It allows the calculation of the flow by measuring the level of he canals generating the Venturi principle.
Venturi measures are performed in canals with special shapes. In this type of canals, the level and flow have an exponential relation.
The normalized canals are those that have a normalized shape and dimensions where the relation between the water level in a specific point and the circulating flow is known.
The most common devices correspond to ultrasonic levels situated in some height over the level of the canal level, however, we have devices with hydrostatic measure that eliminate all errors due to foam and suspension solids when the water is not fully clean.
SENSOTEC has ultrasonic devices like the DINEL FCU-400 or the LEVELTEC MQ99 that incorporate a formulation of normalized canals in its programming in order to obtain a direct reading of the flow depending on the average level.
The most common levels are the Pashall y el vertedero.
Parshall canal
This one can be considered as a variation of the Venturi canal as it also experiment a lateral contraction followed by a throat with profundización de su solera and a subsequent divergence section.
They are prefabricated canals, with normalized measures according to ISO 9826:1992 that correspond with measures 1″ to 50”’ being the most usual measures up to 8′ with flows going to 1.100 l/s.
Vertederos
Based in the level disturbance caused when installing a vertedero in a final section. The vertedero is just an obstruction with opening calculated to cause the increase of level. The most common vertederos are called “V-Notch” as they have a V shape normalized from rules like ISO 1438/1-1980(E), ASTM D5242 andUSBR (1997).