Research On Tip Clearance Measurement With Chip Capacitor

Blade tip radial clearance of the aero-engine is very important for the wholeengine. When tip clearance (TC) is relatively large, it will reduce the performance ofengine. Contrarily, when tip clearance is relatively small, it will cause potentialsafety hazard. As a result, controlling engine tip clearance and maintaining it inrational range is of significant meaning for improving engine performance andguaranteeing engine security.At present, detection methods for tip clearance in the world include dischargeprobe method, eddy current method, capacitance method, optical fiber method,laser method, supersonic method, X-ray method and microwave method, etc. Amongthem, capacitance method is widely used due to its characteristics of simplestructure, good sensitivity, high resolution and non-contact measurement. To thequestion of clearance detection, the subject designs and researches on clearancedetection system by using the principle of amplitude-modulation type capacitancemethod.The research focus of the subject mainly includes the following aspects：1. Aiming at the problems that blade tip clearance of the engine is relativelysmall in the subject and it is difficult to put current capacitance sensor probe intoclearance, the author provides the suggestion to produce new type of probe by usingprinted circuit board technic and discusses on the problems might encountered inprobe designing process. Besides, the author also conducts electrostatic fieldsimulation and experimental analysis of designed probe.2. The subject designs modulation circuit of amplitude-modulation typecapacitance method to realize the transformation from sensor displacement signal tovoltage signal. Aiming at the influence of stray capacitance and cable distributioncapacitance in modulation circuit of operation amplification type, the subject adoptsdriving cable technique to protect the circuit.3. The subject designs stable demodulation circuit. After rectifying, band-stopfiltering and low-pass filtering, modulation signal can output constant direct currentand realize demodulation of the signal.4. The subject designs sensor AD acquisition module and puts up experimentalplatform so as to implement experimental test and performance analysis on sensorsystem.The experimental result indicates that in the effective detection range of0~300μm， the stability of the whole sensor system is better than7m/30min and its resolution can reach up to1m and repeatability experimental standard deviation is±1m. But the linearity error of the system is not good, it need a non-linearcorrection in subsequent operations.In conclution, the method provided in the subject to produce probe by applyingprinted circuit board technic is effective and lamellar capacitance displacementsensor developed in the subject can fully reach the design index of the subject.