With the progress of human society and the development of science and technology, people's living standard has been a rapid increase, industrial production scale is also rapidly expanding, but at the same time lead to a doubling of carbon dioxide emissions, such as the greenhouse effect, the degree of acceleration of desertification, seriously affected and to destroy human life environment.
In addition, carbon dioxide is the main raw materials of crop photosynthesis, its content is appropriate or not directly affect crop growth. In recent years, as the people's awareness of environmental protection, science and technology progress, how to quickly detect carbon dioxide levels, reducing carbon dioxide emissions, has become an insight in the different levels of Government and the wider issues of particular concern, the study and design of the CO2 detection circuit is very important.The current method of detecting carbon dioxide mainly chemical, electrochemical, gas chromatography, capacity, titration, etc., which are prevailing prices, universal issues such as sexual difference, and the measurement accuracy is also low.
And sensor method has a safe and reliable, fast and direct reading, continuous monitoring, etc. Current detection of carbon dioxide sensor mainly solid electrolyte formula, barium titanate mixed oxide capacitor, electrical conductivity changes-thick film type and so on, these sensors exist on gas selective, prone to false positives, require frequent calibration, life is short, and so on. And infrared absorption measurement of carbon dioxide sensor has a wide range, high sensitivity, faster response time, selective, and strong anti-interference ability, etc. For this reason this design uses infrared absorption of carbon dioxide sensor, the entire circuit design simplicity and easy to use, fast, low-cost direct-reading.1 detection circuit works
1.1 infrared absorption of CO2 gas sensor works 1 2600 s
Infrared absorption of CO2 gas sensor is based on gas absorption with the substance of the differences in principle.
Chemical structure of different gas molecules, on different wavelengths of infrared radiation absorption degree is different, so different wavelengths of infrared radiation, exposure to sample material, certain wavelengths of radiation energy is absorbed by the sample material selection, resulting in weaker infrared absorption, so when you know that some substances by infrared absorption spectrum, they can get the material in the infrared portion of the absorption peak. Same substance concentration, in the same absorption peak position have different absorption strength, absorption is proportional to the intensity and concentration. Therefore by detecting gas on optical wavelength and intensity of impact, we can determine the concentration of gas.According to Bill Lambert's law, the output light intensity, the input light intensity and the relationship between the gas concentration is:
(1)
-Molecular absorption coefficient for Moore; C to be measured gas concentrations; L-light and gases of length (sensor length).
The type to transform must:(2)
By detection of related data you can know the concentration of gas.
Figure 1 the structure of carbon dioxide sensor probe
Infrared carbon dioxide sensor probe structure as shown in Figure 1.
By infrared light source, measuring Chamber, adjustable interference filter, optical detectors, optical modulation circuit, amplifier system, etc. Infrared light source using nickel wire, power heated may issue 3 ~ 10 μm IR, containing 4.26 μ m CO2 gas strong absorption peak. In the gas chamber, carbon dioxide absorption light sources emit specific wavelengths of light, the detector detection you can display the carbon dioxide absorption of infrared radiation. Interference filter is adjustable, can change their accommodation through light wave band, thus changing the detector detects the signal strength. Infrared detectors for film capacitors, absorption of infrared energy, gas temperature rise, leading to increased pressure, indoor capacitances distance between the two poles will change, capacitance values change. CO2 gas concentration, capacitance value changes also.1.2 detection circuit design principles
Figure 2 measuring circuit diagrams
Detection circuit design principle diagram shown in Figure 2.
Detection circuit by infrared CO2 sensor, digital filtering circuit, amplifier, steady flow circuit, single-chip system, temperature compensation, etc.
The basic principles of design are infrared CO2 sensor will detect the concentration of carbon dioxide gas is converted into the appropriate signal, the output of the signal after filtering, zoom in, respectively, enters into a single-chip system, and the temperature and pressure compensation processing, output from SCM system to display device display measurement values.1.3 detection circuit design
Figure 3 CO2 detection circuit diagram
Follow these design principles, design of the CO2 detection circuit shown in Figure 3.
The working principle is first and foremost by infrared sensor will detect the concentration of carbon dioxide gas and converted into electrical signals, filter circuit extraction signal and output to the amplifier circuit, through the single-chip system output, then after processing by the Fed show circuit 74AC138 to achieve CO2 concentration detection.Circuit from R1, R2, R3, R4, C1, C2 and amplifier filter circuits], [2, in the circuit is introduced and negative feedback, the introduction of positive feedback.
When the signal frequency tends to zero, as C1 reactance tends to infinity, and positive feedback is weak; when the signal frequency tends to infinity, C2 reactance tends to zero. This ensures that when the signal frequency tends to zero and infinity any value between, filter circuit can normally extract the appropriate signal.Filtering circuit after amplifying circuit, its function is to filter the output of the signal amplification to a certain extent, so that
Driver load. R6 and C4 series constitute correction network used to conduct phase compensation circuit.SCM system is mainly composed of MC14433 and 8031, MC14433 is a double integral chip A/D conversion, and how 8031 figure.
MC14433 's conversion of P1.0-P1.3 Q-Q received 8031, gated output pulse DS1-DS4 received the P1.4-P1.7 8031. The conversion result flag EOC, on the one hand followed to update conversion control signal input line, on the other hand next to DU 8031 interrupt input line INT1, SCM can use interrupt mode into the A/D conversion results, or you can use query mode. The final result into 74AC138 and driving the digital display specific numerical [3] [4].Inspection handler process diagram shown in Figure 4.
Using MCS series Assembly language programming, s 5 Eclipse because of hardware design that makes the whole system can work in the query, you can work in interrupt management.3 closing
The design has been successfully applied to Yan'an Prefecture flower Demonstration Garden, runs good effect.
Practice shows that this detection circuit is simple, numerical display, small portable, very intuitive, continuous and rapid detection, may at any time to detect various occasions for indoor and outdoor concentrations of carbon dioxide gas.
Figure 4 test handler flowchart
This circuit design simple, cheap, ubiquitous, overcome the need for frequent calibration, useful life is shorter, less expensive, and so on.
Reference documents:
[1] Kui Xuemei et al. infrared absorption of CO2 gas sensor design [J]. sensor technology, 2005, 8: 62-64.
[2] poetry white, Huacheng Ying. analog electronics [M] Beijing: higher education press, 2001.
[3] the army through cattle, peak traffic based on microcontroller-system controller [J]. a micro-computer information, 2004, 8: 21-22.
[4] NIE Yi, NIE fai. microprocessor control system for greenhouse plants [J]. a micro-computer information, 2002, 8: 36-37.
[5] Xue Jun Yi, zhangyanbin .MC551/96 series single-chip microcomputers and application [M]-Xi'an Jiaotong University Press, 1990.
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