Study On High-Sensitivity Detection System Of Aromatic Hydrocarbons

With the large exploitation and wide application of oil,oil pollution of the water is becoming an increasingly serious problem,determining the content of oil in water by detecting Aromatic hydrocarbons has been widely recognized in the environment detecting.In this paper, we design a fluorescence-based high-sensitivity detection system, which can detect aromatic hydrocarbons in water, the testing process is quick and without other reagents, environmental protection, pollution-free, and high sensitivity.High sensitivity Aromatic hydrocarbons detection system is based of fluorescence analysis. This method uses certain substances in fluorescence under ultraviolet light and its intensity characteristics of the qualitative and quantitative material analysis,This method is known as fluorescence analysis.Through the bring about of Fluorescence and Lambert - Beer's law ,we can derived the relationship between the concentration of solution and the fluorescence intensity ,when the solution concentration is relatively low, they are linear. In the ultraviolet irradiation, only the aromatic substances will have wavelengths of 254nm fluorescence, so we can detect the fluorescence intensity of the 352nm wavelength to determine the content of aromatic hydrocarbons in water, which is the detection principle of the system.First of all, the working process of the system is to use deuterium lamp to radiate UV ,the UV then penetrates monochromatic of 253.7nm, and then irradiate color plate filled with a sample, fluorescent substances in the color plate produced fluorescence through the monochromatic of 352nm to filter out the rest of the fluorescence wavelength,the fluorescence come into the photomultiplier to be current signal. The current signal is transported to a amplifier circuit and is changed into voltage signal which is subsequently received by A/D converter of a MCU. The MCU is in charge of controlling the display, communication and data processing.The system uses C8051020F device as its MCU. The C8051F020 family utilizes Silicon Labs' proprietary CIP-51 microcontroller core. The CIP-51 employs a pipelined architecture that greatly increases its instruction throughput over the standard 8051 architecture. In a standard 8051, all instructions except for MUL and DIV take 12 or 24 system clock cycles to execute with a maximum system clock of 12-to-24 MHz. By contrast, the CIP-51 core executes 70% of its instructions in one or two system clock cycles, with only four instructions taking more than four system clock cycles.The most unique enhancement is the Digital Crossbar. The on-chip counter/timers, serial buses, HW interrupts, ADC Start of Conversion input, comparator outputs, and other digital signals in the controller can be configured to appear on the Port I/O pins specified in the Crossbar control registers.The C8051F020 has an on-chip 12-bit SAR ADC (ADC0) with a 9-channel input multiplexer and programmable gain amplifier. With a maximum throughput of 100 ksps, the ADC offers true 12-bit accuracy. The internal voltage reference circuit consists of a 1.2 V, 15 ppm/°C (typical) bandgap voltage reference generator and a gain-of-two output buffer amplifier. So using the internal voltage requires that the input current must be lower than 2.4V.The current signal emitted by the photomultiplier is so weak that the MCU can not detect exactly. The amplifier circuit contains a low-pass filter and an integrated operational amplifier ICL7650. The out voltage from the amplifier circuit and the signal ground are connected to the differential input ports of a instrumentation amplifier AD623 which is configured for unity gain (G = 1) in order to eliminate the common-mode interference.The system employs a LCM240128 made by XINHUAONG Corp. to display the result. The module contains LCD display, driving circuit, controlling module T6963C made by TOSHIBA,PCB main board ,RAM, and backup light.A 4*5 matrix keyboard is used and its nine controlling lines are all linked to the I/O ports of the MCU.The system has the capability of storing results by using a EEPROM AT24C512 even when it is not powered. The SMBus0 I/O interface between AT24C512 and MCU is a two-wire, bi-directional serial bus. It is compatible with the I2C serial bus.It is convenient for users to confirm and record the time by using a real time clock chip SD2303. In this system users could get or modify the time at any time. The interface between SD2303 to MCU is also a two-wire serial bus. A serial printer made by WEIDA is used. It makes that the result can not only be stored in the EEPROM, but also be printed out for people to check out.The system employs a portable switch power. Other internal voltages can be got by using some DC-DC converters.The system is programmed with C language under the development environment of KEIL C51μVision 2. Modularized programs consist of: multi-chinese character menu, displaying and modifying time, measuring and storing the result, querying and printing the history data and connecting to PC.To verify the reliability and stability of the instrument .System used market-saled 90 # diesel oil as a measurement object, used ultrasonic oscillator to mix diesel and water, the solution of different concentrations have been tested by system, The result is satisfied, the whole system is succeeded.The whole system performed well in the experiment. We should developed it and make more advantage. The instrument can also be improved into on-line measuring instruments.