Page 83 
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 application is to be assigned to Point (transducer) 1. 
The distance from the end of the transducer horn (dB Mach 3) to zero flow 
(P1-105) is 40 inches and max head (P1-704) is 16 inches, maximum flow 
(P1-705) will be calculated by the Ultra Twin as 2385.63 USG/min.  
Approach width (Dim”A”) P1-710 = 18.0 inches  
Crest width (Dim “B”) P1-711     = 12.0 inches  
Crest Height (Dim “C”) P1-712      = 10.0 inches