Study On The Infrared Oils Analysis System

1. The purpose of the studyBody of water refers to surface water, groundwater, and water, suspended solids, sediments and aquatic organisms collectively. With industrial development, oil-bearing wastewater pollution of water bodies becomes more serious. Biochemical oxygen demand due to the high mineral oil, oxidized oil per kilogram of approximately 3.3 million milligrams of oxygen, while the oil floating on the water of oxygen in the air will prevent re-entering the water body, and thus the oil-polluted waters, easily cause a water body of oxygen, affecting fish and other aquatic organisms to survive, resulting in lower yield and quality of aquatic products. After water body has contaminated by Petroleum , not only its sensory state (color, smell) changes, but its value are affected, aquatic resources and human health is seriously jeopardized.In the world in many countries of the wastewater emission concentration of oil has made rules and restrictions, China's "Integrated Wastewater Discharge Standard" (GB8978-1996) in the oil of the emission concentration limits I, II, III emission standards were 5,10,20mg/L.Therefore, the control and prevention of water pollution are important issues related to people's livelihood. The requirements of environmental monitoring techniques are also increasingly systematic and standardized. Substances other than oil in water detection technology to carry out the research, both to ensure that national scientific development of water resources development and utilization planning, but also to protect water security, food security, ecological security of the urgent needs.2. Principle of Infrared Oils Analysis SystemWhen the infrared light beam irradiation a substance, the substance will absorb part of the light elements, and its transformation into molecular vibrational energy and rotational energy. Meet the following requirements when the molecule absorbs light energy and electric dipole moment change occurs, it will transition resulting spectrum. DE =E2 -E1=hn 2.1Among them, E1 and E 2 are molecule and finally the initial energy state energy state energy respectively,h is Planck constant,Its value is 6. 624′10-27s,n is The frequency of light absorbed。The amount of light energy is absorbed by the Lambert - Beer law to determine。According to Lambert - Beer law, through the medium thickness l is the intensity after the I=I0exp(-αCl) 2.2 Whereαis the absorption coefficient. Therefore, as long as the measured I0 the incident light and outgoing light I, will be able to calculate the concentration of C. C = a1llnT1 2.3 T=I/I0 is transmittance.The oil substances contain CH3-,-CH2-, =CH-, and other groups. Groups of their characteristic absorption peaks of 2960cm-1, 2930cm-1, 3030cm-1. Therefore, by measuring the light transmission rate of this position, we can calculate the concentration of substances other than oil.The use of infrared spectrophotometry to detect substances other than oil bodies of water, due to the above wavelengths near the absorption of water would interfere with measurement results, so we choose in this band almost no absorption of carbon tetrachloride (CCl4) solution as a extractant, by measuring the oil concentration in the carbon tetrachloride solution, and finally converted a water content of the oil copies.3. System ComponentsThis system mainly consists of optical systems, electrical systems, data analysis and processing system has three major components. Working schematic diagram shown in Figure 3.1. Issued by the infrared light source, modulated by the modulator into the optical communication frequency of 480Hz signal, so that the modulated light can come through the analyte solution, respectively, and reference solution, the outgoing light through the filter, so samples were obtained and the light at the end of the sample Strong I and I0.I and I0 exposure to the photoconductive detector into electrical signals, because the incident light into a strong modulated AC signal, it is also a photoelectric conversion signals after the AC signal, it can be subjected to pre-amplifier distortion amplification processing, amplified signal, after being collected by the A / D conversion, the original analog signals into digital signals the computer can recognize into the SCM system for processing.After the data into the microcomputer through a series of calculations to be measured, displayed, if necessary, can also choose to print or upload to PC computer for further processing and analysis.4. Experiment and Performance4.1 Determination of absorption coefficientBecause certain external conditions (temperature, pressure), the absorption coefficient of the same material in a certain wavelength has a fixed value, not with its concentration varies, so we can first by measuring a known concentration of standard samples to calibration value. Measured through multiple light intensity I0 background and signal light intensity I, obtained a series of values, at last the arithmetic average of 1a a is taken as the absorption coefficient a's value,a's error is expressed by the average standard deviation:d i。