An Electronic Mariotte Burette for Precision Controlled Water Pressures.

Measurements of soil hydraulic properties in the laboratory and field often require controlled water pressures and/or regulated water levels. The traditional way of controlling such pressures is by using a Mariottle bottle. A drawback of Mariotte bottles is that the pressures and/or pressure range is limited to the physical size of the actual burette used. In addition, the pressures at the outlet fluctuate slightly with the air bubbles that enter the system. Mariotte bottles further need some operator attention, because the water level inside the burette must be read to determine a flux rate (although this can be automated with pressure transducers) and because empty bottles must be filled “by hand”. In this poster we present a design that avoids most of these drawbacks. The new method uses small valves connected to low-quality vacuum and pressure to regulate the internal Mariotte pressure over a large range with an error of 0.5 mm pressure. The method is completely computer controlled and needs no operator attention. The poster will provide some practical examples.