Moisture Measurement Device Using Frequency-Modulated Laser Light
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Solution Overview
Problem
Existing moisture measurement devices using infrared absorption spectroscopy face challenges in accurately monitoring interfering moisture levels, which can affect measurement accuracy and system stability, especially in environments with varying gas pressures and high vacuum conditions.
Innovation Solution
A moisture measurement device that employs frequency-modulated laser light with adjustable modulation amplitudes to differentiate between target moisture in a sample cell and interfering moisture in the optical path, allowing for continuous monitoring and calculation of both moisture concentrations using synchronous detection signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If infrared absorption spectroscopy is used to measure moisture concentration in gas, then measurement speed and non-contact capability are improved, but the ability to measure minute quantities of moisture deteriorates
Solution Approach 1:
The patent applies periodic frequency modulation to the laser light source, modulating the frequency at a specific frequency f. By using synchronous detection at integer multiples of this modulation frequency, the system extracts weak absorption signals from noise, enabling detection of minute moisture quantities while maintaining fast measurement speed. The periodic modulation converts static absorption measurements into dynamic signal processing that enhances sensitivity.
Solution Approach 2:
The patent employs frequency modulation of the laser light, which creates oscillating absorption signals at the modulation frequency and its harmonics. This vibration in the frequency domain allows synchronous detection to isolate the moisture absorption signal from background noise, improving the detection limit for minute moisture amounts while maintaining rapid measurement capability.
2Ease of operation
If laser light passes through optical path space to detect moisture in sample cell, then non-contact measurement capability is improved, but interference from atmospheric moisture in optical path deteriorates measurement accuracy
Solution Approach 1:
The patent segments the total absorption signal into two distinct components by utilizing different harmonic detection frequencies. The first synchronous detection at frequency f measures moisture in the sample cell, while the second synchronous detection at frequency 2f measures interfering moisture in the optical path. This segmentation allows independent measurement and subsequent subtraction of interference signals, maintaining non-contact capability while improving accuracy.
Solution Approach 2:
The patent uses harmonic detection signals as intermediaries to separately probe different moisture sources. The fundamental frequency signal acts as an intermediary for sample cell moisture measurement, while the second harmonic signal serves as an intermediary for optical path moisture measurement. These intermediary signals enable indirect separation and quantification of interfering moisture without requiring physical separation of the optical paths.
3Measurement precision
If synchronous detection at integer multiples of modulation frequency is used, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent employs a universal synchronous detection system that can operate at multiple frequencies (f, 2f, and other integer multiples) using the same hardware components. The frequency modulation unit and synchronous detection unit serve multiple functions by detecting different harmonics of the same modulation frequency, enabling both sample cell and optical path moisture measurements without requiring separate detection systems for each function.
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 and continuous monitoring of moisture concentrations, preventing measurement inaccuracies and system abnormalities by distinguishing between target and interfering moisture, even in low-pressure environments, without requiring complex control systems or additional moving mechanisms.
Implementation Method 1
a moisture measurement device that uses absorption of laser light for measuring moisture concentration in a gas
Implementation Method 2
laser light modulated using frequency f and emitted from the laser irradiation unit
Implementation Method 3
the detection signal is synchronously detected using a frequency that is an integer-multiple of frequency f
Implementation Method 4
transmitted laser light is analyzed to determine moisture concentration from the amount of absorption by the moisture in the gas
Data Source
AI summary
Modulation amplitude used for frequency modulation of laser light is set to a1 (<a2) (S1), and laser light is irradiated to a sample state in that state. When moisture concentration is calculated based on secondary harmonic synchronous detection signal that is obtained by synchronous detection of detection signal from transmitted light, the effects of interfering moisture in the optical chamber is ignored, and moisture concentration of the gas to be measured in the sample cell is obtained (S2). If, for example, a high vacuum is created inside the sample cell and the concentration becomes less than the detectable limit (“YES” in S3), the modulation amplitude is switched to a larger amount a2 (S4). By so doing, the detection sensitivity to interfering moisture in atmosphere at atmospheric pressure is increased, and the concentration of interfering moisture is calculated based on the secondary harmonic synchronous detection signal (S5).