| 摘要 |
A system for use in a gas-turbine engine, for controlling the clearance between the tips of the blades and a surrounding shroud, has a probe mounted in the shroud. A microwave oscillator supplies microwave energy to the probe which propagates energy towards the blades and receives energy reflected from the blades. A mixer is mounted remote from the probe and mixes the energy reflected from the blades with a reference signal derived either from energy transmitted by the oscillator or from the energy reflected by the tip of the probe. This produces interference dependent upon the phase difference between the energy reflected by the blades and the reference signal. From this phase difference, the system derives an indication of the separation of the blades from the probe and uses this to displace the shroud along its length, thereby altering the clearance between the tips of the blades and the shroud.
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