Hi Wayne-
In regards to the screen going blank, this is not a properly functioning unit and should be returned to TUSA for evaluation. Please contact customer service at 800-482-2282 or
info@tusa.com to request an RMA#.
The F settings control the Gas 1 and Gas 2 percentages, the FO2 default 50 feature is explained in a bit more detail on page 42 of the IQ-900 user manual. The text is also here below:
When the FO2 50% Default is set On and FO2 Gas 1 is set for a numerical value, 10 minutes on the surface after that dive, the FO2 for Gas 1 will be displayed as 50 and further dives will be calculated based on 50% O2 for oxygen calculations and 21% O2 for Nitrogen calculations (79% Nitrogen) unless the FO2 for Gas 1 is set before the dive.
FO2 for Gas 1 continues to reset to the FO2 50% Default after subsequent repetitive dives until 24 hours elapse after the last dive, or the FO2 50% Default is turned Off.
When the FO2 50% Default is set Off, the FO2 for Gas 1 will remain at the last Set Point for the remainder of that series of repetitive dives.
The default FO2 for Gas 1 each new dive period is AIR.
When FO2 for Gas 1 is set for AIR, the calculations are the same as when it is set to an FO2 of 21%. When FO2 for Gas 1 is set to AIR, it remains set for AIR until it is set for a numerical FO2 value (21 to 50%).
When FO2 is set only to AIR, the O2BG and PO2 values and/or warnings will not be displayed during the dive.
MODs affected by the PO2 limit set will not be displayed when FO2 for Gas 1 is set to AIR.
Internally, the ZEN keeps track of O2 so that if FO2 for Gas 1 is subsequently set for a numerical value, the O2 accumulated during previous AIR dives will be accounted for in the next Nitrox dive (during that dive period and series of repetitive dives).
Once FO2 Gas 1 is set for a numerical value (21 to 50%) and a dive is made, the AIR option is disabled until 24 hours elapse after the last dive. The AIR option will not be displayed in Set FO2 Gas 1 until a full 24 hour Surface Interval has elapsed.
If FO2 for Gas 1 is set for 21%, it will remain set for 21% for that series of dives until set for a higher numerical value.
If the FO2 50% Default is set OFF, FO2 for Gas 2 will remain at it's Set Point previously selected until it is changed. If the FO2 50% Default is set ON, FO2 for Gas 2 will Default to 50% after the dive.
The ZEN is programmed to prevent FO2 for Gas 2 from being set at values lower than the FO2 Set Point for Gas 1. Gas 2 can only be set to values equal to or higher than the FO2 Set Points of Gas 1.
When setting FO2 for Gas 2, the lowest values available will be the Set Point of Gas 1. If FO2 Gas 1 is set for 32%, FO2 Gas 2 can only be set at values from 32 to 100%.
