The plasma analyzer instrument carried by the Pioneer 11 spacecraft looked toward the Sun through a hole in the spacecraft's large dish-shaped antenna. The solar wind entered the plasma analyzer apertures between 2 quadraspherical plates where the direction of arrival, the energy, and the number of ions and electrons making upthe solar wind were measured.
The instrument had a high resolution and a medium resolution analyzer to detect particles of different energy levels. Energies ofthese particles were described in terms of electron volts (eV).
A voltage was applied across the quadraspherical plates in a maximum of 64 steps, at a rate of one step per spacecraft revolution, to count particles in discrete energy ranges. Direction of particle travel was found from the way the instrument was pointed and fromthe particular target within the instrument that detected it.
The high resolution analyzer had 26 continuous-channel multipliers (CCM) to measure the number of ions per second between 100 and 8,000 electron volts. The medium resolution analyzer had five electrometers to count ions of 100 to 18,000 electron volts andelectrons of 1 to 500 electron volts.