Abstract: A self-contained unit has a probe (N) urgeable against a structure to be tested, a shock assembly (H, I, J, F, M) for applying a shock to the structure through the probe (N), and a transducer (A, B, C) for receiving resulting vibrations from the structure through the probe (N) and providing electrical output data. The unit also includes a memory (b) for storing the data. The unit has a tubular body (E) in which the transducer (A, B, C) is receivable. The transducer (A, B, C) is linked to a weight (H) and springs (G, I) such that urging the probe (N) against a structure progressively compresses springs (G, I), drives the enclosure (A, B, C) into the body (E) and raises the weight (H) until the weight is suddenly released and hits the transducer (C) to supply the shock.

Abstract: Apparatus for locating or monitoring the condition of an inaccessible conductor comprises an antenna for receiving electrical signals due to an alternating current in the conductor. The antenna comprises at least two transducer assemblies each comprising two horizontal, preferably mutually perpendicular, transducers (preferably ferrite-cored coils). The signals induced in the transudcers can be processed to give information about the current in the conductor (indicative of its condition) or its depth, independently of the antenna orientation. Use of more assemblies can give better sensitivity. Assemblies including a vertical transducer can avoid the need for the antenna to be over the conductor.

Abstract: Apparatus for detecting underground conductors carrying AC, such as cables or pipelines, has two receiver coils with horizontal axes one above the other, and other coils. By making phase comparisons from a selection of these the apparatus is located directly above the conductor. Then using the two horizontal coils there is derived a signal corresponding to the depth of the conductor, which can be visually indicated. Also, this depth signal, which is continuously available as the conductor is followed, is used to modify an output from one of the coils so that as the depth varies that output remains constant provided there are no discontinuities or faults in the cable.