Detecting system and detector

Claim 1

A detecting system for detecting a change in an environmental phenomenon comprising: an analog sensor in a detector for sensing said change in a quantity of said environmental phenomenon and having an output signal; said analog sensor having a detection range classified into a plurality of areas correlating with the quantity of said phenomenon; a receiver for receiving and processing a signal corresponding to a detection level of an output from said analog sensor; sensitivity setting means changing automatically a detection sensitivity of said analog sensor when said detection level changes and belongs into another area; said sensitivity setting means comprising: level discriminating means for emitting a discrimination signal indicating which one of areas the output signal from said analog sensor is included in; setting signal emitting means for emitting a sensitivity characteristic level setting signal according to said discrimination signal; correcting means which can hold the output signal level being emitted from said analog sensor so as not to change when the sensitivity characteristics of said analog sensor is changed and so as to prevent the corresponding relationship between the output signal level from the analog sensor and the quantity of the phenomenon from being discontinuous; and drive means for driving a sensing element in said analog sensor to vary according to said setting signal; whereby, said sensitivity of said analog sensor is moved up to a higher level than a current level so as to accomplish a more detailed and precise detection in an area wherein the detection is required, sensitivity of said analog sensor being lowered in the other area wherein a more rough detection than the current level is required.