Abstract: The system is used to measure the gap between the turbine engine compressor blade tip and the compressor case. The measurement is accomplished while the engine is running. This system has several unique features which minimize problems plaguing earlier systems. These include tuning stability and sensitivity drift. Both these problems are intensified by the environmental factors present on compressors, i.e., wide temperature fluctuations, vibrations, conductive contamination of probe tips and others. The circuitry in this new system provides phase lock feedback to control tuning and shunt calibration to measure sensitivity. The use of high frequency excitation lowers the probe tip impedance, thus minimizing the effects of contamination. The ability to control tuning and to calibrate has been demonstrated.