Development Of CH₄Gas Alarm Based On Contact Combustion Type Sensor

In recent years, with the rapid development of the national economy, the country’senergy consumption is also rapid growth, but traditional energy sources of coal, oil, lowutilization due to the presence of the high pollution damage to the environment at thesame time, also caused a huge waste of energy, a clean and efficient gas to become theideal alternative energy for several years. As the proportion of national energyconsumption structure and consumption to maintain rapid growth, gas is being used moreand more widely in national product life.These features greatly facilitate the daily lives of people, to meet the needs of theindustrial production, but in actual use, natural gas requires very stringent storage andtransport conditions, otherwise it will leak hidden dangers exist, likely to cause accident,such as a fire or even explosion. This greatly threaten people’s lives. Therefore, todeveloping a gas alarm for home using will be very useful and have practicalsignificance.Through market research, we found that most of the alarm saled on the domesticmarket have some limitations in their design, such as the long stability of gas sensor needimproving, gas alarm software function is too simple to meet the need of home using.These alarm usually use only one level threshold to judge whether the gas concentrationreach the explosion limit. Doing so ignored the danger of low concentrations ofgas,leaving a lot of security risks. For example, if gas leak unevenly distributed, althoughthe overall average concentration does not reach the explosive limit, but may accumulate,the local space explosion is likely to exceed the limit, there is a huge security risk, easilylead to explosions and other safety incidents, threaten to people’s lives and property safetyseriously. In this paper, we design an CH₄alarm based on contact combustion typesensor.In this paper,we designs CH₄alarm controled by microcontroller,and referenceterminal voltage outputed by the signal conditioning circuit, guarantee the conditioningcircuit output voltage between0.5V to2.8V, so that AD converter integrated inmicrocontroller can easily accomplish the analog-to-digital conversion,and then acquisition environment methane concentration data, compared with the pre-set alarmthresholds, if the concentration exceeds the threshold, the microcontroller will performalarm program that is driven sound and light alarm module, a concise way of issuingvoice tone and optical alarm based on logic algorithms. In addition, with the perfect alarmhardware and software design, the alarm system can diagnose some problem and giveinformation to user.In order to upgrade the system,we set an communication interfacewhich can connect to PC. The alarm include the following modules:the methane sensor,the methane sensor driver circuit, methane sensor signal conditioning circuit,analog-to-digital conversion circuit, the system central control unit, alarm function testbutton light and sound alarm unit.In software design of alarm, we design software into different modules to makesystem updata and maintain easily. System software include following parts:alarm systemmalfunction self-diagnostic function module, the methane concentration in real-timeacquisition of functional modules methane concentration data processing function moduleand system alarm logic to determine the functional modules. System fault diagnosisfunction module is a real-time collection and determine whether within the normal rangeoutputed by the methane sensor’s; With the filter of the digital filtering method,microcontroller get the gas concentration from the signal sensor outputed, then systemjudge whether to generate an alarm. The system uses two alarm mode, choose10%LEL（Lower Explosion Limited） as a first alarm threshold and choose20%LEL as secondalarm threshold. In addition, the paper also discusses the alarm electromagneticcompatibility problems in the design stage, proposed to improve the stability andreliability of the alarm.Finally, we complete the principle design of the alarm, the printed circuit board, theprototype welding and debugging of the alarm, and to accomplish the basic functionalityrequired by the design, and make out an prototype gas alarm.