A method and device for detecting formaldehyde concentration based on infrared absorption spectroscopy

Abstract

The invention discloses a formaldehyde concentration detection method and device based on infrared absorption spectrum, which simultaneously detect the positions of two infrared absorption peaks of formaldehyde gas to detect the absorption of infrared light by formaldehyde, and finally calculate the formaldehyde concentration; since gases in the atmosphere have their own characteristic absorption peaks, which will not overlap with the two absorption peaks of formaldehyde, the unaffected absorption peak can be selected as the data of the detection concentration, which can greatly reduce the influence of other gases and improve the detection accuracy of the formaldehyde concentration; in the invention, the concentration voltage ratio coefficient k is calibrated in advance, and a reference channel is not set separately, so the detection process can be simplified; in the formaldehyde concentration detection device based on infrared absorption spectrum of the invention, the light source, the detector, the electronic components and the like have long service life, and the use time can be extended; and the device is simple and easy to implement.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronics, electronics and optics technology, and specifically relates to a formaldehyde concentration detection method and device based on infrared absorption spectroscopy. Background Art

[0002] Formaldehyde, with the chemical formula HCHO, is a colorless gas with a strong pungent odor. Formaldehyde is an important organic raw material, mainly used in the plastics industry, synthetic fibers, leather industry, medicine and dyes, etc.

[0003] Formaldehyde is the main pollutant of indoor environmental pollution. Indoor formaldehyde mainly comes from wood-based panels with resin as adhesive. The release pathways include formaldehyde emitted by wood and panel-making materials themselves. Formaldehyde is a raw material poison that can bind to proteins. It has the most prominent impact on human health. The national standard stipulates that the formaldehyde content in indoor air shall not exceed 0.08mg / m 3 Formaldehyde has been identified by the World Health Organization as a carcinogen and teratogen. It is one of the potential strong mutagens and has strong carcinogenic and cancer-promoting effects.

[0004] Although there are many methods for determining formaldehyde, such as spectrophotometry, chromatography, fluorescence, chemiluminescence, electrochemistry, etc., most of these methods must first use an atmospheric sampler to extract the formaldehyde in the air into an absorption liquid, and then bring it back to the laboratory for analysis. In this case, the experimental cycle is long and is not suitable for rapid detection in public places.

[0005] In the civil and other fields, formaldehyde test paper and reagent detection methods are usually used. This is a chemical method with simple materials and low cost, but it mainly relies on the human eye and makes judgments through visual colorimetry, which has low sensitivity and large measurement errors. At the same time, this method is one-time and the reaction liquid cannot be reused. Real-time monitoring cannot be completed.

[0006] Electrochemical sensors are also commonly used in the civilian field. This sensor uses an electrochemical method, and formaldehyde reacts with the reaction material, thereby changing the conductivity of the material. This method has a fast detection speed. However, the materials involved in the chemical reaction in the electrochemical sensor will continue to decrease as the reaction proceeds, so the service life is short and needs to be replaced frequently. In addition, various gases in the air, such as methane, ammonia and other volatile organic compounds (VOCs), deliberately participate in redox reactions, thereby affecting the readings of the electrochemical sensor, which is called cross-influence. Therefore, this formaldehyde sensor will be affected by multiple gases, resulting in very inaccurate measurement results.

[0007] Providing a formaldehyde detector with accurate measurement results is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0008] In view of this, an object of the present invention is to provide a formaldehyde concentration detection method and device based on infrared absorption spectroscopy, which can achieve accurate detection of formaldehyde concentration through a simple method and device.

[0009] A formaldehyde concentration detection method based on infrared absorption spectroscopy, comprising:

[0010] An infrared light source with a wavelength range of at least 3.6um to 5.78um is used to irradiate the formaldehyde gas to be tested;

[0011] A filter with a transmission wavelength of 3.6 μm is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the first signal;

[0012] A filter with a transmission wavelength of 5.78 um is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the second signal;

[0013] Determine whether the difference between the first signal and the second signal is within the set range:

[0014] If it is within the set range, the first signal or the second signal value is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured;

[0015] If it is not within the set range, the larger value of the first signal and the second signal is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured;

[0016] The concentration-voltage ratio K is the ratio of the pre-calibrated formaldehyde concentration to the corresponding formaldehyde infrared spectrum voltage value.

