Hi Again...
So tmd3, I must thank you very much for all your insight--I greatly appreciate it. With RC filters in the signal lines as you described, I see a dramatic improvement in stability of readings when the fluorescent light is on. I got rid of the power rail RC filter and I added a 0.1uF cap on the voltage divider for fc = 1 / 2(pi)(10,000)(0.1x10-6) = 159 Hz, and a 100 ohm resistor and a 10uF cap on the output of the differential amp for fc = 1 / 2(pi)(100)(10x10-6) = 159 Hz.
I had initially thought I'd use a 1k resistor on that diff amp output until I got to thinking that I really would prefer to minimize voltage drop so as not to have to compensate my current readings which are calculated from that voltage...so I dropped R down to 100 and went with a larger cap. My instincts tell me there is more to selecting that resistor than I am aware of now, but this seems to work so I think I will go with it and read up more for next time. I imagine that the current between that op amp and the ADC is minimal, so I could get away with a larger resistor (and smaller cap) and still not drop a very noticeable amount of voltage.
And winner10920, your point (and tmd3's earlier) about attempting to eliminate the noise at the source certainly sounds like the best design practice...and I will look into that. For now, I'm content to have learned a little about the practical application of simple RC filters!
Thanks again!
Mike
