PURPOSE: To prevent gases and water from adhering to an ambient air sensor and precisely detect the ambient air in the environment by heating the ambient air sensor at low temperature by applying small electric current at normal time. ;CONSTITUTION: Small current is applied to an atmospheric sensor to carry out heat radiation at as low temperature as about 100°C, so that adhesion of gases and water to the atmospheric sensor which sometimes causes a detection error can be prevented. Detection of ambient temperature is carried out during the low temperature heating period and detection of the atmosphere is carried out during the time when the atmospheric sensor is heated to high temperature. In this ways, heating to high temperature can be done only by increasing the intensity of the current to be applied to the atmospheric sensor. In the case, for example, 2mA current is for the time of low temperature heating and 8mA current for the time of high temperature heating, a rated current power source with 6mA should be prepared and detection can be carried out only by turning the rated current power source on or off. Consequently, not like a conventional one, a switching circuit is made no need and a pause period in which gases and water adheres to the atmospheric sensor can be shortened. As a result, the atmosphere in the environment can be detected precisely.;COPYRIGHT: (C)1996,JPO
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