CN102507507B - Device and method for detecting concentration of gas to be detected through temperature correction - Google Patents

Abstract

The invention discloses a device and method for detecting the concentration of a measured gas by using temperature correction, wherein the method comprises the following steps: an infrared beam with a wavelength of 2-12 μm is emitted from a heated radiation source, and frequency modulation is performed on the infrared beam ;Through the micro-flow detector to detect the infrared energy change of the infrared beam after the frequency modulation passes through the measured gas in the gas chamber, and convert it into an AC voltage signal; according to the influence of the change of the ambient temperature on the measurement results The voltage signal is corrected, and the corrected AC voltage signal is processed to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

Description

Device and method for detecting concentration of measured gas by temperature correction

technical field

The invention relates to the field of environmental monitoring, in particular to a device and method for detecting the concentration of a measured gas by using temperature correction.

Background technique

With the large-scale of my country's petrochemical, metallurgical, electric power and other industrial devices and the improvement of the overall technical equipment level, with the increasing pursuit of energy saving, quality improvement, pollution control and emission reduction, and safe production, the importance of online analytical instruments and Usage is increasing day by day. Infrared spectroscopy is one of the most rapidly developed analytical techniques for on-line analytical instruments in recent years, and has many advantages such as fast, efficient, and non-destructive.

However, the infrared gas analyzer has high requirements on the ambient temperature. The change of the ambient temperature directly affects the stability of the light source, the intensity of the infrared radiation, the density of the gas sample continuously flowing in the measurement gas chamber, and the normal operation of the detector, especially based on the micro flow rate. The infrared spectroscopy measurement method of the detector is more susceptible to the interference of the ambient temperature due to the thermal sensitivity of the sensitive element to measure the small gas flow change, thus affecting the measurement accuracy.

Contents of the invention

The invention provides a device and method for detecting the concentration of the gas to be measured by using temperature correction to reduce the influence of the ambient temperature on the gas detection concentration.

In order to achieve the above object, the present invention provides a device for detecting the concentration of the measured gas by temperature correction, which includes:

An infrared radiation source, which radiates infrared rays with a wavelength of 2-12 μm when heated;

The mirror is arranged in the shell of the infrared radiation source, and reflects the infrared rays into infrared beams;

The light cutting module turns the infrared beam into intermittent light for frequency modulation;

a measuring cell consisting of an analysis gas cell arranged in the optical path of the frequency-modulated infrared beam;

The micro-flow detector detects the energy change of the infrared beam after the frequency-modulated infrared beam passes through the measured gas in the gas chamber, and converts it into an AC voltage signal;

The concentration correction module corrects the AC voltage signal according to the influence of the change of ambient temperature on the measurement result, and processes the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

Preferably, the concentration correction module includes:

The fitting unit is used to detect multiple voltage values corresponding to the frequency-modulated infrared beam passing through the zero point gas under multiple ambient temperature values, and simulate multiple voltage values and corresponding multiple ambient temperature values according to the least square method Together, we get the formula:

y=Ax ² +Bx+C

Where x is the ambient temperature, y is the voltage value of the AC voltage signal, and A, B, and C are fitting coefficients;

The correction unit is used to correct the AC voltage signal according to the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}$

Among them, a1 is the voltage value of the AC voltage signal, a2 is the voltage value calculated by the formula y=Ax ² +Bx+C under the detection voltage signal corresponding to the ambient temperature, b1 is the expected voltage value after temperature correction, and b2 is normal The voltage value calculated by the formula y=Ax ² +Bx+C at a certain temperature within the measurement temperature range;

The circuit control unit is used to amplify, rectify and linearize the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

In order to achieve the above object, the present invention also provides a method for detecting the concentration of the measured gas by temperature correction, the method comprising the following steps:

Reflect the infrared rays with a wavelength of 2-12 μm emitted by the heated radiation source into infrared beams, and perform frequency modulation on the infrared beams;

The energy change of infrared rays after the frequency-modulated infrared beam passes through the gas to be measured in the analysis gas chamber is detected by a micro-flow detector, and converted into an AC voltage signal;

Correct the AC voltage signal according to the impact of the change of ambient temperature on the measurement result, and process the corrected AC voltage signal to obtain the concentration signal corresponding to the change of the measured gas concentration for display or control.

