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BS3680 Thin Plate Weirs
Point of Measurement
The transducer must be above the maximum head P704 by at least the near
blanking distance P107.
For Rectangular and V-notch weirs, the head is measured at a point 4 to 5
times the maximum head upstream from the weir plate, to ensure the
surface of the liquid is not affected by turbulence or drawdown.
(See DRWG 8)
Calculations
BS 3680 Rectangular Weir
ABSOLUTE
If the flow calculation is to be absolute P702 = 1 the flow will be calculated
using the formula: q = C
e
2/3(2gn)
0.5
b
e
h
e
1.5
Where: q = flowrate
Ce = discharge coefficient calculated by Flow 3 P723
gn = gravitational acceleration (nominal value = 980.66 cm/s
2
)
be =effective approach width where b is approach width
(Dim “A”) P710
he = effective head
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