or more turns around the circumference of the pipe section 12 in a manner that allows the length of the optical fiber within the coil 32 to change in response to a change in the circumference of the pipe 12 if for example a pipe 12 can be expected to see a maximum circumferential change of u201c y u201d then a one turn coil will be subject to a maximum potential change in length of u201c y u201d or some known function of u201c y u201d if an optical measurement technique is not sensitive enough to register a change in distance equal to u201c y u201d then the coil 32 can be wrapped to include u201c n u201d number of turns the change in fiber length u201c y u201d per turn is therefore multiplied by u201c n u201d turns and a change in fiber length great enough to produce a useful signal i e u201c n u00b7 y u201d is provided in fact the same technique can be used to not only provide a minimum useful signal but also to increase the sensitivity of the sensor 32 and therefore the range of detectable changes in the circumference of the pipe 12 in all cases the length of the optical fiber in each coil 32 is known and is chosen to produce the sensitivity required to sense the disturbance s of interest for that particular sensor the preferred embodiment as described above includes coils 32 wrapped.