Formaldehyde Portable Detector Study

Construction materials which were made by many stuffs come into peoples` house with the development of level of life and request of higher quality of life. And formaldehyde is considered as the deputation of chemic matters that make air pollution in the house. Formaldehyde is one of most common materials used in industry. Many reasons contribute to the pollution that made by formaldehyde, such as: ornament materials, new furniture, cement wall mixed with alkali and so on. With the development of level of life and request of higher quality of life, people bring forward higher standard for inspecting the consistence of formaldehyde, especially, for inspecting the low consistence of formaldehyde.Presently common formaldehyde tester on the market is based on technique called test paper photoelectric photometer, that is: medicament contained in the test paper will occur chemic reaction when formaldehyde contacts with the test paper that dipped in chromogenic reagent, the color of test paper will turn from white to yellow. The degree of color changed reflects level of formaldehyde content in tested air. In this way we can analyze consistency of formaldehyde only by eyes, so the most disadvantage of this method is low precision.A portable formaldehyde tester that base on Electrochemistry transducer will be introduced in this dissertation.Hardware, electrochemistry transducer is used. When formaldehyde diffuses into the interior of the sensor, it will act with the liquid in the sensor, then makes a faintness current signal, the current signal goes into a circuit and switches into a voltage signal, the voltage signal will goes thought a circuit which is used for dispose signal before put it into the A/D converter. The digital signal will be collected onto STC89C51 begin signal disposal. Communications with STC89C51 will be implemented by using key-press and LCD.On software side for reduce energy consume of the system, shorten runtime of the CPU, When the apparatus has not been operated for a while, the system will close a part of chip and makes the MCU repose in order to reduce the using up of power.With regard to dependability of operation, the task appends code protection function in order to prevent the sample point from modification and adds the function of boot-strap with a button for the sake of avoiding the error of boot-strap. At the meanwhile, the system also has a function of voltage detecting and a function of hinge by time in order to avoid excess discharge of battery.The design has some characteristics. For example, simple structure of circuit,convenience of operation,low power using up,stabilization of system.