Quote: (Originally Posted by
Rebreathing Red)
I have nothing to gain or loss in this. I'm just sharing what I know.
So let's ignore my prevoius graph and do a little math.
A straight line can be defined by the equation y=mx+b
So if po2 0.0 = 0 millivolts and sensor A has the following po2 0.21 = 12 mv (newer sensor)
Sensor B p02 0.21 = 9 mv (older sensor)
since po2 0=0 then b=0 (no linear offset)
therefore y=mx
A
13=0.21m
m= 61.905
B
9=0.21m
m=42.857
The slope is different on sensor A and B
so looking at a po2 of 1.6 we get the following
Sensor A =61.905*1.6 = 99.048 mv
sensor B = 42.857*1.6= 68.571 mv
you can make your own conclusions
Red,
What you wrote is right on. Cells will exhibit somewhat different response slopes, as you showed. That's why each (panel meter, microcontroller, whatever) needs to be calibrated to a particular sensor. If one were to switch one PO2 indicator between different cells, the readings certainly wouldn't be the same. The adjustment pot simply adjusts the gain or slope of the PO2 indicator to the slope of the sensor. The two response "curves" you illustrate are perfectly suited for a single-point calibration, since they are essentially straight lines in the area of interest and have a Y-intercept of zero. Just sharing what I know.
-Dan