| 摘要 |
<p>PURPOSE: To prevent an erroneous report from being caused due to the slow change of pneumatic pressure within a monitoring area by comparing the signal detected in a moment with a variable delay reference signal. CONSTITUTION: A sensor 11 such as a microphone, etc., sensing the change of pneumatic pressure is arranged within a block area to be monitored such as the compartment of an automobile, the output of the sensor 11 is amplified by an amplifier 13, the output passes a low pass filter passing only the super low frequency signal composed of C3, C4 and C5, and the super low frequency signals are extracted. The extracted super low frequency signals pass each of two parted signal paths and the signals are supplied to both inputs of a comparator 14. The one signal path has time delay circuits R6 and C5, and the super low frequency signal passing this signal path functions as a variable reference. Because a detector performs a self-adjustment in this way, an alarm signal is generated from the comparator based on only rapidly changed super low frequency signals. Thus, the sensitivity of the detector is improved and an erroneous report is prevented.</p> |
