The main objective of this investigation is to study the temperature, bulk velocity and density of the interstellar neutral helium gas in the vicinity of the solar system. The sensor acts like a pin-hole camera for neutral helium and ultraviolet photon measurements. Mechanical collimators for each of two separate entrance channels suppress charged particle and photoelectron backgrounds. Full opening angles of the two channels are 4.9 and 7.4 degrees, respectively, corresponding to geometric factors of 0.13x10^-3 and 0.53x10^-3 cm^2sr. Channel Electron Multipliers (CEM) are used to amplify and count secondary ions or electrons produced by neutral particle impact on a lithium fluoride surface. The latter is periodically refreshed via a heated filament. Neutral helium is preferentially detected by usage of an electrostatic field to accelerate positive secondary Li ions into the CEM's while suppressing secondary electrons from ultraviolet background. Alternatively, the secondary electrons may be accelerated for ultraviolet measurements. Both sensor channels are always operated in either ion or electron mode. The sensor detects neutral helium at energies above 30 eV, corresponding to interstellar helium flow speeds of 27 km/sec with respect to the spacecraft. Peak secondary production efficiency occurs at energies above 80 eV and is comparable for ions and electrons. The sensor is sensitive to heavier neutral atoms but not to hydrogen. The relatively higher abundance of helium dominates the response for Z>1. The threshold speed for neutral helium is achieved during the first six months after launch, at other times when the spacecraft and helium flow velocities are sufficiently antiparallel, and for extended intervals near perihelion. The whole celestial sphere can be scanned by using the spacecraft rotation and a mechanical stepping platform on which the sensor is mounted. The instrument is fully described in Witte, M., et al., Astron. Astrophys. Suppl. Ser., 92(2), 333-348, Jan. 1992 (NSSDC TRF ID B40459-000A).