[0017] A formaldehyde concentration detection device based on infrared absorption spectrum, comprising: an infrared light source, a first filter, a second filter, a first infrared detector, a second infrared detector, a first amplifier, a second amplifier and a signal processor;

[0018] The infrared light source generates infrared light with a wavelength range of at least 3.6um to 5.78um, and irradiates the infrared light onto the formaldehyde gas to be tested;

[0019] The transmission wavelength of the first filter is 3.6um, and is used to filter the infrared light absorbed by the formaldehyde gas to be measured;

[0020] The transmission wavelength of the second filter is 5.78um um, and is used to filter the infrared light absorbed by the formaldehyde gas to be measured;

[0021] The first infrared detector is used to receive the infrared spectrum after being filtered by the first filter, and convert the optical signal into a voltage signal;

[0022] The second infrared detector is used to receive the infrared spectrum filtered by the second filter and convert the optical signal into a voltage signal;

[0023] The signal processor is used to determine whether the difference between the first signal and the second signal is within a set range:

[0024] If it is within the set range, the first signal or the second signal value is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured;

[0025] If it is not within the set range, the larger value of the first signal and the second signal is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured;

[0026] The concentration-voltage ratio K is the ratio of the pre-calibrated formaldehyde concentration to the corresponding formaldehyde infrared spectrum voltage value.

[0027] Preferably, when the wavelength band of one infrared light source cannot cover the range of 3.6um to 5.78um, two or more infrared light sources are used in combination so that the combined wavelength band can at least cover the range of 3.6um to 5.78um.

[0028] Preferably, the infrared light source is an LED lamp.

[0029] Furthermore, it also includes two amplifiers, which respectively amplify the voltage signals output by the two infrared detectors and then send them to the signal processor.

[0030] Preferably, the infrared detector is a thermocouple or a thermopile.

[0031] Preferably, the signal processor is implemented using a microprocessor unit, a DSP or a FPGA.

[0032] The present invention has the following beneficial effects:

[0033] The formaldehyde concentration detection method based on infrared absorption spectrum of the present invention detects the positions of two infrared absorption peaks of formaldehyde gas at the same time to detect the absorption of infrared light by formaldehyde, and finally calculates the formaldehyde concentration; since the gases in the atmosphere have their own characteristic absorption peaks, which will not overlap with the two absorption peaks of formaldehyde, the unaffected absorption peak can be selected as the data of the detection concentration, which can greatly reduce the influence of other gases and improve the detection accuracy of the formaldehyde concentration; in the present invention, the concentration voltage ratio coefficient k is calibrated in advance, and a reference channel is not set separately, so the detection process can be simplified;

[0034] The present invention adopts the method of formaldehyde absorbing specific light wavelengths, which is a physical method. Compared with the test paper and reagent detection method, this chemical method does not require reagents and can be measured in real time.

[0035] The formaldehyde concentration detection device based on infrared absorption spectrum of the present invention has long life of components such as light source, detector, electronic components, etc., which can extend the use time; and the device is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the infrared absorption spectrum of formaldehyde;

[0037] Figure 2 is the infrared absorption spectrum of carbon dioxide;

[0038] Figure 3 is the infrared absorption spectrum of water;

[0039] Figure 4 is the infrared absorption spectrum of sulfur dioxide;

[0040] Figure 5 It is a structural block diagram of the detection device of the present invention. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0042] The present invention adopts the method of infrared absorption spectroscopy to detect the absorption of infrared light by formaldehyde at the characteristic absorption peak of the formaldehyde infrared spectrum to calculate the formaldehyde concentration.

