| 摘要 |
<p>PURPOSE:To get rid of an acoustic signal caused by a noise signal, by comparing with a reference voltage a DC voltage due to a dark current depending on a cooling temperature of a cooled type photo detector, by switching the input to an acoustic amplifier to input an alarm signal to the acoustic amplifier. CONSTITUTION:When a cooled type photo detector 1 is cooled, a dark current flows according to a difference between an ambient temperature and the temperature of the detector. Accordingly a DC voltage is generated at an output terminal of a preamplifier 2. Under such a condition, when an infrared-ray energy is chopped from a target object, the dark current is overlapped with an alternating current corresponding to the intensity of the energy to be converted to a voltage. An output of the amplifier 2 is cut by a DC portion attributed to the dark current with a capacitor 3 and amplified with a band filter amplifier 4 by an AC portion corresponding to an infrared incident energy to make an input signal to an error signal processing circuit 5 and an acoustic amplifier 6. An output of the amplifier 2 is also supplied to a smoothing circuit 7, where only a DC portion thereof is turned to an input signal to a comparator 8. The current input signal is compared with an output of a reference voltage generator 11 and when it is below the reference voltage, the comparator 8 outputs a drive signal of a relay 9.</p> |
