| 摘要 |
PURPOSE:To eliminate a secular change in the infrared detection sensitivity of a detector from affecting inspection and decision making even in case the secular change by comparing the detection signal of an infrared detector with a predetermined reference level and calibrating the gain of an amplifier according to the comparison result. CONSTITUTION:The detection signal of the infrared detector 1 composed of an infrared detecting element 2 and a lens 3 is amplified by am amplifier 4 whose gain is varied with an external signal and then the amplified signal is processed by a signal processor 5 to perform defect detection. A divider 6, on the other hand, receives the detection signal of the detector 1 and the preset reference level e0 is divided by its detection signal er. Then, the rate e0/er of the calibration of the initial gain G0 of the amplifier G0 based upon the division result is sent to a sensitivity setter 7. The gain Gr after the calibration which is obtained through the arithmetic operation of the setter 7 based upon a specific expression is sent to the amplifier 4, whose gain is calibrated. Thus, the gain of the amplifier 4 is controlled to obtain the same signal as that in case the infrared detection sensitivity is constant by the signal processor 5 even if the infrared detection sensitivity varies.
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