is in accordance with the following expression:
among them
θ is the angle between the sound beam and the direction of liquid flow
M is the number of straight propagations of the sound beam in the liquid
D is the inner diameter of the pipe
Tup is the propagation time of the sound beam in the positive direction
Tdown is the propagation time of the sound beam in the reverse direction
ΔT=Tup –Tdown
Let the sound velocity in the stationary fluid be c, the velocity of the fluid flow be u, and the propagation distance be L. When the sound wave and the fluid flow are in the same direction (that is, in the forward flow direction), the propagation velocity is c+u; otherwise, the propagation velocity is cu. Two sets of ultrasonic generators and receivers (T1, R1) and (T2, R2) were placed at two locations apart from each other by L. When T1 goes in the forward direction and T2 transmits ultrasonic waves in the reverse direction, the time required for the ultrasonic waves to reach the receivers R1 and R2 respectively is t1 and t2.
T1=L/(c+u); t2=L/(cu)
Because in the industrial pipeline, the flow velocity of the fluid is much smaller than the speed of sound, ie c>>u, the time difference between the two is â–½t=t2-t1=2Lu/cc. From this it can be seen that when the sound wave travels in the fluid, the velocity c When it is known, the flow rate u can be obtained by measuring the time difference â–½t, and the flow rate Q can be obtained. The method for measuring the flow rate using this principle is called the time difference method.
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500mm Stretch Film Machine Unit
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