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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 transducer to be used is a dB3. 
The  distance  from  the  face  of  the  transducer  to  zero  flow  (P105)  is  40 
inches and max head (P704) is 16 inches, maximum flow (P705) will be 
calculated by the FlowCERT LITE 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