The UCPH borehole logger

The University of Copenhagen (UCPH) logger measures borehole inclination, azimuth, temperature, diameter and pressure. Readings are made continuously by the logger, and the results are transmitted every 3s to the surface. The tool remembers the maxima and minima of the diameters measured in each 3-s period. Thus, all extremes in diameter are recorded. The calliper is designed to give a resolution of 0.1mm. A trade-off of this high resolution is that the tool cannot penetrate in a hole inclined more than 15^o, and that the hole wall must be reasonably smooth in order to avoid hanging the tool on its callipers. The logger uses a single conductor coaxial steel cable, 3.1mm in diameter. The winch has a standard 3-phase AC motor, which is powered by a variable frequency drive. The weight of the winch, including 3km of cable, is 400kg, and the total power consumption is less than 2kW. This makes it possible to deploy the logger with light aircraft (Twin Otter or helicopter) support.