Table 4.1 for the 10 measurements obtained through the results. Table 4.1 Experimental Determination Measurements a Absorption coefficient (l mg-1 cm-1) a Arithmetic mean 0.01999 d 0.000044.2 Determination of sample concentrationThe system chose concentration of 0.5ppm, 1ppm, 2ppm, 5ppm, 10ppm samples to experiment, experimental results shown in Table 4.2.In order to facilitate analysis and comparison, according to Table 4.2 draw a sample test curve shown in Figure 4.1.4.3 Measurements amendmentFrom the above chart we can see the results with the standard between the values measured there are some errors, the following test results, we make the following amendments.Figure 4.2 for PbSe spectral response curve, can be seen, PbSe detector response and environmental temperature, which makes this the end of the signal and sample signal conductance value changes with temperature changes, thereby to bring the concentration of error of measurement results.Method of amendment is the absorption coefficient at different temperatures for calibration. The results of the calibration data stored in memory at different temperatures, choose a different value calculated.Table 4.3, Table 4.4 at different temperatures and different time (time interval of 5 minutes) obtained measurements. The measured concentration of 2ppm sample of the standard samples. Based on the above pairs of values at different temperatures to recalibration, and then choose to respond to the value of the ambient temperature calculated to be revised measurement results are as follows.Based on the table data we can see that the results of the revised error can be controlled within 4%, indicating the system has high accuracy, to meet the national standard.4.4 System Error CausesRevised after the measurement results significantly improved, but still there is a certain margin of error, then the error is how to generate it? Specifically, we analyze below.(1) PbSe detector in the course of their work there is a certain temperature drift and time drift is a measure of the value there is a certain error.(2) The application of quantitative determination of Beer's law, there are some errors, especially the concentration is too high or too low will cause the transmission rate is too low or too high.(3) Testing of this system is 3.5±0.25μm range of light intensity within the segment. This section includes methyl (CH3-), methylene (-CH2-), aromatics (= CH-) groups such as the characteristic absorption peaks, but because of different concentrations of oil-like substance, the group's share of the ratio may be different, even if the concentration of the same two samples may also happen. Calibration we measured the value is actually a certain percentage of each group in cases where integrated value. That is when the proportion of each group, once changed, the value will change accordingly, thus giving a greater error of measurement caused.(4) As the calculation of the number of the process, thanks to a larger memory space occupied by floating-point operations, so the calculation of its Taylor expansion, and only by taking the first three, this also brings a certain measurement error.(5) samples during transportation and operation, will be human-induced changes in concentration.5. ConclusionOil analysis techniques were developed over the years, professional and technical personnel in the countries around the world continued to explore and by studying, under a variety of measurement methods and measuring instruments one after another, while the infrared photometry of its high accuracy, repeatability is good, the scope of application wide, the advantages of simple operation have been the world consensus in China, in 1996 determined to be oil-like substance by infrared spectrophotometry determination of the standard method. After nearly 10 years of development, especially in recent years, liquid-core waveguide infrared absorption technique, spectral techniques have been bold retina after application, our oil-infrared measurement technology has reached the world advanced level, and even a leading position.In this paper were developed infrared oil analysis system, drawing on the results of previous studies, through the transformation of light road and circuit optimization of the system, allowing the system to the miniaturization of a step forward in the direction of development. At the same time using a highly integrated microcontroller and peripheral devices, a higher degree of intelligent systems, operation is easy.At the same time, from the measurement results, there is still a margin of error, according to the previous causes of error analysis, to make a few improvements to the system program, hoping to reduce errors, improve accuracy and stability.(1) The selected cooling temperature of the infrared detector with a certain period of time before preheating, reduce temperature drift and time drift effects.(2) concentration is too high or too low, the appropriate amendments to the errors.(3) system, optical design, adopt a more high-performance narrowband filters, each filter out three of the center wavelength of the intrinsic absorption, or increase the spectral components in the system will start outgoing light according to wavelength were measured three of the sign at the light absorption intensity to the concentration of the calculation.(4) To minimize the calculation error.(5) strict operational processes to minimize human error.