Quote: (Originally Posted by
Dsix36)
I agree about the atmospheric pressure and the mv readings. The readings do not always drop, sometimes they raise.
It is about the amount of change in readings from one time to the next AND compared to the amount of change in the readings from the others cells also.
cell 1 changed by 2mv
cell 2 changed by 1mv
cell 3 changed by 6mv
Now is the time to begin suspecting cell 3 MAY be on the verge of failing.
The easier and more reliable way to tell is to observe where your PO2 reading falls to in air after you have done your oxygen cal (I'm assuming your system uses a 1-point calibration protocol). If it falls back to somewhere substantially above .21, then you a have a more positive indication of cell failure. I'll only elaborate further if requested.
The above mentioned 6mv change can be due to a ~1.2mV (6/4.8) change in the ambient mV of your cell, easily caused by dampness, or other.
mV readings are only of any use in 2-point cal systems. They are redundant in 1-point cal systems, and 1-point cal systems are a more simple and superior method of controller calibration, IMHO.