| With rapid development of the modern industry, the water is polluted more and more seriously. Ammoniac nitrogen is one of the most critical water pollutants. Over-standard ammoniac nitrogen in water may lead to many undesirable consequences, such as water eutrophication, the damage to ecological balance, degradation or even disappearance of lakes. Worse still, too much ammoniac nitrogen not only increases the costs of wastewater treatment, but also accelerates the corrosion and aging of treatment equipments, decreases the performance and work life of treatment equipments. Furthermore, if ammoniac nitrogen in drinking water is over standard, it will do harm to people's health, even causing serious consequences such as cancer and malformation. Consequently, Ammoniac nitrogen has become one of the most important evaluation indexes for water organic pollutants, and emphasized in water quality examination. Factories, enterprises and departments of environment should monitor the content of ammoniac nitrogen, investigate the pollution and self-cleaning condition in water in real time. So that proper measures protecting environment and ensuring water quality can be adopted accordingly.At present, the instruments on sale for detecting the content of Ammoniac nitrogen major base on titration method, Ammonia Chloride Ion-Selective Electrode method, Ammonia gas-sensing Electrode method, salicylic acid colorimetric and nessler reagent colorimetric. These kinds of instruments, complicated in use, are generally used for detecting in laboratory. Moreover, high costs in manufacture make them expensive and hard to expand. This paper designs a portable instrument for ammoniac nitrogen detection, with low price, easy to operate, and can detect the ammoniac nitrogen content in water quickly.The portable instrument this paper designed for ammoniac nitrogen detection using nessler reagent spectrophotometer method. The theoretical basis for quantitative detecting is Lambert-Beer's Law, and accordingly, we calculate the content of Ammonia Chloride according to colored absorbance of the sample. We will briefly introduce this instrument from hardware design and software design as below.1. Hardware DesignA 32-bit ARM7 MCU LPC2136, made by Philips, is used in this instrument in order to process the data and control signals. LPC2136 has many advantages, such as high speed in processing data, plentiful resources in chip, small package and low power, which suiting our design perfectly.The part of photoelectric detection use 430nm LED as detecting light source. Compared with other monochrome source system, this kind of LED has many advantages, such as low working voltage and working current, uniform and steady light, quick response, small volume, long work life, low prices and so on. Besides, the intensity of the light can be set manually, which benefits instrument's calibration and maintenance. Also, Light frequency converter TSL230 is used to detect the light intensity after the colorimetric bottle, which reduces the complexity of the circuit, lowers the costs, and increases stability of the system.The human-computer module is mainly composed of lattice LCD and four keys. Through the rational design, the four keys may accomplish all kinds of input operations, the 240 by 128 LCD may display a great deal of information intuitively. The circuit structure is simple while satisfy the demand completely. Otherwise, an interface for micro printer is included in this instrument as well. In this way, a printer can be easily used through this interface in the case when some data needs to be printed, which is convenient for users, yet does not affect the portable property of the instrument.In order to ensure the safety of working curves, measuring record, user's set and time information after system power-down, a 64KB E2PROM chip and real-time clock chip is used in this instrument.In the part of power supply management, a 720mAh in volume and 7.2V in voltage Li iron battery is used. Accordingly, charging circuit, voltage transformation circuit, and charge testing circuit which are stable, reliable and low-power is also used. Besides, a soft-switching circuit is used to prevent power consuming caused by user's misoperation, a turn-on operation which maintains more than three seconds is required to turn on this instrument.2. Software DesignThis instrument adopts the more accurate multi-cycle synchronous method to detect the output frequency of TSL230 to avoid the counting error of direct measuring method. Plus, this instrument adopts fitting method to determine the working curve, and reduce the curve fluctuation from single measuring error. Furthermore, compared with that from interpolation method, the function from fitting method is simpler in form, and more convenient for calculating.The concept of modularization is carried out all through software design. The code of each module is written independently, and the interfaces are easy to use. Thus the complexity is lowered, development cycle is short, and the whole program is easy to be maintained and extended.In the driver procedure part of LCD display and micro-printer output, the ordinary method of writing user-define function is dropped. By using the way of redirecting the function fputc() in stdio function library of ARM ADS1.2, it is very convenient to use printf() function to give an output after setting relative parameters. Not only very easy to use it is, but also very easy to transplant the procedure.The software of human-computer interface adopts level-division menu design, thus, it is very easy to write the code, so does the modification. The design of interface is reasonable and concise, with perfect operation tips, and this method is customized while the design is more humanizing.Besides, for the purpose of enhance system safety, password protection and danger alarming is introduced. Generally speaking, the hardware of this system is stable and reliable, also low-power, and the software of this system has clear level, explicit structured, and is easy to extend. Thus, the instrument is easy to operate. After detecting a group of standard solution which has limited ammoniac nitrogen, it is found that the maximum relative standard deviation is less than 5%. And therefore, this instrument matches the design demands, and can meet the needs of fast detecting on site. The detecting method of this instrument, spectrophotometer method, is an ordinary chemical detecting method, which can be used to detect many other parameters in water, such as content of chlorine dioxide, fluoride, sodium hypochlorite, calcium, manganese, hexavalent chromium and so on. The difference is the reagent for coloring and the wavelength of the light source. While the instruments are basically identical in hardware structure .As a result, this design has very high reference value for other similar detecting instruments. Furthermore, the serial ports for communication have been reserved, by which the instrument can communicate with PC or wireless instrument network, and there is a large space for deeper development and broad application prospects on this instrument. |
PDF Full Text Request