Introduction to Cables
Many different types of cables are installed for different purposes at ONC. Submarine cables are designed to handle the harsh conditions of the ocean environment. Typically, temperatures are cold at depth, pressure increases and strong currents and wave action can occur in many coastal locations. Human activities such as fishing and hazardous geological features such as hydrothermal vent fields must also be considered when building, laying and burying cables. At Folger Deep, for example, a heavily armored cable with protective wire sheaths is deployed to protect against abrasion from waves and current action.
ONC uses fiber optic cables for high speed data communication. Fiber optic cables allow data to from instruments to be transmitted to shore in near-real time over long distances using the speed of light. Hybrid cables are also commonly used, and include both optical fibers to carry information and electrical conductors to transmit power.
Backbone cables carry both power and fibre optic communications across the network. In the NEPTUNE Observatory, the backbone cable is a large loop. Data is passed in both directions along the loop to ensure a communication path if one section of the backbone cable is damaged or cut. The NEPTUNE backbone cable is approximately 800km long, VENUS Strait of Georgia is approximately 40km long and VENUS Saanich Inlet is 3km long. To prevent optical signals from degrading as information is passed along the backbone cable, repeaters are used at regular intervals. Also known as optical amplifiers, repeaters boost the optical signal to prevent data loss. Branching units on backbone cables distribute power and communications from the backbone to spur cables which connect to nodes, via optical couplers.
- Read about the long distance cable lays at Cascadia Basin
- Read blog post about cables in The Wire of Wiring the Abyss during the 2012 offshore expedition
Introduction to Connectors
ONC uses several types of connectors to connect instruments, junction boxes and nodes to cabled observatories. The type is connector is based on the type of instrument and must consider the frequency and logistics of deployment and recovery.
Electrical dry-mate connectors are types of connectors that must be connected in air, with the mating interfaces dry and sealed from the external environment. ONC typically only installs these type of connectors in a controlled environment at the testing facilities at the Marine Technology Centre (MTC). Underwater mateable connectors are types of connectors that can be connected underwater, with use of an ROV. They are constructed with features that protect the electrical and optical components from surrounding seawater. Underwater mateable connectors adds modularity to observatories, allowing individual instruments to be recovered and installed without disturbing instruments that are co-located on the seafloor. ONC typically uses these type of connectors on the NEPTUNE observatory where disturbing deep water instrument platforms is costly and time-consuming. Another type of connector commonly used as ONC is called a wet mate. These are connectors that are safely connected on the deck of a ship, on a dock or out in the elements during expeditions. They are nicknamed 'Splash Mate' connectors. While they are mated above water, they do not need the same controlled, dry and dust-free environment as dry mate type connectors.
Another option to connect instruments directly to cable assemblies are penetrators. Electrical penetrators are typically used on junction boxes and nodes and allow a cable assembly to penetrate a bulkhead or an instrument package without the use of any connectors.
Dust Caps and Parking Positions
In some cases, ports on junction boxes and nodes are not in use. ONC uses a special type of connectors called a 'Dust Cap' or 'Parking Position' to protect connectors from corrosion and exposure to seawater. Dust caps are a connector with no cable attached. Nicknamed 'Dummy Plugs', they are capped on unused ports by ROV, forming a seal. This allows the open port to be protected until it is used at a later time.
ONC also uses 'Parking Positions' to protect cables that have an unused connector end on the seafloor. If a cable end is left exposed, ONC uses a small frame called a parking position. The parking position is basically a portable connector panel that can be carried by an ROV and sits anywhere on the seafloor. It connects to the cable end, protecting it from surrounding seawater until it will be connected to an instrument, node or junction box.