The Research And Realization Of The Systerm Of Ammonia Sensor Based On The Polyaniline And Polystyrene Sulfonic Acid Assembling Composite Film

As an important chemical material, ammonia has an irreplaceable role in today’s production and life, at the same time ammonia also is a toxic, flammable and explosive gases, Ammonia is a recognized source of stress in the animal husbandry, the high concentrations of ammonia would take directly harm to animal, so monitoring the concentration of the ammonia in the environment is becoming more and more important. But the traditional inorganic semiconductor ammonia gas sensor often has a poor selectivity, large volume and high temperature, and the sensor’s time of response is too long. Therefore, the fast response, small size, low power consumption and having a stable outputting has become an important direction of the development of the ammonia sensor.Polyaniline is a kind of polymer material which has the advantages of simple preparation, stable property and kinds of different structures and can be doped. As the intrinsic polyaniline be doped by the proton acid, it can be turned from an insulator to a conductor with good electrical conductivity. In this paper, we analyze the three conductive models of the doped polyaniline from the sight of the structure and the properties of the polyaniline. Through the way of chemical oxidative polymerization synthesis, we got the conductive polyaniline which is doped from the aniline. And the whole production process is simple, the resulting solution was well dispersed.By the method of composite assembly, we got some assembly of polyaniline and polystyrene sulfonic acid composite films having a different number of layers on the interdigital electrode by looking the doped polyaniline and polystyrene sulfonate which has the molecular weight and simultaneously with a large number of charged groups as polyelectrolyte material. Compare the sensitive film which is obtained by composite assembly and the drops of pure polyaniline, we found that the sensitive film which was obtained by composite assembly haven a better coverage and uniformity. At the same time, we also studied on the response characteristics of the sensors which with different composite film numbers to ammonia. The results shown that the ammonia concentration in the range of 30ppm to 300ppm, the sensors all haven an excellent response and recovery characteristics to ammonia, the sensors also showed a good reproducibility, on the same time the sensors also haven a very good linearity and the good selectivity to ammonia.Taken the ammonia gas sensor and FPGA as the core to build a sensor system which can detect the ammonia concentration in the surrounding environment in real time.In the article we made the resistance variation characteristic of the sensor when the ammonia concentration changes manifested conversion changes become square wave frequency based on the square wave generating circuit.And the send the signal to a signal shaping circuit for shaping, finally sent it into the FPGA for countting frequency processing. At the same time, we alse introduced the whole peripheral hardware circuit of the sensor system,at last we introduced the Nios Ⅱ building sensor system based on the software part and analysed it’s iplementation process.By the experimental device which was introduced in the paper, we got the relationship between the ammonia concentration and the frequency. We used the Matlab fitting the relationship between them and their function curves. At the same time implemented the calculation of ammonia concentration in the surrounding environment in the Nios software system. Finally, by the experiment of the whole sensor system we analysed the reason and the error measurement between the measured value and the actual value and we also raised the place which is need to improve.