Oxygen sensor calibration should be confirmed prior to every dive and recalibrated as needed. Begin by disconnecting the counterlungs from the scrubber canister. Next insert the supplied calibration caps by pressing them into the fittings on the electronics head and end cap. The cap with the mushroom exhaust valve should be inserted into the electronics head fitting, and the cap with the BC fitting inserted into the end cap fitting.
With the oxygen cylinder valve turned off, disconnect the oxygen hose from the “y” block and connect it to the calibration cap.
Turn on the Petrel 3 controller and HUD.
While watching the PPO2 values on the controller and HUD, turn on the oxygen cylinder valve in short bursts a couple of seconds apart. The PPO2 values on all sensors should climb as oxygen is added.
Continue adding oxygen until all sensor values stabilize and do not continue to increase.
Once all values have stabilized at their maximum value, perform the calibration. See the Shearwater Petrel Dive CAN Rebreather Controller Model Operations Manual and the Shearwater HUD User Manual respectively for specific calibration instructions.
It is recommended to calibrate using 100% 02 if available, however it is possible to calibrate the controller using as low as 70% 02 if that is all that is available. If using a calibration gas less than 100% O2, the calibration FO2 setting will need to be adjusted in the controller first. See the Shearwater Petrel Dive CAN Rebreather Controller Model Operations Manual for more information on this.