PURPOSE: To enhance safety and to protect a controlled part of a body, by checking the operating state of a sensor in synchronization with the turning ON of a power source before the start of the working, and reporting the abnormality when it is found in the sensor.
CONSTITUTION: When a key switch 50 is turned ON, a microcomputer 10 executes the program which checks the state of an input port 12a of an input output interface 12. At first, the ON and OFF state of contact points 33 and 34 for up and down commands is checked with respect to a height sensor 39. When the abnormality is detected in the sensor 39, an output port b1 is made to be a high level and a height sensor abnormal lamp 41 is lit. Then the state of outputs terminals 38a, 38b, and 38c of a drum rotational number detecting sensor 38 are checked. When the abnomrality is detected in the sensor 38, an output port b2 is made to be a low level, and a drum rotational number detecting sensor lamp 42 is lit, and thereafter the input from input ports a8Wa10 are nullified.
KOTAKE KAZUO
INADA TETSUYA
