BODC HEADED DOCUMENT NO. 32414 Applies to BODC Series Ref. Nos.: 36734, 36746, 36758, 36771, 36802, 36814, 36875, 36887, 36899, 36906, 36931, 36943, 36979, 36980, 36992, 41195, 41202, 41287, 41299, 41306, 41367, 41379, 41460, 41472, 41484, 41496, 41503, 41515, 41527, 41552, 41564, 41576, 47326, 47338, 47363, 47375, 47399, 47406 I.O.S. Mk IV Pressure Recorder This instrument was developed at I.O.S. Bidston and is a deep water pressure recorder (i.e. used at depths between 300m and 5000m). Each recorder consists of one or two Bell and Howell strain gauges and/or a Digiquartz pressure sensor and a temperature sensor. The sensors are interfaced into a Seadata cassette recording system. Sampling is usually every 3.75 minutes with the integration period equal to the sampling interval, but may be set to other sampling intervals. For example with a 3 second sampling interval and integration period the instrument may be used as a wave recorder. The recorder is housed in a tubular aluminium frame 1.3m in diameter by 1.4m in height attached to a disposable steel ballast weight. The data logger together with the associated battery supply is lowered into a central 15cm (internal diameter) aluminium tube. Sensors are mounted externally with Marsh Marine connectors. The assembly free falls to the sea floor. An acoustic release system is used to separate the ballast weight and buoyancy is provided by Corning glass spheres attached to the aluminium frame.