Combined Paper Moisture and Temperature Sensor
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Solution Overview
Problem
Existing moisture sensors in papermaking processes face significant errors due to temperature sensitivity, which affects the accuracy of moisture content measurements, as the absorption of infrared radiation by paper web varies with temperature.
Innovation Solution
A method that analyzes the absorption spectrum of water in the infrared region to determine the central wavelength position of the moisture peak, allowing for the calculation of both moisture content and temperature, using a tunable laser diode to direct radiation and compute the moisture temperature from the peak position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional infrared moisture sensors are used to measure moisture content, then moisture measurement can be achieved, but temperature sensitivity causes significant measurement errors
Solution Approach 1:
The patent segments the infrared spectrum into multiple discrete wavelength channels, with at least one channel tuned to the water absorption peak wavelength and another to a reference wavelength away from absorption peaks. By measuring radiation intensity at these separated wavelength segments and comparing them, the system isolates the moisture-specific signal from temperature-induced spectral variations, thereby resolving the temperature sensitivity problem while maintaining moisture measurement accuracy
Solution Approach 2:
The patent changes the wavelength parameter of the infrared radiation by using multiple discrete wavelength channels, including at least one at the water absorption peak and another at a reference wavelength. This parameter change allows the system to differentiate between temperature effects (which affect all wavelengths) and moisture effects (which specifically affect absorption peak wavelengths), eliminating temperature sensitivity errors
2Measurement precision
If broadband infrared source with narrow-band filter is used, then moisture measurement is possible, but the measurement is affected by temperature-induced spectral shifts
Solution Approach 1:
The patent divides the infrared spectrum into multiple discrete wavelength segments using a wavelength selection mechanism that can tune to specific wavelengths. By segmenting the spectrum and selecting at least one wavelength at the water absorption peak and another at a reference wavelength, the system can separately measure moisture-specific absorption and temperature-induced spectral shifts, then compensate for the latter to maintain spectral stability
Solution Approach 2:
The patent implements a feedback mechanism where radiation intensity at the water absorption peak wavelength is compared with intensity at a reference wavelength. This comparison provides feedback about temperature-induced spectral shifts, allowing the system to compensate for these shifts and maintain stable infrared absorption spectrum measurements despite temperature variations
3Measurement precision
If scanning sensors are used for on-line measurement, then quality monitoring is achieved, but measurement speed and real-time control are limited
Solution Approach 1:
The patent transitions from periodic scanning measurements to continuous real-time measurement by maintaining constant irradiation of the paper web with infrared radiation at multiple discrete wavelength channels. This continuous action allows simultaneous monitoring of moisture content and temperature without the speed limitations of scanning, enabling real-time process control while maintaining measurement precision
Solution Approach 2:
The patent adds the wavelength dimension by using multiple discrete wavelength channels instead of a single scanning wavelength. This dimensional change from temporal scanning to spectral multiplexing allows parallel measurement of multiple parameters (moisture content, temperature) simultaneously, dramatically increasing measurement speed while maintaining accuracy
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 enables high-speed, real-time measurement of moisture temperature and content, reducing temperature-related errors and improving the accuracy of moisture control in papermaking processes.
Implementation Method 1
the absorption spectrum of water in the infrared (IR) region
Implementation Method 2
directing infrared radiation from a tunable laser diode
Data Source
AI summary
Temperature measurements of sheet material such as paper can be obtained directly from an analysis of the absorption spectrum of water in the infrared region. The technique is based in part on the recognition that the central wavelength position of a selected moisture peak is dependent upon the sheet temperature; the wavelength position also has a known temperature sensitivity. Thus, once the wavelength position of this moisture peak is ascertained, the moisture temperature of the product being monitored can be calculated. The position of the moisture peak is preferably obtained from the derivative of the peak. By measuring the size of the infrared absorption and the wavelength position of the absorption peak, both the moisture content and the moisture temperature of the sheet material can be determined. The data is used for process control. Tunable laser diodes are particularly suited as the source of infrared radiation for the temperature sensors.