I am building a payload for a high-altitude Balloon launch in the club I started which will be measuring DC voltages (electric field) at different altitudes using a wire dipole or two metal plate formation.
I obviously need a low noise amplifier to even register any data in the logger, and we are not worried about polarity, only magnitude.
To do this, I am thinking an instrumentation amplifier fed from the metal plates to the data-logging device, but I am facing a problem, how can I assure the DC amplifier is only measuring positive values? Even some good diodes have a few hundred millivolt drop, which would not be suitable for the experiment. A transformer would not work because this is only DC we are working with (even if it was AC, the high input impedance requirement would not be fulfilled).
Any ideas on rectification or ways to amplify the small DC signals which we can't be 100 percent sure the polarity is constant.