Page 105
RATIOMETRIC
If the flow calculation is to be ratiometric P702 = 2 the flow will be
calculated using the formula: q= q
cal
C
e
/C
ecal
(h
e
/h
ecal
)
1.5
Where: q = flowrate
q
cal
= flowrate at maximum head P705
Ce = discharge coefficient calculated by Flow 3 P723
Ce
cal
= discharge coefficient at maximum head
he = effective head
he
cal
= effective head at maximum head
BS 3680 V-Notch Weir
ABSOLUTE
If the flow calculation is to be absolute P702 = 1 the flow will be calculated
using the formula: q = C
e
8/15tan(theta/2) (2gn)
0.5
h
2.5
Where: q = flowrate
Ce = discharge coefficient calculated by Flow 3 P723
theta = v-notch angle
gn = gravitational acceleration (nominal value = 980.66 cm/s
2
)
h = head
Flow 3 pre-sets the angle (theta) on selection of the chosen device this angle
is 90 degrees for a BS 3680 full 90 degree V notch weir, 53 degrees 8
minutes in the case of the BS3680 half 90 degree V notch weir and 28
degree 4 minutes in the case of the BS3680 quarter 90 degree V notch
weir.
RATIOMETRIC
If the flow calculation is to be ratiometric P702 = 2 the flow will be
calculated using the formula: q = q
cal
C
e
(h)/C
e
(h
cal
)(h/h
cal
)
2.5
Where: q = flowrate
q
cal
= flowrate at maximum head P705
Ce(h) = discharge coefficient for head
Ce(h
cal
) = discharge coefficient for maximum head
h = head
h
cal
= maximum head P704
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