| 摘要 |
<P>PROBLEM TO BE SOLVED: To extract an electric signal from a photodiode even in case of a power failure and not to terminate the photodiode with a resistance in normal operation. <P>SOLUTION: A series circuit of a Zener diode ZD, a resistance R1, a coil L and a photodiode PD is connected between a power source +Vcc and a ground, and a bias is applied to the photodiode PD through the Zener diode ZD and resistance R1. An electric signal extracted from one end of the photodiode PD is input to a movable contact (a) of a relay RY. When the power source +Vcc is supplied, the relay RY is switched to the side of a normally closed contact (b), and the electric signal is input to a first amplification unit 10. Further, the relay RY is switched to the side of a normally open contact (c) in case of a power failure, and the photodiode PD is terminated with the resistance R2, so that an electric signal extracted from both ends of the resistance R2 is output from a monitor terminal J2 through a branch circuit 14. <P>COPYRIGHT: (C)2010,JPO&INPIT |
