The basic structure and detection principle of the new ozone detector
The ozone detector uses the principle of ultraviolet absorption method to generate ultraviolet light with a stable ultraviolet light source, and filters other wavelength ultraviolet light with a light filter, allowing only a wavelength of 253.7 nm to pass. After passing through the sample photosensor and passing through the ozone absorption cell, the sampled photoelectric sensor is reached. By comparing the electrical signals of the sample photosensor and the sampling photosensor, and then calculating the mathematical model, the ozone concentration can be obtained.
product description
We know that there is an ozone layer in the Earth's atmosphere. Scientists have found that the ozone layer can absorb ultraviolet light. Studies have shown that ozone has a maximum absorption coefficient only for ultraviolet light with a wavelength of 253.7 nm. At this wavelength, ultraviolet light will be attenuated by ozone, which is in line with Lanport-- Beer's law. This method has been used as an ozone standard analysis method in countries such as the United States. The ozone detector adopts the principle of ultraviolet absorption method, generates ultraviolet light by a stable ultraviolet light source, filters out other wavelength ultraviolet light with a light wave filter, and allows only a wavelength of 253.7 nm to pass. After passing through the sample photosensor and passing through the ozone absorption cell, the sampled photoelectric sensor is reached. By comparing the electrical signals of the sample photosensor and the sampling photosensor, and then calculating the mathematical model, the ozone concentration can be obtained.
basic structure
The detector is mainly composed of a low-pressure ultraviolet lamp, a light wave filter, an incident ultraviolet light reflector, an ozone absorption pool, a sample photoelectric sensor, a sampling photoelectric sensor, an output display, and a circuit component.
Application range
Ozone detectors are mainly used in ozone preparation workshops (ozone generators, ozone plants, etc.), chemical, petroleum, paper, textile, pharmaceutical and flavor and fragrance industries, water treatment, food and pharmaceutical sterilization workshops [1] and other occasions.
Detection principle
The detection principle of the ozone detector is semiconductor principle (E2V in the UK), electrochemical detection principle, and ultraviolet light principle. The main method introduced here is the third method, the ultraviolet light method.
Concentration calculation
The mathematical model of ozone concentration (such as Equation 1) is based on Lambert and Beer's law. In this ozone concentration calculation formula, as long as the sample current, the sampling current, and the ozone absorption tank distance are known, we can calculate the ozone concentration. Due to the limitation of the distance of the ozone absorption tank, the maximum ozone concentration can only be measured at 300 O3 g/m.
Circuit principle
The basic circuit consists of power supply, UV lamp control, UV light sample detection, UV light sampling detection, logarithmic amplifier Log100, analog output and display.
The core part of the circuit is to use the logarithmic amplifier Log100 to achieve a mathematical model of ozone concentration. The LOG100 is an integrated circuit with a 14-pin logarithm of two current or voltage ratios. The output current range of the amplifier is wide and can vary from 1nA to 1mA. The output error range does not exceed 0.1%. Basic wiring (Figure 1), output formula: Vout = VT × ln I0 / I (note: VT - - constant; Vout - output voltage).
The power supply section is mainly used to generate the high voltage power required by the UV lamp, and at the same time generate the +15V DC power required on the circuit board. The UV lamp control part mainly controls the current of the UV lamp within a constant allowable range. If it is too high or too low, it can be adjusted automatically. If the UV lamp life is not reached, a red light on the panel will light up, indicating that you should replace it. The new UV lamp is gone. The standard ultraviolet light detection and sampling ultraviolet light detection part is also a key part. The photoelectric sensor converts the ultraviolet light signal into a voltage signal, and then performs signal sorting and amplification through two operational amplifiers, and sends it to the LOG100 for calculation processing, and displays the output. The analog output 0~20mA is linear with the ozone concentration.
Calibration method
Calibration of the calibration instrument: The distribution of the ozone detectors produced by the ultraviolet light ozone detector is selected by 10 test points, and the error range is controlled within +1%.
Chemical titration: Internationally recognized chemical methods, namely potassium iodide, sodium thiosulfate titration to detect ozone concentration. We also distributed 10 test points and then compared them with the 10 points of the chemical titration test with an ozone detector. The error range was controlled within +1%. The principle of potassium iodide titration is to react with strong potassium iodine and potassium iodide to release iodine into the water, and the water will turn brown. (Reaction formula: O3+2KI+H2O O2+I2+KOH) The sodium thiosulfate standard was used to make the free iodine into sodium iodide, and the end point of the reaction was complete fading of water. (Reaction formula: I2+2Na2S2O3 2NaI+Na2S4O6)
Ozone concentration: C = (Ana × B × 2400) / V0 unit (mg / l)
(Note: Ana----sodium thiosulfate standard solution dosage ml; B---sodium thiosulfate standard solution concentration mol/l;
V0-----Ozone oxidation other sampling volume ml)
get conclusion
The ozone concentration detector developed in this paper adopts ultraviolet absorption method, single point light source, double optical path detection, small volume, high precision, good stability and continuous operation; its measurement range is wide, and the maximum measurement range is 300 O3 g/m. In addition, the detector also has a 0/4-20 mA analog output, which can be combined with an ozone generator and a PID regulator to form an ozone closed loop automatic control system.
It adopts new imported sensor and 32-bit low-power processor; the circuit adopts 4-layer wiring, which is stronger for weak signal and anti-interference; independent high-precision imported AD chip (some manufacturers use 2-layer circuit board and CPU internal for cost saving) The built-in AD function) is equipped with a unique signal processing algorithm, the measurement results are more accurate and stable; the 2.5-inch dot matrix display interface, the reading is intuitive and generous; the first-class process design brings a rock-solid quality. Can be applied to a variety of dangerous industrial sites; products are widely used in metallurgy, petroleum and petrochemical, municipal, chemical, bio-pharmaceutical, home environmental protection, school laboratories, automobile exhaust and other fields.
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