[0043] Compared with the general infrared absorption spectrum method, the present invention adopts a double absorption peak detection method: Figure 1 As shown in the figure, formaldehyde has strong absorption peaks at two specific wave numbers, located at 1730 cm -1 and 2800cm -1 location. Figures 2 to 4 In the figure are the absorption peaks of several common gases. The absorption spectra of these common gases do not have absorption peaks at the two absorption peaks of formaldehyde. Each gas affects the data at a certain peak at most. Even if it coincides with a certain absorption peak of formaldehyde, it will not coincide with both characteristic absorption peaks. Only formaldehyde has almost the same strong absorption at two positions, and the absorption coefficient is the same. Therefore, based on the above research results, the present invention calculates the formaldehyde concentration by detecting the absorption peaks of formaldehyde at the above two positions, specifically:

[0044] First, an infrared light source with a wavelength range covering the two absorption peaks of formaldehyde is used to irradiate the formaldehyde gas to be measured; then, a filter with a transmission wavelength of 3.6um is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the first signal; a filter with a transmission wavelength of 5.78um is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the second signal; it is determined whether the difference between the first signal and the second signal is within the set range:

[0045] If the two signals are equal or very similar, it means that other gases have almost no influence. Multiply any one of the two voltage signals by the concentration-voltage ratio K to get the concentration of the formaldehyde gas to be measured. If it is not within the set range, that is, the two voltage values ​​are one large and one small, the channel with a small value indicates that the absorption of other gases is superimposed on it, resulting in less light reaching the detector through this channel and a low value. At this time, multiply the larger voltage value by the concentration-voltage ratio K to get the concentration of the formaldehyde gas to be measured; by comparing the two channels, the influence of other gases can be greatly reduced, and the measured formaldehyde value is more accurate. Among them, the concentration-voltage ratio K can be achieved by prior calibration, that is: the concentration of the formaldehyde gas to be measured is known, and according to the above method, the voltage signal is detected to obtain the concentration-voltage ratio K; through multiple calibrations, an accurate ratio K can be obtained.

[0046] By measuring the values ​​of two absorption peaks at the same time and comparing the two values, the influence of other gases can be eliminated. In this way, the dual-channel infrared absorption spectroscopy method can detect formaldehyde concentration in real time and accurately. It solves the problem of aldehyde test paper and reagent detection methods, which have slow detection speed and cannot be repeated. It also solves the problem that electrochemical sensors are affected by multiple gases, making the measurement more accurate.

[0047] like Figure 5 As shown, the entire system consists of a light source, a gas chamber, two sets of filters, two sets of detectors, two sets of amplifiers, a signal processor, and a light source driving circuit.

[0048] The light source can be one or more infrared LEDs that provide light with a spectrum that covers the two absorption peaks. -1 and 2800cm -1 , that is, the wavelength range is 3.6um to 5.78um, then multiple LEDs with different luminous wavelengths can be used in combination to achieve the required wavelength coverage range. Of course, it is not limited to using LED lights, as long as the light source can provide this range of spectrum.

[0049] Filters 1 and 2 are designed to transmit only the wave number of 1730cm -1and 2800cm -1 . This can be achieved by controlling the coating thickness on the filter. The infrared detector can be a thermocouple or a thermopile. The amplifier can be a common integrated operational amplifier. Each channel can choose two-stage amplification. The signal processor can be a common microprocessor unit (MCU) chip, or DSP, FPGA, etc. The light emitted by the light source is absorbed by the gas to be measured and reaches filter 1 and filter 2, and can only pass through the wave number of 1730cm -1 and 2800cm -1 The two wave numbers of light are absorbed by detector 1 and detector 2 respectively, converted into electrical signals, and then amplified by amplifier 1 and amplifier 2 respectively, and then the signal processor (MCU) completes the analog-to-digital conversion through AD acquisition. The voltage values ​​of the two channels are obtained. The signal processor can obtain the formaldehyde concentration value through calculation according to the above method.

[0050] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A formaldehyde concentration detection method based on infrared absorption spectroscopy, characterized in that: include: An infrared light source with a wavelength range of at least 3.6um to 5.78um is used to irradiate the formaldehyde gas to be tested; A filter with a transmission wavelength of 3.6 μm is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the first signal; A filter with a transmission wavelength of 5.78 um is used to filter the infrared light absorbed by the formaldehyde gas to be measured, and the infrared light signal after filtering is converted into a voltage signal as the second signal; Determine whether the difference between the first signal and the second signal is within the set range: If it is within the set range, the first signal or the second signal value is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured; If it is not within the set range, the larger value of the first signal and the second signal is multiplied by the concentration voltage ratio K to obtain the concentration of the formaldehyde gas to be measured; The concentration-voltage ratio K is the ratio of the pre-calibrated formaldehyde concentration to the corresponding formaldehyde infrared spectrum voltage value.

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