Monitoring instrument

An apparatus in the form of a monitoring instrument for monitoring ionizing radiation comprising a water-proof housing assembly comprising a housing and a display panel, and incorporating an enclosure containing electrical apparatus, the electrical apparatus being housed within said enclosure and the electrical apparatus comprising a radiation detector for monitoring ionizing radiation, a power source for said radiation detector, and a data processor/controller, wherein said display panel is formed from a clear material encapsulating a visual display, said visual display displays at least one status or measurement related to ionizing radiation which is monitored by the monitoring instrument,

• wherein said apparatus is adapted for monitoring the proximity of a pipeline pig, said radiation detector is capable of detecting radiation emitted by a source of ionising radiation mounted on the pipeline pig, and said data processor determines the proximity of the pipeline pig from the radiation detected by the detector.