The v-notch allows to transform, in open channels, the value of the free surface of the water in an instantaneous flow measurement.
It can have various shapes depending on the range to be measured.
It can be made of a simple stainless steel sheet with sharp edge and the sides of the weir are the walls of the same channel (Bazin type), or consists of a stainless steel sheet with a rectangular or trapezoidal section (Cipolletti type) for water flow over 20 -30 l / sec, or consisting of a triangular section plate (30 to 45 ° angle, Thomson type) for water flow rates below 30 l /s circa.
The measurement of the free surface of the water can be made visually by using a hydrometric rod, or by an electric level or vibrating wire gauge placed inside the tank, or it can be measured using a ultrasound gage.
For reliable measurements, the following conditions must be verified:
- the canal upstream will have a fair slope (1-3%) and rectangular section for a length of at least 10L (where L=width of canal);
- the measuring point of the water head “H” will be at a minimum distance of about 4H from the weir;
- be sure the air under the water which floods immediately after the weir, will be in contact with the barometric pressure (do not create a closed chamber);
- the possibility of solid materials being drawn by the current and deposited upstream of the measuring equipment will be kept in mind. Accumulated sediments may affect the reliability of measurements, so that sediments should be cleared regularly.
- Material: stainless steel;
- Tickness: 3 mm;
- Triangular notch shape (various angles): 500 x 500 mm
- Rectangular notch shape: 600 x 500 mm