Abstract: The invention relates to an apparatus making it possible to measure the position of a moving bar in a non-magnetic guidance enclosure. The bar carries a permanent magnet, whose position is detected by at least one group of magnetometer transducers, arranged along a generatrix of the enclosure. The transducers of the same group are connected so as to form a matrix of n rows and p columns. The exciting windings of the transducers of the same row are connected in series and each row is supplied in turn by a multiplexing circuit. In the same way, the reading windings of the transducers of the same column are connected in parallel and each column is scanned in turn by a multiplexing circuit.