Bill, Peter, thanks for the suggestions.

Although I think the self-calibration idea is ingenious, in my app. it might be difficult/cumbersome to implement, as I have 4 channels, and when I deploy the instrument it might not be possible to sweep each channel from minima to maxima at the same time.

Also, I notice that the dissimilar readings on the different channels are happenning not because of the sensors (caps) themselves, but the inherent differences in the pic pins, even if they are on the same port.

I got around this by a technique that seems to be working very well; maybe it would helps others with a similar issue.

I am using just 1 pin to measure all 4 channels; the 4 sensors are multiplexed using a 4066 CMOS switch chip.

The outcome is that I now need to calibrate for just one channel, and as long as my sensors are uniform (which I found they are) I get a consistent reading for all 4 of them as I scan them one after the other.

Regards,

Anand