Preferably, in the above embodiment, the step of correcting the AC voltage signal according to the influence of the change of ambient temperature on the measurement result includes:

Detect multiple voltage values corresponding to the frequency-modulated infrared beam passing through the zero point gas under multiple ambient temperature values;

According to the least squares method, multiple voltage values and corresponding multiple ambient temperature values are fitted to obtain the formula:

y=Ax ² +Bx+C

Where x is the ambient temperature, y is the voltage value of the AC voltage signal, and A, B, and C are fitting coefficients;

Correct the AC voltage signal according to the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}$

Among them, a1 is the voltage value of the AC voltage signal, a2 is the voltage value calculated by the formula y=Ax ² +Bx+C under the detection voltage signal corresponding to the ambient temperature, b1 is the expected voltage value after temperature correction, and b2 is normal The voltage value calculated by the formula y=Ax ² +Bx+C at a certain temperature within the measurement temperature range.

Preferably, in the above embodiment, the step of processing the corrected AC voltage signal to obtain a concentration signal corresponding to the concentration change of the measured gas for display or control includes:

Amplify, rectify and linearize the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

In the above embodiment, after temperature compensation is performed on the detection results, the voltage values at the zero point and the end point after compensation are less affected by the ambient temperature, so that the finally measured concentration of the gas to be measured is more accurate and the effect of temperature compensation is achieved.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic diagram of the relationship between voltage value and temperature according to an embodiment of the present invention;

FIG. 2 is a flow chart of a method for detecting the concentration of a measured gas by temperature correction according to an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The infrared gas analyzer used to measure the concentration change of the measured gas is composed of an infrared analysis part and a circuit control part.

The light source, measuring cell and receiver are the three main components of the infrared analysis section.

Inside the light source component is a spiral infrared radiation source made of nickel-chromium wire. The heated radiation source emits infrared rays with a wavelength of 2-12 μm, which become infrared beams through the reflection of the mirror surface inside the radiation source housing. The light-cutting device turns the infrared light emitted by the light source into intermittent light, that is, modulates the frequency of the infrared light, so that the signal generated by the detector can become an AC signal, which is convenient for the amplifier to amplify, and can improve the response time characteristics of the detector.

The measuring cell consists of several analysis chambers arranged on the same housing. The length of the analysis gas chamber is based on the measuring range of the instrument to select the size of the measuring cell.

The receiver part adopts micro-flow detector, which is a new type of detector that uses the heat-sensitive characteristics of sensitive elements to measure small changes in gas flow. Its sensing elements are two miniature hot wire resistors and two other auxiliary resistors to form a Wheatstone bridge. The heating wire resistance is energized and heated to a certain temperature. When a gas flows through, part of the heat is taken away to cool the heating wire element, and the resistance changes, which is converted into an AC voltage signal corresponding to the change of the measured gas concentration through the bridge.

The circuit control part is mainly composed of several circuits such as microprocessor, display, analog/digital conversion, digital/analog conversion, temperature and alarm control.

The working principle of the infrared gas analyzer to measure the concentration change of the measured gas is as follows:

Infrared gas analyzers are made according to Beer's law. Assuming that the gas to be measured is an infinitely thin plane, and the infrared rays with an intensity of I ₀ penetrate it vertically, the amount of energy attenuation is:

dI=-Ikc·dl,

Integral: I=I ₀ e ^-kcl (Beer's law);

In the formula: I-radiation intensity absorbed by the medium;

I ₀ - the radiation intensity of infrared rays before passing through the medium;

k-absorption coefficient of the component to be analyzed to the radiation band;

c - the gas concentration of the component to be analyzed;

l-The length of the air chamber (thickness of the measured gas layer).

For a manufactured infrared gas analyzer, its measurement components have been determined, that is, the absorption coefficient k of the components to be analyzed to the radiation band is certain; the infrared light source has been determined, that is, the radiation intensity _I0 before the infrared rays pass through the medium is certain; The length l of the air chamber is constant. It can be seen from Beer's law that the concentration C of the component to be analyzed can be determined by measuring the attenuation I of the radiation energy.

The infrared gas analysis instrument is based on the non-spectral infrared absorption measurement method, that is, the principle of selective absorption of non-single element gas (or vapor) molecules in the infrared spectral range of 2 ~ 12um.

The parallel light beam modulated according to a certain frequency is emitted by an infrared light source. After passing through the analysis gas chamber, due to the absorption of infrared rays by the absorbing gas (measured gas) in the analysis gas chamber, the infrared energy change is converted into a voltage change through a micro flow detector. Furthermore, the concentration correction module corrects the AC voltage signal according to the influence of ambient temperature changes on the measurement results, and the corrected AC voltage signal is then processed by the electrical unit and control unit through amplification, rectification, and linearization. Output a signal corresponding to the change of the measured gas concentration for display or control.

