Patent ID: 7968837

Claim:
A separated smoke sensor comprising: a light transmitting unit configured to wirelessly transmit detection light to a monitoring area; and a light receiving unit configured to wirelessly receive detection light transmitted by the light transmitting unit to the monitoring area, determine presence of smoke in the monitoring area based on a detection amount of the received detection light, and output an accident-warning signal to a receiving device that is connected to the light receiving unit via a line when the light receiving unit determines that smoke is present; wherein the light transmitting unit and the light receiving unit are laid out separately from each other and facing each other, sandwiching the monitoring area; wherein the light transmitting unit is configured to receive electric power from a local power source connected to the light transmitting unit or from a battery incorporated within the light transmitting unit; wherein the light receiving unit is configured to receive electric power from the receiving device: wherein the light transmitting unit having a light source and a light-transmission control unit; wherein the light source is configured to wirelessly transmit the detection light; wherein the light-transmission control unit is configured to control transmission of the detection light by the light source by a predetermined transmission time at a predetermined light transmission interval; wherein the light receiving unit includes: a light receiving element configured to wirelessly receive the detection light transmitted by the light source and output a voltage or a current corresponding to an amount of the received detection light; a synchronization-establishment processing unit configured to: execute a predetermined process establishing synchronization between the light transmitting unit and the light receiving unit based on the detection light received by the light receiving element; execute a predetermined light reception operation that receives the detection light by a predetermined reception time at a predetermined light reception interval different from the light transmission interval; determine presence of reception of the detection light during the light reception operation, and when reception is determined; and specify, as a synchronization timing, a timing that arrives at a same interval as the predetermined light transmission interval, based on a timing at which the detection light is received; a light-extinction-amount calculation unit configured to calculate a light extinction amount of the detection light received by the light receiving element based on a voltage or current output by the light receiving element at the synchronization timing established by the synchronization-establishment processing unit; and a smoke determining unit that determines the presence of smoke in the monitoring area based on the light extinction amount calculated by the light-extinction-amount calculation unit and a predetermined threshold value.