The process of exposing (charging) and shielding (discharging) the sensor plate from the electrical field is accomplished by means of a rotary shutter (see Figure 5. Rotary Shutter.), consisting of a motor-driven, mechanically complementary rotor/stator pair. As the motor rotates, the shutter alternately opens (see Figure 6.) to allow the external electric field to charge the sensor plate, and then closes (see Figure 7.) to shield the sensor plate to allow it to discharge, or reset, in preparation for the next measurement. The shutter rotates at a speed of 1650 revolutions per minute, and opens and closes four times per revolution thus producing 6,600 samples per minute.