Though of course it is not visible, the software is a very important part of the CCR Liberty.
The software’s main task is regulation of the partial pressure of oxygen in the breathing loop. According to the data from the oxygen sensor, it opens the solenoids, by which oxygen is added to the breathing loop in order to maintain the required partial pressure of oxygen (setpoint). Besides that, it is also able to use data from the depth sensors. If, for example, the diver is descending or ascending, regulation of the partial pressure of oxygen under the influence of dead time is generally more difficult and less precise. Thanks to the data from the depth sensors, the regulator can approximately predict which data the oxygen sensors will show in several seconds and thus limit overshoot which a regulation system without a predictive element would necessarily allow.
In the event of an extensive malfunction, e.g. flooding of all oxygen sensors, the ppO₂ regulation system is able to switch to indirect measuring using the helium concentration sensors. However, in order for this to be possible, a diluent containing helium must be used.
The CCR Liberty can be switched to several operating modes.
The apparatus is switched to standby mode with the “switch off” command, in which case it is not actually switched off. Every five seconds it momentarily switches on the depth sensors and determines whether or not the apparatus is in the water. If so, it is immediately activated and switches to dive mode. This functionality is intended not only for absentminded divers, but can also be useful in other situations, as described in the chapter The final decision is up to you.
After being switched on, the apparatus switches to surface mode, in which it is possible to calibrate the sensors and to set various decompression parameters, properties of the apparatus, and mixture compositions.
The basic operating mode is the CCR (dive) mode. The solenoids start to supply oxygen; decompression is calculated; and the handsets display depth, dive time, setpoint, partial pressure of oxygen and other necessary information.
If necessary, you can switch to Manual CCR mode, which functions in the same manner as CCR but shuts down automatic oxygen regulation. In this mode, it is expected that you will add oxygen yourself using the manual bypass valve. This mode is intended for resolving possible problems in the regulation of oxygen supply, though some divers prefer to use it instead of automatic oxygen supply in small depths.
The open-circuit mode is intended for handling a truly serious malfunction. The apparatus ceases to function as a rebreather and essentially becomes only a somewhat larger dive computer. It is assumed that at the moment you start using this functionality, you are no longer breathing from the CCR Liberty, but from the open-circuit bailout apparatus. This results in an adjustment of the decompression calculation, which switches to a predetermined breathing mixture (which of course you can change during the dive).