Blade tip clearance and time of arrival immediate measurement method using an optic probe

The measurement of the tip clearance and the time of arrival of every single blade in rotating turbo machinery is the starting point to characterize the performance of a rotating turbine. The type of sensors employed to acquire the data for this analysis are mainly non-intrusive such as optic, capacitive, eddy-current and microwave sensors. This paper introduces the method employed to calculate the tip clearance and time of arrival of the blades using a fibre-optic probe. The time of arrival of each blade is evaluated right after detecting its pass, and before the next blade finishes passing in front of the sensor. Both parameters are available from that moment for further analyses by a post-processor device. During the acquisition of the sensor data, the maximum and minimum tip clearance and time of arrival are also computed for the current measurement and their values are also made available for post-processing. The whole algorithm has been developed in a single core using a hardware description language and implemented on a programmable logic device which allows for easy extension of the system when more than one sensor monitoring is required.