| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal input circuit which can suppress heat generation even when connected to external equipment performing on/off operation other than a two- wire type sensor while suppressing a rise in const and an increase in the size of a device. SOLUTION: When the two-wire type sensor 3 is connected, the output terminal and ground terminal of the two-wire type sensor 3 are connected to the input terminal Si3 and ground terminal Si2 of the input circuit 10. An input resistance R1 has its resistance value set corresponding to the current value of a standby current of the two-wire type sensor 3, so even when the two-wire type sensor 3 is off, electric power which is large enough to drive the two-wire type sensor 3 is supplied. When a three- wire sensor 4 is connected, on the other hand, the power terminals of the three-wire type sensor 4 are connected to the power terminals (So1, So2) of the input circuit 10 and the output terminal of the three-wire type sensor 4 is connected to the input terminal Si4 of the input circuit 10. An input resistance R2 has its resistance value set larger than the input resistance R1, so even when the three-wire type sensor 4 is on, the amount of the current flowing to the input resistance R1 is suppressed to reduce the heat generation as compared with the use of the input resistance R2 having the small resistance value.
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