Study On The Impact Of Gas Flow Rate And Humidity On Gas Sensors And Electronic Nose

Electronic nose is an instruments to identify the concentration and components of the odor by imitating the mechanism of animals'sense of smell. Electonic noses are one of the most focused area in gas detection field since they have the advantages of low cost, small, and high sensitivity. However, the electonic noses are sensitive to the surroundings which restrained their application.It was found that dynamic testing results and static test results of the electronic nose are quite different, and the main differences between the two methods are the gas flow velocity and humidity. In this paper, the influence of the flow velocity and relative humidity on the gas sensor response are studied by experimental testing, flow simulation and analysis of the sensing mechanism.and the compensation methods of the electronic nose system are givenFirst of all, a test chamber which can produce an uniform and stable airflow was designed for measuring the impact of flow rate on the response of semiconductor gas sensors. The flow field in the chamber was analysed using fluid simulation software Fluent, and thereby the position of the gas sensor in the chamber was determined and the range of the air flow rate was calculated. The experimental test system is a dynamic system based on the standard gases and mass flow controller, an automated test software is designed with Labview to control the gas flow rate and make a real-time acquisition, display and storage of the sensor signal. During a test, air and 0.4% ethylene was injected into the test chamber alternately, at flow range of 4.2cm/s～84.9cm/s. The baseline voltage, response voltage, response time and recovery time, sensitivity and other parameters of three kinds of semiconductor sensors (TGS2610, TGS2620 and MP4) were measured. Results show that the flow velocity definitely influence the baseline voltage and response voltage of the gas sensors but the degree of influence is different. All the three gas sensors'response time and recovery time decrease with the flow rate increasing, while their response sensitivity are slightly increased with the increasing of the flow velocity. These measurement results were discussed with the simulation results of the flow field and the sensing mechanisms.Secondly, to study the humidity impact on the response of semiconductor gas sensors, a humidity pathway was introduced in the experimental system to generate different humidity of the gases, and the temperature and humidity of the chamber were measured with SHT11. The impact of the humidity on the TGS2610, TGS2620 and TGS813 were measured. Results show that both the baseline and the response signal of the gas sensors are affected greatly by humidity, and the sensitive mechanism was discussed.The impact of flow velocity on the gas sensors can be minimized by using a stable gas suction device, while the humidity of the gas is unavoidable, thus a compensation of humidity to the electronic nose is needed. Adding the humidity sensor signal to the gas sensor array signal, using principal component analysis and BP neural network method for the quantitative identification of methane and ethylene, the results show that the method well compensated the measurement error caused by humidity, and the recognition effect electronic nose was obviously improved.