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>Posted on 30 Oct 1996 at 13:15:59 by Barrie Kovish
>
>>2) Has anyone done the calculations electronically, ie used an amplifier =
>>to boost the o/p. eg the 11.7mv reading given in the example to 21( =
>>20.9) mv
>>for air. ( Other than in a proper O2 meter of course.)
>
>I bought a ICL7106 based millivolt meter for about $25.00CDN.  There is one
>resistor on the board that needs to be replaced ($0.05CDN) and then the circuit
>can be calibrated in PO2.  The thermal stability of the circuit is fine but
>there is no temperature compensation for the sensor.  I calibrated in air and
>then checked pure O2 with about 4% error at 100%.  I was using a miniox sensor
>at the time.


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.

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?

Regards,
John

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