Control system

The CCR Liberty is controlled by two interlinked computers, designated as CUs in the schematic. Each computer has its own battery, two oxygen sensors, a pair of depth and atmospheric pressure sensors, and a helium concentration sensor. Each CU controls a separate electromagnetic valve (solenoid) for adding oxygen to the breathing loop and several other sensors that that are not shown in the schematic, such as a sensor for gauging the air temperature in the breathing loop.

Control system

If everything is operating normally, the computers mutually share data from the sensors (thus each of the computers has access to data from all four oxygen sensors), agree on which of them will open its respective solenoid if it is necessary to add oxygen (under normal conditions, the left and right solenoids alternate) and mutually synchronize all performed operations, such as decompression calculation. In the event that one of the computers fails, the remaining one has available all necessary devices (oxygen and helium sensors, solenoid) and information (decompression model status) for problem-free continuation of the dive and the diver’s return to the surface.

Two display units – handsets (HS) in the schematic – a head-up display and buddy display are connected to each control unit.

The handsets are designed a little differently than is common in the field. In the schematic, it is clear that they do not have their own power supply, as they are powered together with their respective CUs from the batteries housed in the warm breathing loop in the head of the apparatus, so loss of battery capacity in frigid water is not an issue. The control units can shut down power to the handsets in the event of a malfunction or short (e.g. in the case of cable damage).

The handsets do not control the solenoids, nor do they perform decompression calculations. They serve only as the terminal devices of the control units. For example, on the left handset press and momentarily hold the upper key, which is the command for switching to the high setpoint (predefined setpoints, designated as “low” and “high”, are available in the CCR Liberty). The handset sends the command to the left CU, which then sends it to the right CU. Both CUs now start regulation of oxygen at the level of the newly selected setpoint. Concurrently, each CU sends to its respective handset a command to display the new setpoint value. The diver who pressed the key on the left HS can thus see how the displayed setpoint value changed on both the left and right handsets.

The handsets have several sensors that are not shown in the schematic. The position sensor is used when setting parameters on the surface. The temperature sensor provides to the control unit data on water temperature; the ambient light sensor provides information for automatic control of the display’s brightness.

The head-up display (HUD) has three tri-color LEDs and is attached to the DSV in the diver’s field of vision. Blinking LEDs indicate the measured partial pressure of oxygen in the breathing loop as well as danger or malfunctions.

The buddy display (BD) on the head of the apparatus notifies the diver’s partner or instructor of critically dangerous levels of the partial pressure of oxygen.

The positioning of the HUD and BD are configurable so that you can exchange them or, for example, install two HUDs at the same time.

See also Fault-tolerant rebreather, Air-mass treatment and Handsets and pressure gauges

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