Fiber-Optic Tachometer Borescope for Gas Turbine Shaft Monitoring
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Solution Overview
Problem
Gas turbine engines face challenges in identifying engine faults due to lack of accurate positional information during operation, leading to potential failures and costly replacements, as existing methods are intrusive, unreliable, or require shutdowns, and existing sensors require modifications to the machine construction.
Innovation Solution
A fiber-optic tachometer borescope system with a focusing tip and Y-shaped fiber optic cable provides a non-intrusive, once-per-revolution phase-dependent inspection and positionally aware tangential velocity measurement, using a fiber-optic bundle to emit and receive light from a rotating surface, allowing for remote visual inspection and data collection without contact or modification of the shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed reference point is positioned on the shaft surface, then positional information can be obtained, but the method is intrusive to normal turbine operation and requires shutdown conditions
Solution Approach 1:
The patent uses a borescope as an intermediary device to observe the shaft surface remotely through an access port, eliminating the need for direct contact or attachment to the shaft. This allows positional information to be obtained during operation without intrusive modifications or shutdowns.
Solution Approach 2:
The patent replaces mechanical contact-based positioning methods with optical sensing. A tachometer device with optical sensors detects reflective paint markings through the borescope, allowing non-contact measurement of shaft position and velocity during operation.
2Measurement precision
If reflective paint is applied to the shaft for marking, then a once-per-revolution signal can be obtained, but the paint loses its reflective characteristics soon after being subjected to high temperatures and particulate matter
Solution Approach 1:
The patent applies protective coating over the reflective paint marker before operation to shield it from high temperatures and particulate matter. This preliminary protective action extends the reliable service life of the paint marker during turbine operation.
Solution Approach 2:
The borescope acts as an intermediary that allows observation of the paint marker without exposing it to harsh conditions. The optical system transmits images of the marker through the access port, enabling measurement without direct exposure to hot gas and particulates.
3Measurement precision
If the probe is positioned close to the shaft for measurement, then measurement accuracy improves, but the closest point to the shaft must be several inches away due to rotating compressor blades
Solution Approach 1:
The patent transitions from radial measurement approach to axial measurement approach by observing the shaft surface through the longitudinal access port. This dimensional change allows the borescope to position itself axially close to the measurement point without interfering with rotating compressor blades.
4Reliability
If magnetic or radio frequency sensors are used to detect engine vibration, then impending problems can be detected, but special treatment or changes to the materials used in machine construction are required
Solution Approach 1:
The patent replaces magnetic or radio frequency sensors with optical sensing through the borescope. This substitution eliminates the need for special treatment or modifications to machine construction materials, as optical sensors can detect shaft position and vibration through the existing access port without contacting or modifying the turbine components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate positional data collection and fault identification without shutdowns, reducing the need for costly replacements and improving operational efficiency by providing reliable, real-time monitoring of gas turbine engines and other moving devices.
Implementation Method 1
using a fiber-optic bundle to emit and receive light from a rotating surface
Data Source
AI summary
This present specification provides, amongst other things, an electro-optical monitoring system for obtaining a once-per-revolution signal based on the surface reflection of a rotating device that mandates non-contacting sensor input in potentially hostile environments. The system can use optical and electronic sections to illuminate and detect surface reflections from the rotating surface using existing mounting locations on the periphery of the machine to be measured. The electronic portion is configured to determine a unique mark as the once-per-revolution marker or allow an attending operator to assign a specific marker based on the observed reflected pattern. The optical portion consists of a light source, receiver, and optics that allow for focused and directed light paths.