TDLAS Gas Sensor Digital Filter for Integer Arithmetic
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Solution Overview
Problem
The existing TDLAS measurement method requires high calculation accuracy for phase-sensitive detection, which is not met by using Programmable Logic Devices (PLDs) due to their lower computing accuracy, making it difficult to extract DC components effectively.
Innovation Solution
A gas concentration measurement device that employs a combination of a digital filter for reducing AC components corresponding to the modulation frequency and a low-pass filter, allowing for integer arithmetic processing to achieve sufficient damping properties for extracting DC components, using a moving average over one cycle of the frequency for initial filtering and an IIR-type low-pass filter for further signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a PLD is used for digital filtering in phase-sensitive detection, then the operating speed is increased and circuit size is reduced, but the computing accuracy becomes too low to extract DC components
Solution Approach 1:
The filtering process is divided into two separate stages: first a band-pass filter to remove frequencies far from the modulation frequency, then a low-pass filter to extract the DC component. This segmentation allows each filter to operate with reduced complexity requirements, enabling accurate DC extraction using integer arithmetic in PLD.
Solution Approach 2:
The patent changes the approach to filtering by introducing a two-stage process with specific cutoff frequencies. The band-pass filter removes frequencies below and above the modulation frequency range, while the low-pass filter extracts DC components. This parameter-based filtering strategy makes the system compatible with integer arithmetic while maintaining accuracy.
2Measurement precision
If a digital low-pass filter with extremely steep damping property is used to extract DC components, then the measurement sensitivity is improved, but the calculation accuracy requirement increases beyond what integer arithmetic can provide
Solution Approach 1:
The filtering function is segmented into two distinct filters with different characteristics. The band-pass filter handles high-frequency noise removal, while the low-pass filter handles DC extraction. This segmentation reduces the damping requirement for each individual filter, making the overall system achievable with integer arithmetic.
Solution Approach 2:
The band-pass filter acts as an intermediary stage between the raw detection signal and the final DC extraction. It pre-processes the signal by removing frequencies that would interfere with the subsequent low-pass filtering, thereby reducing the burden on the low-pass filter and enabling accurate DC extraction with integer arithmetic.
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 accurate extraction of DC components using integer arithmetic, improving the signal-to-noise ratio and measurement sensitivity, allowing for higher operating speeds and reduced circuit size and power consumption, while maintaining the advantages of PLDs in device control and circuit integration.
Implementation Method 1
a photodetector for detecting the laser light that has passed through the measurement cell
Implementation Method 2
a technique called the Tunable Diode Laser Absorption Spectroscopy measurement... the gas contains a variety of components, each of which absorbs light at a specific wavelength or wavelengths
Implementation Method 3
the laser beam undergoes strong absorption at around the wavelength or wavelengths characteristic of a target component of the gas
Data Source
AI summary
A gas concentration measurement device which utilizes a TDLAS measurement method, and in which the phase-sensitive detection can be performed by digital processing using an integer-arithmetic device, is provided. In the gas concentration measurement device according to the present invention, AC components corresponding to integer multiples of a modulation frequency f contained in an input signal are removed by taking a moving average of data obtained from an output signal of a multiplier 62 for a period of time corresponding to one cycle of the modulation frequency f . As a result, a DC component in the output signal of a digital filter 63 relatively increases, making it easier to extract the DC component by a digital low-pass filter 64, so that a sufficiently accurate phase-sensitive detection can be made even if a digital processing based on integer arithmetic is used.