| 摘要 |
PURPOSE: To detect whether a flame is generated or not at high precision by comparing the output change of an infrared detector at the time of starting operation of a chopper with a back ground level obtained by measurement. CONSTITUTION: When the periodical driving of a liquid crystal chopper 3 is started, and when the quantity of radiated light to an infrared detector 1 is altered and an output signal V is oscillated, V>±VO (VO: threshold value) is satisfied and the output signal V passes a waveform shaping circuit 6 and is stored as data related to back ground level in a memory 9. In the case of V>±VO due to the flucturation of flame generated actually, the amplitude of an output signal V, that is VDC level of the converting-into-d.c. circuit 8, becomes higher than the back ground level by the equivalent quantity of the radiated light from CO2 in the flames and the output of a comparator 10 becomes H level. Meanwhile, in the case of V>±VO due to external disturbance, the output has the value with no difference from the back ground level, so that the output signal of the comparator 10 becomes L level.
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