Thermo Scientific HB-S200, User Manual

Page: 15 / 77

Sarasota 200 Ultrasonic Multipath
Flowmeter
Section 1 INTRODUCTION Page 1-5 Thermo Fisher Scientific
INTRODUCTION
1.2.5.2 Mean section method
In the mean section method, the slice boundaries are defined by the path heights themselves.
The slice velocity is taken as the mean of the upper and lower paths which define the slice
boundaries. The upper boundary of the top slice is the water surface.
The velocity of the water surface, Vs, is given by:-
Vs = V
4
+ (V
4
-V
3
) x Ks(Hs-H
4
)/(H
4
-H
3
)
Where Ks is a multiplying factor normally between 0 and 1 to allow for the projection
of velocity to the water surface
Vs is limited to a value of V
4
+ (V
4
-V
3
) in the event of (Hs-H
4
) being greater than (H
4
-H
3
)
The lower boundary of the bottom slice is the bed. This bottom slice has a weighting factor,
K
B
, normally between 0.4 and 0.8 to allow for the slow moving water near the bed.
The mean section method is superior in cases where the paths are not near the slice centres,
but the mid section method handles the top slice better. The more paths that are deployed,
the less the differences matter.
The mean section method is illustrated in the following diagram:
Illustration of the mean section method for 4 paths
Bed, Height H
0
Wbed
Surface Height H
S
Path 4. Height H
4
Water Surface
W
3
W
2
W
1
Width W
S
W
4
Q
s
= ½(V
S
+ V4) x (H
S
– H
4
) x ½(W
S
+ W
4
)
Q
s
= ½ (V
4
+ V
3
) x (H
4
– H
3
) x ½(W
4
+ W
3
)
Q
s
= ½ (V
3
+ V
2
) x (H
3
– H
2
) x ½(W
3
+ W
2
)
Q
s
= ½V
1
(1 + k
B
) x (H
1
– H
0
) x ½(W
1
+ W
Bed
)
Q
s
= ½ (V
2
+ V
1
) x (H
2
– H
1
) x ½(W
2
+ W
1
)
Path 3. Height H
3
Path 1 Height H
1
Path 2. Height H
2