JPS57163862A - Detecting circuit of oxygen concentration sensor - Google Patents

Abstract

PURPOSE:To decide the activation an O2 sensor, by accuratly measuring the internal resistance of the O2 sensor regardless of fluctuations of electromotive force of the O2 sensor. CONSTITUTION:An O2 sensor 11 consists of a series circuit of an internal resistance 12 and a sensor electromotive force 13. Output voltage of the sensor 11 is sample held by a sample holding circuit 19 through a buffer circuit 18 and a degree of O2 concentration is detected by comparing said sample holding voltage with a standard voltage 22 by a level comparator 21 and its signal is outputted into a terminal 23. When a switching element 19 is switched ON by a clock signal inputted from the terminal 31, a series circuit is constituted by a load resistance 17, an internal resistance 12 and a sensor electromotive force 13. Voltage of each of connecting points 27 and 26 of a standard block 35 having the same constitution as a block 34 entirely is inputted into a level comparator 28 and the voltage of the point 27 is measured by comparing with the voltage of the point 26 taken as a standard, and the capacity of the internal resistance 12, that is, a signal either the sensor is in an activated state or not, is outputted into a terminal 30.