Junction Boxes


Junction box LJ03A rests on the deck of the R/V Sikuliaq, fully tested and ready for installation at the base of Axial Seamount. Credit: M. Elend, University of Washington. V16.

To access specific RCA experimental sites, low- to medium-power, and low-voltage junction boxes (Secondary Nodes) are connected to the Primary Nodes by extension cables that can reach up to ~ 5 kilometers in length. All junction boxes were designed and built by the UW RCA Applied Physics Laboratory, which allows rapid refresh capabilities and significant maintenance efficiencies. Eighteen junction boxes are included on the RCA: all have been operating flawlessly since their installation in 2014.

Each junction box includes eight configurable sensor ports that can handle 12, 24, and 48 VDC, with communication capabilities of 10/100 Mbps Ethernet (4 wire), RS232 (Request to Send and Clear to Send available), and RS485 (full/half duplex). The source of all timing is redundant GPS based time servers in the Shore Station. For Ethernet connected instruments, Network Time Protocol provides ~10 ms accuracy and Precision Time Protocol (PTP IEEE-1588) provides sub-10 us accuracy. Pulse Per Second timing with Time of Day string (PPS, TOD) is available on all ports with ~10 µs accuracy achievable. For serial instruments without timekeeping capability, received packets are time stamped with ~10 ms accuracy.


A medium powered junction-box (MJ03B) in the ASHES hydrothermal field. The titanium cylinder inside the frame hosts the power converters, data ports, and communication capabilities to shore via the Primary Nodes.
MJ03B was installed as a ‘subnet’ during VISIONS’13 – two short-period seismometers are now connected to it via a 50 m and 1.2 km extension cable, respectively.  

Ports are configured predeployment to meet each instrument power and communication requirements. Each port can provide either 50 or 200 Watts, depending on the type of Secondary Node. Instrument extension cables are of variable length: RS232 instruments ~ 10 m, RS-422/485 instruments 500 m at 200 kbps to 1.2 km at 38.4 kbps, and Ethernet 10/100BASE-T instruments ~ 70 m. The cables are connected either through dry mate (MHDXL-12-FCR) or ROV wet-mate (ODI Nautilus 12-way) connectors. 375 VDC and 1 Gbps fiber optic Ethernet is provided via expansion ports, providing “daisy-chain” capabilities between Junction Boxes, making the system highly expandable.

Considerable effort was put into the design of the Secondary Nodes to make them robust in the event of faults within the system. Telemetry is collected for voltage and current consumption of each instrument as well as internal temperature, humidity and pressure of the junction box housing. Additionally, extensive Ground Fault Detection (GFD) circuitry is employed to discover inadvertent connections to seawater within the instrument or its associated cabling.

The RCA team works with interested researchers to understand required port configurations for PI instruments that are funded outside of OOI for installation on the cabled array. Significant expansion capabilities are available at each site.

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