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BS3680 Rectangular Broad Crested Weir
Point of Measurement
The transducer must be above the maximum head P704 by at least the near
blanking distance P107.
The head is measured at a point 3 to 4 times the maximum head upstream
from the weir crest, to ensure the surface of the liquid is not affected by
turbulence or drawdown.
Calculations
ABSOLUTE
If the flow calculation is to be absolute P702 = 1 the flow will be calculated
using the formula: q = (2/3)
1.5
C
e
b(gh
3
)
0.5
Where: q = flowrate
Ce = discharge coefficient calculated by the Flow 5 P723
b = approach width P710
g = gravitational acceleration (nominal value = 980.66 cm/s
2
)
h = head
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