Implementation of the first level surface detector trigger for the Pierre Auger Observatory Engineering Array

The Pierre Auger Observatory studies ultra-high energy cosmic rays in the range of 1018eV up to the highest energies. The apparatus reaches full sensitivity above 1019ev. The southern hemisphere site is currently under construction. When completed, the surface array at this site will contain 1600 water Cherenkov detector stations distributed over 3000km2. Prior to proceeding with full-scale construction, a prototype “Engineering Array”, consisting of 40 detector stations was tested. This paper describes the implementation of the first level surface detector trigger used in the engineering array.