A more useful configuration is the quadrant electrometer, shown in Figure 1.7.
Four fixed plates realize four quadrants and surround a movable vane suspended by a torsion fiber at the center of the system.
The opposite quadrants are electrically connected together, and the potential difference (U1 – U2) is applied.
The moving vane can be either connected to potential U1 or U2 , or energized by an independent potential U3.