Kamstrup ULTRAFLOW 54 Technical Description page 36

TECHNICAL DESCRIPTION
In principle, flow is determined by measuring the flow velocity and multiplying it by the area of the measuring
pipe:
Q = F × A
where:
Q
is the flow
F
is the flow velocity
A
Is the area of the measuring pipe
The area and the length, which the signal travels in the sensor, are well-known factors. The length which the signal
travels can be expressed as
L
T =
V
where:
L
is the measuring distance
V
is the sound propagation velocity
T
is the time
The time can be expressed as the difference between the signal sent with the flow and the signal sent against the
flow.
 
1 1
   
∆ T = L × −
 V V 
1 2
In connection with ultrasonic flow sensors the velocities
V = C − F V = C
And
1 2
where:
C
is the velocity of sound in water
Using the above formula you get:
1 1
∆ T = L × −
− +
C F C
which can also be written as:
( C + F ) − ( C
∆ T = L ×
( C − F ) × ( C
C 〉〉
2 2 2
F F
As , can be omitted and the formula reduced as follows:
2
∆ T × C
F =
× 2
L
In order to minimize the influence from variations of the velocity of sound in water, the velocity is measured via a
number of absolute time measurements between the two transducers. These measurements are subsequently, in
the built-in ASIC, converted into the current velocity of sound which is used in connection with flow calculations.
36
L = T × V
, which can also be written as:
+ F
respectively
F
− F )
⇒
∆ T = L ×
+ F )
5512-385 GB/02.2014/Rev. H1
V V
and can be stated as:
1 2
2 F
2 2
C − F
®
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