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Alex, in the Biomarine 155 there are three oxygen sensors. All this
information comes from a manual that Biomarine supplied with the unit. 

Their sensor is made up of a lead anode, a gold cathode, a teflon
diffusing barrier, a KOH electrolyte bath, and an external load resistor.
The gold cathode is the reaction site for the reduction of oxygen
molecules into hydroxyl ions; gold is not consummed in the reaction. The
hydroxyl ions react with the lead electrode, forming lead oxide and
releasing electrons. Electron flow between anode and cathode is through an
external resistor, producing an output voltage. Output voltage is a
function of the number of oxygen molecules reduced at the gold electrode.
Sensor output is 18-21mv in air at 1 atm; 1 atm pure O2 would read 50-99
mv. The unit's primary display (worn on right hand) has a pO2 section that
has five illuminated sequential letters and numbers to indicate normal,
high or low levels of oxygen according to the calibration. The unit can be
calibrated from 0.7 to 1.3 pO2. The unit's secondary gauge (clipped to D 
ring on BC) is an analog meter (digital in MK16) which displays sensor 
output and battery voltage. Individual sensor readouts are obtained by 
turning a knob to sensor 1, 2, 3 dial position. Each sensor generates 
sufficient electrical output to activate the meter and does not require 
electronic amplification. Is this what you mean by, "how are they read"? 
If not, then the quick answer is, I read them with my eyes. I can do this 
in the dark because the secondary gauge has a tritium face that 
glows in the dark (inset so that no glow escapes; with a velcro'd lid). Rod 

On Tue, 26 Mar 1996, Alex Varouxis wrote:

> How many PO2 sensors are used in a rebreather and how are they read?
> 
> -Alex
> 
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