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John wrote:

>The sensor's output will drop with time so I assume you meant (or
>want) an *adjustable* resistor in the ICL7106's support circuitry
>in order to be able to calibrate the module to display % O2 directly.

You're bang on there!  Conveniently the meter already comes with a 
potentiometer for adjusting the reference voltage.  This meter is calibrated 
and the pot then glued into place at the factory.  The pot doesn't have 
enough swing to allow calibration in PO2.  By changing one of the resistors 
you can move the calibration into a range where the pot can be used to 
calibrate in ATA of PO2. 

>With 200mV max readout that should give you a direct O2 readout down
>to a ppO2 of 2 atm :-).  Did you try the Mini-ox hyperbarically?

Yup, worked fine.  Bill cycled it down to 8-9 ATA many times in the pot and 
we've also had many, many dives in the 3-5 ATA range using the sensor.  We've
also given it temperature and humidity tests.  

Barrie

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