"Long-term precise measurements ..."

Baumer hydrostatic sensors measure filling levels, water columns and surface levels. 
They recognize the differences in pressure, no matter what the fluid and environment, from 1 mH2O upwards.

Like the human ear they react highly sensitively to differences in pressure and pass these on to the controls as a linear scale. To do this, the pressure membrane is directly in contact with the fluid and - unlike other physical approaches to measurement of filling levels - is resistant to interference from external factors. The result is undistorted and stable measurements over the long term, even for difficult applications.