An inline optoelectronic converter configured to convert electrical signals to optical signals and to convert optical signals to electrical signals. The sensors attach to a downhole apparatus at a distance from one another. The inner bag is formed with an arcuate edge at the open end of the bag to inhibit formation of fissures in the outer membrane in this edge region. An orthogonal projection ) is applied to the composite of all signals for thereby projecting y onto the detection subspace.