Tokyo Keiki UFL-30, Installation & Operation Manual

Page: 146 / 166

III- 37
III-3. Principles of the Ultrasonic Flowmeter
III-3-1 Measurement principles
φ
1
φ
2
φ
3
φ
θ
L
Velocity V
Flow direction
d
P1
P2
Sensor
Wedge
Transducer
Lining
Pipe wall
Fig. 3-1; Ultrasonic Wave Propagation Route
A sensor (called "Transducer") consists of an transducer for transmitting and receiving
ultrasonic waves and a plastic wedge. Transducers P1 and P2 have the same structure
and characteristics.
When an ultrasonic pulse is transmitted from the transducer of transducer P1, the pulse is
propagated through the wedge and strikes the boundary with the pipe wall at angle
φ
1.
The wave is then refracted and propagated through the pipe wall at angle
φ
2.
The pulse then passes through the lining at refraction angle
φ
3 and through the fluid at
refraction angle
φ
.
When the velocity of sound is defined as C1 in the wedge, C2 in the pipe wall, C3 in the
lining, and C in the fluid, the following formula can be deduced from the law of refraction.
C C C C
   
sin
3
3 sin
2
2 sin
1
1 sin
  
(1)
The ultrasonic pulse propagated through the fluid reverses the previous path (fluid
→
lining
→
pipe wall) and is received by transducer P2. The received pulse is then converted into an
electronic pulse.
The following formula can be written when the propagation time of an ultrasonic pulse from
P1 to P2 (in other words the positive direction of the fluid) is defined as td.