Fibre Mux Pod
The SDC installed Fibre Multiplexer Pod is the heart of the iBIS.
This 1-atmosphere pressure vessel contains the distributed processing and electrical interfaces for all SDC electrical equipment. The pod is installed vertically on the SDC with a number of electrical underwater connectors mating to the interface end-cap.
The Mux pod is rated to 600MSW depth, and is manufactured from 316 stainless steel. Inside the pod there is a card-rack and backplane that holds a variety of interface circuit boards for the different electrical functions on the SDC. This pod also houses the two fibre-optic multiplexer units.
The SDC Multiplexer pod operates from a 25V DC input supply, and this is provided by two separate 25A supplies fed from the two AC Power Pods on the SDC. By keeping the AC power supplies inside the AC pods, the Mux pod only has low-voltages inside.
The two 25V input supplies are combined into a common 24V DC ‘bus’ by the use of a network of diodes. This allows the system to operate with only one of the two AC Power Pods functioning – but to share the power supply loading when both AC pods are available.
The internal circuit functions in the Mux pod include the following:
- 32 x fault-protected switchable 24V DC outputs used to operate 24V DC SDC mounted equipment;
- 2 x isolated diver hat-camera power supplies;
- 4-channel diver voice comms interfaces (microphones and headphones for divers, and microphone & speaker for the bell);
- 2 x fibre-optic multiplexer units, each with 4 video uplink, 4 bi-directional RS232, 4 voice comms channels and 1 Ethernet channel;
- Fibre-optic interface PCB with MP3 test audio system;
The SDC Mux pod uses a dual microprocessor system to provide high levels of redundancy. These dual processors operate as a duty / hot-standby pair, and each is capable of operating the complete SDC system. All interface circuits inside the Mux pod communicate with the dual processors over a redundant serial bus.
In the event of an emergency rescue of the SDC, the Mux pod allows a connection of a Life Support Package (LSP) to an emergency stab-plate system. This connection provides 24V DC power for the operation of two CO2 scrubbers and two bell internal lights inside the SDC. Power to these emergency services is routed via a relay connection system inside the SDC Mux pod.
The Mux pod incorporates a sophisticated diagnostics system, including detectors for water ingress, internal temperature sensors and a vacuum seal-checking system. The vacuum system uses a non-return valve on the pod end-cap allowing a partial vacuum to be ‘pulled’ prior to diving the SDC. This vacuum ‘sets’ the sealing ‘o’-rings correctly and by means of two internal vacuum sensors, allows technicians to check the pod seal integrity prior to diving.