| 摘要 |
A direct digital measurement proportional to tip clearance of the blades of a turbomachine is obtained by placing at each position on the casing where clearance is to be measured a pair of optical sensors. Each sensor comprises the ends of fiber-optic bundles communicating with a remotely positioned light emitter and a light detector. The sensors in the casing are spaced a short distance apart in the circumferential direction but both located at the same axial coordinate with respect to the axis of rotation. The two sensors each emit a beam of light at an angle to one another measured in a surface of revolution containing both light beams. The light reflected and scattered by a blade passing each beam is transmitted back through the adjacent or concentric fiber optics to photodiode detectors. A signal generator producing a stable frequency of pulses in the megacycle range provides the digital time base. As a rotating blade intercepts the first light beam of the sensor pair, the signal from its photodiode starts a counter which counts cycles (pulses) from the signal generator. As the blade in its movement intercepts the second light beam, the signal from its photodiode stops the counter. Another similar (single) sensor, monitoring a point relative to the turbomachine disc or shaft, starts and stops another counter which records the number of cycles or pulses which occurred during one revolution of the shaft. By dividing the number of counts measured by the sensor pair by the number of counts measured during one shaft revolution, a number is obtained which is insensitive to rotational speed and since the light beams of the sensor pairs are at an angle to one another, this number varies linearly with respect to tip clearance.
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