Gas Velocity Sensor with Fabry-Perot Interferometer Feedback
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Solution Overview
Problem
Existing gas velocity sensors, particularly those using optical techniques, face challenges with variable and unpredictable output pulse amplitudes leading to amplitude noise, and temperature variations causing false air velocity measurements due to thermal expansion and laser frequency changes.
Innovation Solution
The solution involves a gas velocity sensor system with a spatial filter and compensation spatial filter, using a Fabry-Perot interferometer with a movable reflector and piezoelectric actuator, which generates compensation signals to stabilize light intensity and frequency, reducing noise and temperature-induced errors, and a method to measure and adjust light amplitudes for accurate Doppler shift detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser is used to illuminate gas and an interferometer is used to measure Doppler frequency shift, then air speed measurement capability is improved, but amplitude noise increases due to variable output pulse amplitudes
Solution Approach 1:
The patent implements feedback control by monitoring the actual laser output pulse amplitude and adjusting the laser drive signal accordingly. A detector measures the backscattered light intensity, and this information feeds back to the laser control system to stabilize the output amplitude, thereby reducing amplitude noise while maintaining measurement precision
Solution Approach 2:
The patent changes the operating parameters of the laser by adjusting the drive current or voltage dynamically. By modifying the laser excitation parameters in real-time based on measured output levels, the system compensates for amplitude variations and reduces noise without sacrificing measurement capability
2Duration of action of stationary object
If temperature variations occur in the laser or interferometer, then device operation continues, but false air velocity indications are generated
Solution Approach 1:
The patent employs feedback control to monitor temperature variations in the laser and interferometer components. Temperature sensors detect changes, and this information feeds back to adjustment mechanisms that compensate for thermal effects, maintaining measurement accuracy while allowing continuous operation
Solution Approach 2:
The patent introduces temperature compensation as an intermediary mechanism between the temperature variations and the measurement system. By using reference measurements and compensation algorithms, the system isolates the actual air velocity measurement from temperature-induced errors, allowing continuous operation without false indications
3Measurement precision
If the interferometer is used to measure backscattered light, then air flow velocity can be determined, but thermal expansion causes inaccurate measurements
Solution Approach 1:
The patent explicitly accounts for thermal expansion effects in the interferometer by incorporating temperature compensation mechanisms. By measuring temperature changes and calculating the resulting dimensional variations, the system compensates for thermal expansion to maintain measurement accuracy
Solution Approach 2:
The patent uses feedback control to monitor the interferometer's dimensional changes due to thermal expansion. Temperature sensors and reference measurements provide feedback that drives compensation adjustments, maintaining accurate air flow velocity determination despite thermal effects
4Duration of action of stationary object
If laser frequency changes occur, then device operation continues, but false velocity measurements are produced
Solution Approach 1:
The patent implements feedback control to monitor laser frequency changes in real-time. Frequency sensors detect drift, and this information feeds back to the laser control system to adjust the drive parameters and maintain stable frequency, ensuring accurate velocity measurements during continuous operation
Solution Approach 2:
The patent introduces frequency stabilization as an intermediary mechanism between laser frequency changes and the velocity measurement system. By using reference frequency comparisons and stabilization circuits, the system isolates the velocity measurement from frequency-induced errors while maintaining continuous operation
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
This approach significantly reduces amplitude noise and temperature-related errors, enhancing the sensor's ability to accurately measure air flow velocity by maintaining consistent light power levels and compensating for frequency shifts, resulting in improved sensitivity and reliability.
Implementation Method 1
an optical interferometer for receiving light backscattered from the gas... variations in the frequency of received backscattered light cause corresponding variations in the intensity of light reaching the backscatter photodetector
Implementation Method 2
the spatial filter having a structure of transparent and opaque regions corresponding to a predetermined interference pattern by the interferometer such that, in operation, variations in the frequency of received backscattered light cause corresponding variations in the intensity of light reaching the backscatter photodetector
Implementation Method 3
at least one of which is moveable under the influence of an electromechanical actuator... the compensating means are operable to generate the compensation signal to control the actuator
Implementation Method 4
a laser is used to illuminate a gas and the Doppler frequency shift due to gas flow in the light scattered by the gas molecules is measured
Data Source
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AI summary
This invention relates to a gas velocity sensor and to a method of determining gas velocity. The invention provides a method an apparatus for determining gas velocity by generating transmitted radiation having an expected transmission frequency;detecting backscattered radiation; and determining gas velocity in dependence upon any Doppler shift of the frequency of the backscattered radiation; determining a transmission frequency of the transmitted radiation; detecting any difference between the measured transmission frequency and the expected transmission frequency and generating a feedback signal therefrom; determining gas velocity using said feedback signal.