FAURE HERMAN FH8400, User Manual

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Chapter 1: General overview
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The velocity of flow along the path between two paired
transducers is determined by the method called "Transit Time
Difference Method" based on the expression below:
B
T T
∆T
2.cos
V
L
Α
⋅
ΒΑ
⋅ =
θ
where
AB BA
T T ∆T
− =
(T
AB
: transit time of the ultrasonic wave from the upstream
transducer to the downstream; T
BA
: transit time of the ultra-
sonic wave from the downstream transducer to the upstream.
Remark: The expression above is independent of the velocity of sound inside
the product flowing in the pipe.
This velocity can be computed by the meter by using the following expression:






+ =
BA
T
1
AB
T
1
2
L
C
upstream
transducer (A)
downstream
transducer (B)
D
direction of flow
L