| 摘要 |
PROBLEM TO BE SOLVED: To automatically calibrate a concentration reference value without depending on a measuring atmosphere and to detect a concentration over a wide range by a method wherein a second impedance measuring means by which the impedance of a carbon dioxide gas sensor is measured at a frequency for calibration is installed and the concentration reference value is computed at a prescribed timing so as to be updated. SOLUTION: First, when a calibration-timing judgment means 303 judges the passage of, e.g. 30 minutes, an impedance measuring means 306 measures the impedance of a carbon dioxide gas sensor 302 at 1 MHz. Then, a reference-value storage means 307 computes a reference value up to 100 kHz on the basis of a measured value so as to be stored. Then, an impedance measuring means 304 measures a sensor output value at 100 kHz so as to be stored on a sensor-output-value storage means 305. Then, on the basis of the reference value which is stored on the means 307 and on the basis of the sensor output value which is stored on the means 305, a concentration computing means 308 computes the concentration of carbon dioxide in a measuring atmosphere so as to be output. After that, the elapse state of a prescribed time is judged by the means 303. When the time has elapsed, it is calibrated, and the reference value is updated. When the time has not elapsed, the reference value is not calibrated so as to continue a measurement. |
