Emittance measurements in the CERN PS complex

The LHC project, with its demand for small emittance beams and their monitoring, constitutes a challenge for the instruments of the CERN PS complex used hitherto to measure emittances of generally larger beams with less precision. Among these instruments, one (Beamscope) measures the betatron amplitude distribution, while the other two (SEM-grids, fast wire scanner) are recording the projected beam density. Emittances are quoted as derived from one standard width of the projected beam density, and the goal is to provide figures which refer to this definition regardless of the measurement instrument and method. The paper recalls the principles of these measurement systems and describes the mathematical methods applied to eliminate noise and measurement errors, to transform between the phase plane and its projection and the formalism used to determine the matching between machines.