The thesis presents a new ultrasound based in situ measuring system, which is able to determine the wall thickness variations of thin-walled steel rings from signal phase measurements. It is applied in the workspace of a horizontal turning center and delivers information about the ring behavior for different turning operations and clamping conditions. Additionally, it can be used to determine the set-values for a control system, which establishes a constant wall thickness by fast movements of a turning tool servo for clamping-distorted rings. The measuring system consists of a signal generator, control electronics, a 15 MHz transducer and a PC system for data acquisition and evaluation. It is operated in the impulse-echo mode with a burst signal of 20 sine periods and uses the metal working fluid of the turning center as the coupling fluid for the sound propagation between transducer and ring. The wall thickness measuring range is 0 to 600 micrometer with an estimated uncertainty of 6 micrometer.