| 摘要 |
PURPOSE:To permit accurate detection irrespective of the presence or absence of miscellaneous gas and to eliminate erroneous alarm by a circuit wherein output resistance of a detecting element is switched in accordance with output of a reference element having sensitivity for only the miscellaneous gas, and an alarm level is set correspondingly thereto. CONSTITUTION:A detecting element 6 has sensitivity for both the detected gas and miscellaneous gas, while a reference element 8 has sensitivity not for the detected gas substantially but for the miscellaneous gas only. The miscellaneous gas is measured by the element 8 and the measured resistance change is applied to an alarm level setting circuit 10, which issues output in accordance with its input voltage to a voltage comparison circuit 11. The circuit 11 compares the output of the circuit 10 with the output of the element 6 and then issues an alarm. At this time, the reading resistance value of the element 6 is automatically switched in sequence based on the output corresponding to the miscellaneous gas detected by the element 8 and, simultaneously, the alarm level setting circuit is used to enlarge a change in output of the element 6 with respect to increase or reduction of the detected gas. |