For example, the concentration correction module includes:

The fitting unit is used to detect multiple voltage values corresponding to the frequency-modulated infrared beam passing through the zero point gas under multiple ambient temperature values, and simulate multiple voltage values and corresponding multiple ambient temperature values according to the least square method Together, we get the formula:

y=Ax ² +Bx+C;

Where x is the ambient temperature, y is the voltage value of the AC voltage signal, and A, B, and C are fitting coefficients;

The correction unit is used to correct the AC voltage signal according to the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}$

Among them, a1 is the voltage value of the AC voltage signal, a2 is the voltage value calculated by the formula y=Ax ² +Bx+C under the detection voltage signal corresponding to the ambient temperature, b1 is the expected voltage value after temperature correction, and b2 is normal The voltage value calculated by the formula y=Ax ² +Bx+C at a certain temperature within the measurement temperature range (for example, the normal measurement temperature range is 5-40°C, b2 can be the voltage value at 15°C);

The circuit control unit is used to amplify, rectify and linearize the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

FIG. 1 is a schematic diagram of the relationship between voltage and temperature according to an embodiment of the present invention; in FIG. 1 , the AD value represents the voltage value corresponding to the change of gas concentration. If the normal measurement temperature range is 5-40°C, put the infrared gas analysis instrument in a high and low temperature box and set 5°C, 15°C, 25°C, 35°C, 40°C (different temperatures can also be selected, but the normal measurement temperature The two ends of the range are fixed at 5°C and 40°C, and the other three points can take the average value between 5-40°C, such as 14°C, 23°C, and 32°C), and the zero-point gas is introduced to record the temperature corresponding to each temperature point. The original AD value and the detector temperature can be fitted by the least squares quadratic polynomial to obtain the voltage value fitting formula corresponding to the gas concentration change.

Data verification is carried out on the above temperature compensation method, and the verification results of zero point compensation are shown in Table 1.

Table 1

It can be seen from Table 1 that the original AD value of instrument A is greatly affected by the ambient temperature, but after temperature compensation, the zero point AD value after compensation is less affected by the ambient temperature, achieving the effect of temperature compensation.

The verification results of the temperature compensation data at the end point are shown in Table 2.

Table 2

It can be seen from Table 2 that the original AD value of instrument A is greatly affected by the ambient temperature, but after temperature compensation, the AD value of the end point after compensation is less affected by the ambient temperature, achieving the effect of temperature compensation.

Fig. 2 is a flow chart of a method for detecting the concentration of a measured gas by temperature correction according to an embodiment of the present invention; as shown in Fig. 2, the method includes the following steps:

S102, frequency modulating an infrared beam with a wavelength of 2-12 μm emitted by the heated radiation source;

S104, using a micro-flow detector to detect the energy change of infrared rays after the frequency-modulated infrared beam passes through the gas to be measured in the analysis gas chamber, and convert it into an AC voltage signal;

S106, correct the AC voltage signal according to the influence of the change of the ambient temperature on the measurement result, and process the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

For example, in the above embodiment, the step of correcting the AC voltage signal according to the influence of the change of ambient temperature on the measurement result includes:

Detect multiple voltage values corresponding to the frequency-modulated infrared beam passing through the zero point gas under multiple ambient temperature values;

According to the least squares method, multiple voltage values and corresponding multiple ambient temperature values are fitted to obtain the formula:

y=Ax ² +Bx+C

Where x is the ambient temperature, y is the voltage value of the AC voltage signal, and A, B, and C are fitting coefficients;

Correct the AC voltage signal according to the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 200000</span>}}$

Among them, a1 is the voltage value of the AC voltage signal, a2 is the voltage value calculated by the formula y=Ax ² +Bx+C under the detection voltage signal corresponding to the ambient temperature, b1 is the expected voltage value after temperature correction, and b2 is normal The voltage value calculated by the formula y=Ax ² +Bx+C at a certain temperature within the measurement temperature range. Fig. 1 shows a voltage value (AD value) fitting curve of an embodiment of the present invention.

For example, in the above embodiment, the step of processing the corrected AC voltage signal to obtain a concentration signal corresponding to the concentration change of the measured gas for display or control includes:

Amplify, rectify and linearize the corrected AC voltage signal to obtain a concentration signal corresponding to the change of the measured gas concentration for display or control.

From the verification results in Table 1 and Table 2, it can be seen that the original AD value of instrument A is greatly affected by the ambient temperature, but after temperature compensation, the AD values of the zero point and end point after compensation are less affected by the ambient temperature, thereby improving The accuracy of the concentration of the measured gas is improved, and the effect of temperature compensation is achieved.

Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of an embodiment, and the modules or processes in the accompanying drawing are not necessarily necessary for implementing the present invention.

Those of ordinary skill in the art can understand that: the modules in the device in the embodiment may be distributed in the device in the embodiment according to the description in the embodiment, or may be changed and located in one or more devices different from the embodiment. The modules in the above embodiments can be combined into one module, and can also be further divided into multiple sub-modules.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (3)

1. a device that utilizes the temperature correction to detect tested gas concentration is characterized in that, comprising:

Infrared origin gives off the infrared ray that wavelength is 2～12 μ m when it is heated;

Minute surface is arranged in the housing of infrared origin, is infrared beam with described infrared reflection;

Cut optical module, described infrared beam is become interrupted light, so that it is carried out frequency modulation (PFM);

Measuring cell is made up of the analysis air chamber that is arranged on the light path of warbled described infrared beam;

Ultrared energy variation behind the tested gas in micrometeor detecting device, the detection described analysis air chamber of described infrared beam process after frequency modulation (PFM), and convert thereof into ac voltage signal;

The concentration correction module, variation according to environment temperature is revised described ac voltage signal the influence of measurement result, and revised ac voltage signal handled obtains changing corresponding concentration signal for showing or control with described tested gas concentration;

Wherein, described concentration correction module comprises:

The match unit, for detection of under a plurality of ambient temperature value through the corresponding a plurality of magnitudes of voltage behind zero crossing gas of the described infrared beam after the frequency modulation (PFM), according to least square method described a plurality of magnitudes of voltage and corresponding a plurality of ambient temperature value are carried out match, obtain formula:

y=Ax ²+Bx+C

Wherein x is environment temperature, and y is the magnitude of voltage of ac voltage signal, and A, B, C are fitting coefficient;

Amending unit is used for according to following formula described ac voltage signal being revised:

$\frac{a2-a1}{a2-200000}=\frac{b2-b1}{b2-200000}$

Wherein, a1 is the magnitude of voltage of described ac voltage signal, and a2 is for detecting under the corresponding environment temperature of described voltage signal by formula y=Ax ²The magnitude of voltage that+Bx+C calculates, b1 are through the revised desired voltage values of excess temperature, and b2 is by formula y=Ax under the normal a certain temperature of measuring in the temperature range ²The magnitude of voltage that+Bx+C calculates;

Circuit control unit is used for revised ac voltage signal is amplified rectification and linearization, obtains changing corresponding concentration signal for showing or control with tested gas concentration.

2. a method of utilizing the temperature correction to detect tested gas concentration is characterized in that, may further comprise the steps:

The wavelength that heated radiation source is sent is that the infrared beam of 2～12 μ m carries out frequency modulation (PFM);

Detect described infrared beam ultrared energy variation behind the tested gas in the air chamber by analysis after frequency modulation (PFM) by the micrometeor detecting device, and convert thereof into ac voltage signal;

Variation according to environment temperature is revised described ac voltage signal the influence of measurement result, and revised ac voltage signal handled obtains changing corresponding concentration signal for showing or control with described tested gas concentration;

Wherein, according to the variation of environment temperature the influence of measurement result being revised step to described ac voltage signal comprises:

Detect under a plurality of ambient temperature value through the corresponding a plurality of magnitudes of voltage behind zero crossing gas of the described infrared beam after the frequency modulation (PFM);

According to least square method described a plurality of magnitudes of voltage and corresponding a plurality of ambient temperature value are carried out match, obtain formula:

y=Ax ²+Bx+C

Wherein x is environment temperature, and y is the magnitude of voltage of ac voltage signal, and A, B, C are fitting coefficient;

According to following formula described ac voltage signal is revised:

$\frac{a2-a1}{a2-200000}=\frac{b2-b1}{b2-200000}$

Wherein, a1 is the magnitude of voltage of described ac voltage signal, and a2 is for detecting under the corresponding environment temperature of described voltage signal by formula y=Ax ²The magnitude of voltage that+Bx+C calculates, b1 are through the revised desired voltage values of excess temperature, and b2 is by formula y=Ax under the normal a certain temperature of measuring in the temperature range ²The magnitude of voltage that+Bx+C calculates.

3. method according to claim 2 is characterized in that, revised ac voltage signal is handled obtaining the concentration signal corresponding with described tested gas concentration variation for demonstration or controlling step comprising:

Revised ac voltage signal is amplified rectification and linearization, obtain changing corresponding concentration signal for showing or control with tested gas concentration.

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