BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
FIG. 1 is a circuit diagram which shows an electric structure of a sensor control circuit of a gas concentration measuring apparatus according to the invention;
FIG. 2 is a transverse sectional view which shows a sensor element used in the gas concentration measuring apparatus as illustrated in FIG. 1;
FIG. 3 shows an example of an applied voltage-to-output current map for use in determining a target voltage to be applied to the sensor element as illustrated in FIG. 2;
FIG. 4 is a graph which shows frequency characteristics of a sensor element, a sensor control circuit, and a combination thereof;
FIG. 5 is a graph which shows changes in gain of output of two types of sensors;
FIG. 6 is a graph which shows increases in gain of frequency characteristics of a sensor control circuit, and a combination of a sensor element and the sensor control circuit;
FIG. 7 is a circuit diagram which shows the first modification of a sensor control circuit of a gas concentration measuring apparatus;
FIG. 8(
a) is a graph which shows increases in gain of frequency characteristics of the sensor control circuit, as illustrated in FIG. 7, and a combination of a sensor element and the sensor control circuit;
FIG. 8(
b) is a graph which shows an increase in level of an output of a sensor current meter of the sensor control circuit representing the current, as produced by the sensor element in FIG. 7;
FIG. 9 is a circuit diagram which shows the second modification of a sensor control circuit of a gas concentration measuring apparatus;
FIG. 10 is a circuit diagram which shows the third modification of a sensor control circuit of a gas concentration measuring apparatus;
FIG. 11(
a) is a graph which shows increases in gain of an output of a sensor current meter of the sensor control circuit, as illustrated in FIG. 10; and
FIG. 11(
b) is a graph which shows an increase in level of an output of the sensor current meter of the sensor control circuit representing the current, as produced by the sensor element in FIG. 10.