The test rig for a one stage transonic compressor is based on an open-circle concept. Air is sucked into the compressor via a throttle and a settling chamber. The massflow is measured at the calibrated inlet bellmouth. At the compressor outlet the air is guided through a throttle and a collector box and emitted to the ambience. The compressor is driven by an 800 kW electrical drive. The speed transformation from motor speed to compressor speed is achieved by a planetary gearbox. Measurement of compressor performance and efficiency is realized by a torquemeter.