State Primary Standard of the Unit of Length for the Liquid Level

The state primary (national) standard of the unit of length for the liquid level (DETU 03-02-15) reproduces the unit of length using the world constant - the speed of light in vacuum. The transfer of the size of a unit of length to high-precision level meters is carried out by direct comparison.

The standard is built on the basis of a vertical cylindrical steel tank with water and a laser interferometer. Water supply and drainage is performed using an automatic damper.

At the top of the tank is a platform on which are fixed level gauges, verified or calibrated. The laser beam is reflected from optical reflectors, which are mounted on three floats. The floats move during the movement of the water surface when changing its level in the tank strictly vertically along the stretched cables. The depth of the floats in the event of a change in water temperature is taken into account in the electronic controller. To correct the refractive index of the atmosphere, the temperature and humidity of the air and atmospheric pressure are measured.

There are no other such standards with relevant metrological characteristics and range in the world.

Metrological characteristics


from 0 m to 20 m

Uncertainty by type A (uA)

0,10 mm

Uncertainty by type B (uB)

0,08 mm

Total standard uncertainty (uC)

0,15 mm

Extended uncertainty (U)

0,30 mm