Fast-Fourier-transform-based open-circuit measurement method for smoke plume opacity

Abstract

The invention discloses a fast-Fourier-transform-based open-circuit measurement method for the smoke plume opacity, which comprises the following steps of carrying out pulse modulation on a light source; after a program is read into a time-domain pulse signal, carrying out segmentation on the pulse signal firstly, and then carrying out fast Fourier transform on each segment of the signal so as to obtain a frequency-domain signal; after a fundamental frequency quantity is subtracted from the frequency-domain signal, carrying out inverse Fourier transform so as to obtain a time-domain signal after stray light filtering. After an original signal is processed, the opacity is calculated according to a formula. The method disclosed by the invention has the advantages that stray light can be restrained powerfully, and an operation of measuring the background value or adding components such as an optical filter is not required; the method is easy to operate and strong in reliability and adaptability, and can realize the continuous automatic measurement.

Description

technical field [0001] The invention relates to the technical field of urban air quality monitoring and management, in particular to an open-circuit measurement method for smoke plume opacity based on fast Fourier transform. Background technique [0002] Plume opacity refers to the degree of light attenuation when passing through the plume. The opacity directly reflects the content of particulate matter in the plume. It is an effective method to evaluate the pollution degree of the plume and has been approved by the US National Environmental Protection Agency. listed as a reference indicator 1 . At present, the main methods of opacity detection are naked eye observation, digital photography method and transilluminator observation. 1-3 . Among them, the light source used in the transmissometer observation method is generally an artificial light source such as LED, tungsten halogen lamp or laser. The degree of attenuation reflects the opacity of the plume. The transmissome...

AI Technical Summary

Problems solved by technology

During open-circuit observation, after the light from the sun or artificial light source is scattered or diffusely reflected by the plume itself and the surrounding environment, some light will always enter the detector along the direction of the signal beam, causing stray light

The presence of stray light reduces the signal-to-noise ratio and affects measurement accuracy, especially when observing plumes from fugitive emissions.

At present, there are mainly two methods for suppressing stray light. One method is to regard the measured value when there is no smoke plume in the measurement area as the background value, and the difference between the measured value and the background value when there is smoke plume passing through is regarded as the measurement result. The method improves the signal-to-noise ratio to a certain extent, but it cannot overcome the influence of stray light caused by the scattering of light by the plume itself, especially the white plume, whose scattering effect on light is very obvious

Another method is to add a filter at the front end of the detector to filter out the light outside the wavelength range of the light source, so as to achieve the purpose of suppressing stray light. In particular, the spectral wavelength range of sunlight overlaps with the working wavelength range of the transmissometer, resulting in a considerable portion of stray light that cannot be filtered out

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