operating range installations utilizing gases having low heat content such as landfill and wood gas may have exhaust temperatures below the minimum operating temperature of the zirconium oxide cell 100 in these instances the zirconium oxide cell 100 may be placed in a temperature controlled oven not illustrated within which the temperature is maintained at for example 1500 u00b0 fahrenheit and exposed as described to the exhaust gases disposed in this fashion there is no need for temperature compensation of the output of the zirconium oxide cell 100 provided by the compensation amplifier 106 the analog divider 116 provides a temperature compensated ramp signal which represents the percent of oxygen in the exhaust gases within the manifold 14 the output of the analog divider 116 is fed to a first pair of comparators 120 and 122 and a second pair of comparators 124 and 126 each of the comparators 122 124 126 and 128 includes an associated threshold control 130 132 134 and 136 respectively the threshold controls 130 132 134 and 136 permit adjustment of the switch point of the comparators 122 through 128 and provide variable hysteresis operation of the system 10 in a manner to be described subsequently the outputs of the first pair of comparators 120 and 122 drives a flip flop memory.