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Example 3 BS3680 Rectangular Weir  
 
 
 
In  this  example,  it  is  required  to  calculate  to  the  flow  through a  BS3680 
Rectangular  weir.  Absolute  calculation  will  be  used,  and  there  is  a 
requirement for an alarm to indicate a high flow condition to be set to relay 
3. The flow rate is required to be displayed in US gallons/minute and the 
totaliser  is  to  record  the flow in  thousands  of  US gallons,  the  resettable 
totaliser is to be displayed during RUN.  
The distance from the end of the transducer horn (dB Mach 3) to zero flow 
(P105)  is  40  inches  and  max  head  (P704)  is  16  inches,  maximum flow 
(P705) which will be calculated by the Ultra unit as 2385.63 USG/Min. 
Approach width (Dim “A”) P710 = 18 inches          
Crest width (Dim “B”) P711  = 12 inches          
Crest Height (Dim “C”) P712   = 10 inches