The Development Of Handy Gas-sensitive Sensor

In recent years, with the exploitation andpopularization of Natural gas, the disclosure of Natural gasnot only leads to the serious economic loss of the countrybut also brings about the great menace of people's safety.It is very necessary to determine and monitor theconcentration change of the Natural gas. The informationtechnique substitutes for the Mimic technique because of therapid development and the improvement of LSI. So many kindsof devices and products will appear in our lives. Furthermore,the stability of resistor-modeling gas sensor is upgradedand the cost is reduced with the progress of modernelectronic industry. It is probable for the usage ofbrainpower-modeling gas sensor against this background.In this paper, the resistor-modeling gas sensor is usedto check the natural gas. The N-semiconductor gas sensor ismainly made up of semiconductor metal oxide ceramic gassensor. A kind of metal oxide film (such as SnO2, ZnO, andFe2O5, TiO2 etc) is made into the resistor. The value ofresistor will change with the concentration of the gas. Thegas molecules on the film surface may cause reductionreaction which results to the change of the conduct ratio.In order to remove the gas molecules, new types of materialsmust be exploited including compound metal oxides, mixedmetal oxides .The study and exploitation of these materialsextremely raises the characteristics and the usage range ofthe gas sensor. Besides, The sensitivity and response timeof elements are effectively raised by adding precious metal(such as Pt, Pdand rr etc) to the semiconductor because theprecious metal can decrease the chemisorption activationenergy of the examined gas. Furthermore, different catalyticagents may lead to different chemisorption model, so it isselective to the catalytic agents. With the above-mentioned,the metal oxide gas sensor made by film technique andsuperfilm technique has high-sensitivity (reach 10-9magnitude), high-stability and portable, easy-integration.Based on the fact of the market, the design principleof the system is to try to decrease the cost in the reliableworking condition. The main work includes several aspects:(1) JE-SGS-(I) resistor-modeling CH4 gas sensor is used andsupplied by constant electronic current. (2) The natural gasis sampled and examined by the sensor, and the dataprocessing and analyzing are carried out by the hardware andthe soft ware designed, then the data signals which aretransformed from the Mimic signals are directly displayedon the screen. (3) the system is examined and adjusted.The single CMOS Chip (AT89C2051) in the series of MCS-51of ATMEL Company is adopted to process the datum and controlthe system. The whole system is divided into two parts: thehardware and the software. The hardware is made up of fourparts: data-collection, A/D transform, single CMOS Chip andLCD-Display. With the concentration change of natural gas,we will transform the value of resistor of N-semiconductorgas sensor to the voltage between the resistor via peripheralcircuits, then after voltage is transformed to frequency viaV/F transformer, we will send the result to the single CMOSChip (AT89C2051),the data are processed via the single CMOSChip ,finally display the natural gas concentration underthe control of the single CMOS Chip. Though the system isthe device which is used to check the natural gasconcentration, we use the way of linearization to processthe data, then send to the LCD-Display. Besides that thesystem has the functions of displaying when low-voltage ,alerting and displaying when exceeding the normal level.The characteristics of the system are simple-electric circle,high-dependability, low-cost and easy-operation. Thesoftware is mainly made up of three parts: data-collectingson-program, data-processing son-program and displayingpart. The software is made with file languages of MCS-51series and the whole programs are fixed in AT89C2051. Thedata processed by the single CMOS Chip is binary and not easyto display, so the binary data must be informed into decadedata. Finally, the value of gas concentration is displayedby LCD.The resistor-modeling CH4 gas sensor (JE-SGS-(I)) isused in this system. The resistor value of N-semiconductorgas sensor will change when the natural gas containing CH4is absorbed by the surface of JE-SGS-(I) gas sensor. Theresistor value will decrease with the increase of the gasconcentration. In order to accelerate the absorption andremoving of the checked gas, the gas sensor must be heatedwhen it works. Different heated temperature has differentselective effect for different gas. Heated temperature alsoinfluences the output sensitivity of the element. After thegas sensor reaches the steady state, the checked gas (suchas H, CO,SO2 etc) is absorbed on the surface of the elementand the resistor value decreased. The concentration ofeasy-burning gas is much greater;the resistor value is muchsmaller. So we can realize the checking of the gas. Fordifferent organic gas, the electronic current of the heatedwire has different range. The range is 100mA-65mA. In thissystem, for CH4 gas, the current is about 145mA.Based on theabove-mentioned, we choice the constant electronic currentto heat he wire.In repeated tests, there appear some disadvantages onthe gas sensor, so we need continuously explore the newmethods and exploit the new materials to improve thecharacteristics of gas sensor.