Compressor Blade Clearance Measurement Using Capacitance and Phase Lock Techniques,
AIR FORCE WRIGHT AERONAUTICAL LABS WRIGHT-PATTERSON AFB OH
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The clearance measurement system described in this paper 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. Use of high frequency excitation lowers the probe tip impedance thus minimizing the effects of contamination. A prototype has been built and tested. The ability to control tuning and to calibrate has been demonstrated. An eight channel system is now being constructed for use in the Compressor Research Facility at Wright-Patterson AFB OH.
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