Thomson weir

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Overflow of a Thomson weir with a triangular incision through which water flows out

A Thomson weir is a measuring weir for measuring the flow of water in a channel . It is a small weir with a sharp-edged sheet metal on the water side with a triangular incision with the tip pointing downwards, over which the water flows in the form of an overflow (hence also "triangular weir "). From the height of the dammed water level, one can deduce the amount of draining water with great accuracy, provided that the parameters applicable to the installation are observed. For the conversion of the water level in the flow rate, there are approximation formulas, in addition to the depth of water as a parameter and the discharge coefficient (after Poleni included) and the opening angle of the triangle. The water level can be measured with ultrasound, for example.

The triangular shape means that even small amounts of water can be measured, whereby errors of less than 5% can be achieved with correct installation. The triangular overflow cross-section is characteristic of the Thomson Weir; there are also measuring weirs with a rectangular attack ( roe buck weir according to Theodor Rehbock , Poncelet weir according to Jean-Victor Poncelet ) or other shapes.

Inventor and namesake was the Irish-Scottish scientist, engineer and inventor James Thomson (1822-1892). He was the older brother of Lord Kelvin .

Literature and references

  1. Thomas, CW (1959): Errors in Measurement of Irrigation Water. - Trans. American Society of Civil Engineers, 124: 319-332, 6 fig., 4 tab .; Reston.

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