Magnetometer Mixer

Each channel of my magnetometer (see yesterday's post) will pick up a trembling pin. I have built a "mixer" for these two channels, but now: should I wire the mixer as a summing amplifier or as a subtracting amplifier? 

• Add Channel 2 to Channel 1 = double the sensitivity, or
• Subtract Channel 2 from Channel 1 = nil sensitivity.

The advantage of the first option is that the magnetometer adds what it picks up in Channel 2 to what it picks up in Channel 1. But this means also that it adds environmental (magnetic) noise. The second option would seem at first to carry no advantage -- it cancels out Channel 1 and Channel 2 -- however this means that it cancels out environmental (magnetic) noise -- and there is plenty. Therefore it boosts sensitivity -- the signal that matters is drawn out. In the first case, the two sensors would likely be mounted close together. In the second case, they would likely be mounted far apart. OBSERVATION: This all assumes, however, that the two channels act in precisely the same way. If, however, each channel picks up a trembling pin, it is a major ambition to balance them. Most importantly, to achieve this, one builds both channels identically. The quest continues ...

POSTSCRIPT: I chose the second option. It stabilised everything. Which means I can try to push up the sensitivity. So far, it picks up a moving paper clip at  60 mm, and a moving car at 10 000 mm (10 metres). This is direct detection. Through indirect means, one can do far more.