Kamstrup ULTRAFLOW 54 H, Technical Description

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ULTRAFLOW® 54 (H)/(J)
Kamstrup A/S ∙ Technical Description ∙ 5512‐1554_J1_GB _04.2018 39
v
is the average flow velocity of water [m/s]
The transit time difference can be expressed as the difference between the absolute time of the signal sent against
the flow (-) and the signal sent with the flow (+).
v c
l
v c
l
t



 
which can also be written as:
2 2
2
) )( (
) ( ) (
v c
v
l t
v c v c
v c v c
l t

  
 
  
 
As
2 2
v c

,
2
v
can be omitted and the formula reduced as follows:
l
c t
v
2
2
 

Thus, we know the basic connection between the average flow velocity and the transit time difference.
The transit time difference in a flow sensor is very small (nanoseconds). Therefore, the time difference is measured
as a phase difference between the two 1 MHz sound signals to obtain the necessary accuracy.
Furthermore, the influence of the temperature of the sound velocity of water must be taken into account. In
ULTRAFLOW
®
the velocity of ultrasound
c
is measured by means of a number of absolute time measurements
between the two transducers. As the geometry of the flow sensor is known the measured velocity of ultrasound is
thus a measurand for the water temperature, which is further utilized in the built-in ASIC in connection with flow
calculations.
The flow (volume flow rate) is then determined by measuring the transit time difference, calculating the average
flow velocity and multiplying it by the area of the measuring tube:
A v q
 
where:
q
is the flow (volume flow rate)






h
m
3
A
is the area of the measuring pipe
 
2
m
The volume
V
passing through is finally calculated as time integration over the flow (multiplication of (cross
section constant) flow by time).