Ricoh Company, Ltd.

Ricoh Seiki Company, Ltd.

Minoru Miyoshi

Junji Manaka

Toshiaki Mizuta

A gas sensor includes a pair of lead strips, a sensing element preferably comprised of a metal oxide semiconductor, such as SnO.sub.2, and extending between the pair of lead strips in the form of a bridge, a heater driver for supplying a heating current to at least one of the pair of lead strips, a detector for detecting a predetermined property of the sensing element, and a control circuit for controlling the operation of the heater driver and the detector. In one form of the invention, the detector is activated in a time period in which the heater driver is not activated. In another form of the invention, the pair of lead strips are connected in parallel or in series when the heater driver is to be activated. In a further form of the invention, the heater driver is normally operated periodically, but when the detector first detects a predetermined condition, the heater driver is operated continuously.

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Yokohama, Japan

Minoru Miyoshi