It consists of an industrial computer with a Pentium processor. Depending on actual system pressure, the controller decides which compressor should run to keep pressure constant. Compressor selection (cut ---in and cut ---out) and the acquisition of all data from the compressor packages takes place via the Profibus. Compressor load can also be controlled via the volt ---free outputs of Sigma Air Manager. All other volt ---free signals from the air supply system are recorded via input modules.