Prism Topaz
Posted By Grant Graves on 5 September 2003
The Topaz controls oxygen set point via a digital computer controller with
a true voting system for the three onboard oxygen sensors. The electronics
are fully potted. The digital electronics allow for simple push button
calibration. There are five pre-selected set points (0.7, 1.0, 1.2, 1.3,
1.4 ATA oxygen) available to the diver. Electronics and unit status is
displayed via a heads down LED display that mounts at lower eye level on the
mouthpiece ring.
The heads down display allows for hands free continuous unit status to be
read at a glance. 
The display incorporates set point status with high alarm, low alarm and at
set point lights. Alarm displays included sensor, battery and oxygen status
alarms. All electronic and solenoid operations are fed by a 9 volt
battery. Typical operation time on a single battery is over forty hours.
The oxygen solenoid is outside of the breathing loop. A simple on/off
switch allows the user to turn the unit off or on as desired at any time.
One of the unique features on the Topaz is a true secondary display. This
display is easy to read and allows the diver to check each sensor’s status
totally independent of any electronics or battery. The secondary displays
oxygen partial pressure levels for each sensor driven solely from the
voltage outputted by the sensor itself. This allows the Topaz to be
operated easily with the electronics turned off and/or no power available to
the unit. In fact, electronics failure or loss of battery power is not a
bailout situation with the Topaz because of this feature. The secondary
also displays battery voltage and unit set point.
The Topaz easily adapts to various cylinders sizes, allows for use of a cover for increased hydrodynamics or flies equally well without it. The unit has off board diluent bailout built-in. Of course, the unit is bubble less unless the diver is ascending and provides release of expanding gas on ascent with a standard over pressure relief valve. However, most users simply exhale out of their nose for more intimate control of the process.
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