Temperature control device for oxygen concentration sensor

摘要

A temperature control device for an oxygen concentration sensor having a solid electrolytic member having oxygen ion-conductivity, a gas diffusion-limiting zone defined by the solid electrolytic member and into which is introduced a gas the concentration of which is to be examined, and a couple of electrodes between which the solid electrolytic member is interposed. Pumping current is supplied to the solid electrolytic member and flows therein between the electrodes to cause an oxygen ion flow in the solid electrolytic member between the electrodes to vary the concentration of oxygen present within the gas diffusion-limiting zone. The pumping current is varied in response to the concentration of oxygen within the gas diffusion-limiting zone, whereby the concentration oxygen in the gas is detected from the pumping current value. The temperature control device comprises a series circuit of an electrically heating element for heating the solid electrolytic member and a switching element, a power supply for supplying a direct current voltage to the series circuit, a current detector for detecting heating current flowing in the heating element, and a driving circuit responsive to the detected heating current for selectively energizing and deenergizing the switching element. A resistance is connected in parallel with the switching element for always allowing the supply of a small amount of current to the heating element irrespective of whether the switching element is energized or deenergized.