Fabry-Perot Interferometer Gas Analysis with Periodic Mirror Detuning
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Solution Overview
Problem
Gas analysis systems with thermal sensors, particularly those using pyroelectric detectors, face challenges in achieving reliable calibration and rapid detection of gas concentration due to the long time constants of these sensors, especially when analyzing anesthesia gases like nitrous oxide and carbon dioxide, as they react slowly to changes in radiation intensity.
Innovation Solution
A method involving a gas analysis system with a Fabry-Perot interferometer and thermal sensors, where time signal pulses are generated at a constant period, and the distance between the interferometer mirrors is continuously adjusted, allowing for the detection of voltage changes at predefined intervals, enabling accurate measurement of wavelength intervals and intensity determination, even with long-time constant thermal sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal sensors are used to detect radiation in the long-wave infrared range, then the sensor can detect anesthesia gases like nitrous oxide and carbon dioxide, but the sensor reacts slowly to changes in radiation intensity due to long time constants
Solution Approach 1:
The patent applies periodic action by continuously detuning the Fabry-Perot interferometer with a predefined voltage, causing the distance between mirrors to oscillate periodically. This periodic modulation of the interferometer's wavelength sensitivity, combined with the thermal sensor's integration effect over each oscillation period, enables reliable gas detection while the sensor's long time constant acts as a natural low-pass filter that smooths high-frequency noise without significantly delaying the detection of genuine gas concentration changes
Solution Approach 2:
The patent implements continuity of useful action by continuously oscillating the interferometer's mirror distance and continuously detecting the sensor signal throughout the oscillation cycle. Rather than taking discrete measurements, the system maintains continuous detection and processing of the sensor output, ensuring that gas concentration information is constantly updated while the thermal sensor's long time constant is compensated by the continuous nature of the measurement process
2Measurement precision
If the Fabry-Perot interferometer is continuously detuned to scan through wavelength ranges, then an absorption spectrum can be determined, but the process requires great expenditure of time which delays gas concentration determination
Solution Approach 1:
The patent transforms the traditional slow sequential wavelength scanning into a rapid periodic oscillation of the interferometer. By continuously oscillating the mirror distance at a predefined frequency, the system rapidly cycles through the wavelength range of interest, and the thermal sensor integrates the signal over each period, providing both spectral information and rapid response without requiring time-consuming sequential measurements
Solution Approach 2:
The patent applies preliminary action by pre-calibrating the relationship between the interferometer's mirror distance and the corresponding wavelength sensitivity. This preliminary establishment of the wavelength-distance mapping allows the system to directly interpret sensor signals during continuous oscillation without requiring real-time spectral analysis, thereby eliminating the time-consuming post-measurement spectrum analysis step
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 allows for reliable gas concentration determination by associating voltage signals with specific wavelength intervals, improving sensitivity and reducing the time required to detect changes in gas concentrations, thus overcoming the limitations of thermal sensors with long time constants.
Implementation Method 1
a Fabry-Perot interferometer which has a first and a second semireflecting mirror that are arranged parallel to one another, and a device for changing the distance between the mirrors
Implementation Method 2
a thermal sensor, the thermal sensor being configured such that the electromagnetic radiation falling on it causes a change in a voltage between electrodes provided on it
Data Source
AI summary
A method for signal detection with a gas analysis system (1, 1′) includes a radiation source (3); a gas measuring section (9) containing gas to be measured; a Fabry-Perot interferometer (13); a thermal sensor (17) configured to cause a change in voltage between electrodes with electromagnetic radiation falling thereon and arranged such that radiation released by a second interferometer mirror falls on the thermal sensor. The method includes irradiating the gas measuring section with radiation source radiation, continuously increasing or decreasing a distance of interferometer mirrors during a generating of time signal pulses at a constant period of time from one another. After a predefined number of time signal pulses, the voltage generated between the electrodes is detected and stored as a measured signal value. After a further predefined number of time signal pulses, the voltage generated between the electrodes is detected again and stored as a measured signal value.