To provide a sensor dealing with a differentiated value which can inform fact to a user through alarm, when an absolute value of characteristic amount which originates from contamination of a sensor head, temperature drift, element deterioration, etc. and is obtained from a detection object reduces gradually, so that the absolute value deviates from tolerance necessary for differentiated value decision.
When variation is generated in the characteristic amount obtained from a detection object region, and the amount of variation exceeds a threshold value, the so-called sensor dealing with a differentiated value generates a decision output of presence or absence of an object in the detection object region. In the sensor, an alarm means is installed which decides that the value of obtained characteristic amount deviates from the tolerance necessary for decision of presence or absence of object, and performs alarm operation of the fact.
GONDO KIYOHIKO
KAMEI TAKASHI
