PURPOSE: To improve the performance of a device by automatically inspecting the failure of a working alarm device for securing the safety of workers or the like by utilizing ultrasonic waves and further providing a means capable of easily changing directivity and discriminating the existing direction of an object.
CONSTITUTION: This method is provided with plural ultrasonic nodes 21-24, an RS422 cable 25, an RS422 transceiver 20, a CPU 1, a RAM 3, an input means 18, an alarm output means 4 and a display means 19. With this constitution, a desired area can be set to a dangerous condition detection area, the existing direction of a dangerous object can be discriminated as well and the working alarm device for self-checking the failure of the ultrasonic nodes 21-24 can be provided.
KAMIYA YOSHINORI
TAKIGUCHI ISAO
