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www.sea-technology.com February 2016 / st 11 at abyssal depths. After that project, the development of the NEXUS multiplexers began in earnest in 1999 after having been suggested by the multibeam echosounder manufacturer Reson. NEXUS MK I In the late 1990s, there was a trend in the market for ROV pipeline surveys to replace the dual-head-scanning proflers with multibeam sonar systems in order to in- crease survey speed, data quality and accuracy. However, the multibeam sonar systems required transmission of a much higher amount of ROV sonar data, and with the long umbilicals this could only be done via fber-optic telem- etry. Together with sonar data the survey crew also typi- cally needed data sets from gyros, MRUs, sound velocity sensors, DVLs and depth sensors. Reson experienced that very often mobilization of their multibeam sonar systems on the ROVs was delayed because the interfacing of the typical two sonar heads plus the additional sen- sors was a bigger task than expected. Based on the experience from the Geostar project, the NEXUS MK I system was developed to make this task much easier. It just required one extra fber in the ROV umbilical and 110 to 240 VAC power supply to the NEXUS sub- sea electronics bottle and harness cables to be connected between the NEXUS bottle and the different sensors and sonar heads. A fber-optic cable connection between the bottle and the umbilical J-box was also required to make the data available topside on the rear side of a 19-in. rack mount unit. The system was a fully transparent data telemetry system, with delay only equivalent to the minor delay in the fber. NEXUS MK II The NEXUS MK II was a drawing board model only and never came into production. It would have been a multiplexer system only controlling two sonar heads and transmitting their data to the surface. NEXUS MK III Developed in the year 2000, the NEXUS MK III is very simple and com- prises a dual (P)ECL board or two GbE boards to be connected in the ROV electronics pod. Topside, a similar set of boards are delivered in a 19-in. rack mount unit. If the sonar heads require separate RS232/485 control, this must be handled via the existing ROV mul- tiplexer. NEXUS MK X In 2001, the bigger NEXUS MK X was developed. This system comprised a much bigger electronics bottle and a topside with room for the Focal 903 type multiplexer. Remote and console 903 boards were Eurocard size, hence the requirement for a larger ID of the electronics bottle. The interface of video cam- eras was also included, with eight video channels, up to 32 serial, plus the (P)ECL and Ethernet signals. The fange of the pressure vessel could not accommodate the large number of connectors. Therefore, two oil-compensated J-boxes were connected with the electronics bottle via multipin connectors. The individual sensors and cameras could then connect their harness cable to the dedicated connector on the J-box. A couple of the NEXUS MK X systems were also ftted with a small touch screen topside for camera and pan/ tilt control. The biggest customer was Thales Geosolutions (Top to Bottom) The MK E allowed the Spanish Institute of Oceanogra- phy (IEO) to transmit data and vid- eo through the existing coax cable mounted on the vessel's launch and recovery system. NEXUS MK VI sys- tems are used on several deep-tow sonar systems during SAR operations, including that for Malaysian Airlines MH370. NEXUS MK C on MILET toolsled supporting a USBL-navigated video and SLR camera platform for benthic surveys, with effec- tive operating depths of 2,500 m. IKM Subsea Merlin work-class ROV provided with NEXUS MK C multiplexers comprising com- plete topside units installed into 19-in. rack boxes with diagnos- tics on both LED levels and an extensive GUI for systems health data, a TMS stack, and an ROV stack. (Photo Credit: IEO) (Photo Credit: IKM)