DETECTION SYSTEM FOR ABNORMALITY OF INFRARED DETECTION PART IN THERMOGRAPHY DEVICE

摘要

PURPOSE:To accurately detect the shortage of liquid nitrogen by switching an optical system chopper when no infrared ray is detected from a subject and monitoring an inserted reference signal. CONSTITUTION:A scanning mirror 2 makes an optical surface scan on the subject 1 and the infrared ray from the surface-scanned subject 1 is converged by a concave mirror 3 and detected by a detecting element 8 through a reflecting mirror 6 and a lens 7. The chopper 4 chops the infrared ray from the subject 1 in synchronism with the vibration period of the scanning mirror 2 and also inserts the reference signal when no infrared ray is detected from the subject 1. Then, even when the infrared ray is too low to reach the detection level of the detecting element 8, the reference signal is obtained as the detection output of the detecting element 8 at every scanning period. If, however, liquid nitrogen for cooling the detecting element 8 becomes less until a normal detection state is not obtained, either the infrared ray from the detecting element 8 nor the detection signal of the reference signal is obtained. For the purpose, this reference signal is monitored all the time to decide the operation state of the detecting element.