The beam position system of the CERN neutrino to Gran Sasso proton beam line

The CERN Neutrinoto Gran Sasso(CNGS) experiment uses 400GeV protons extracted from the SPS, which travel along 825 meters of beam line before reaching the CNGS target. This beam line is equipped with 23 BPMs capable of measuring both the horizontal and vertical position of the beam. The final BPM is linked to the target station and due to radiation constraints has been designed to work in air. This contribution will give an overview of the BPMs used in the transfer line. It will also provide a detailed explanation of their logarithmic amplifier based acquisition electronics, which consists of an autotriggered sequencer controlling an integrator, the A/D conversion and the Manchester encoded transmission of the digital datato the surface. At the surface the digital datais acquired using the Digital Acquisition Board (DAB) developed by TRIUMF (Canada) for the LHC BPM system. Results from both laboratory measurements and beam measurements during the 2006 CNGS run will also be presented.