Thermo Scientific HB-S200, User Manual

Page: 14 / 77

Sarasota 200 Ultrasonic Multipath
Flowmeter
Section 1 INTRODUCTION Page 1-4 Thermo Fisher Scientific
INTRODUCTION
1.2.5.1 Mid section method
In the mid section method, the slice boundaries are defined by lines mid way between the
paths. The slice velocity is taken as that determined by the ultrasonic path within the slice and
the slice area as the product of the slice height and the (average) width. The upper boundary
of the top slice is the water surface. At the bottom, an additional slice is defined between the
bed and a line half way between the bed and the bottom path. This bottom slice has a
weighting factor, K, normally between 0.4 and 0.8 to allow for the slow moving water near the
bed. To reduce the uncertainty of this factor, the bottom path should be positioned as close to
the bed as practical.
Illustration of the mid section method for 4 paths
Height H
S
Path 4 Height H
4
Water Surface
Width W
4
Bed Height H
0
Bottom panel
Top panel
½(H
4
+ H
3
)
Width W
3
Width W
2
Width W
1
Width W
Bed
Path 3 Height H
3
Path 2 Height H
2
Path 1 Height H
1
Height H
0
½(H
3
+ H
2
)
½(H
2
+ H
1
)
½(H
1
+ H
0
)
Q
S
= ½V
3
(H
4
– H
2
)W
3
Q
S
= ½V
2
(H
3
– H
1
)W
2
Q
S
= ½V
1
(H
2
– H
0
)W
1
Q
S
= ½kV
1
(H
1
– H
0
)W
Bed
Q
S
= V
4
{H
S
−
½(H
4
+ H
3
)}W
4