Omron SYSMAC C Series User Manual page 19

Installing the C20
The PC ignores all momentary power failures when the interruption tasts
no longer than 10msec. If the interruption is more than 10msec, but less
than 20msec, it may or may not be detected. Failures longer than 20msec
will cause the PC to stop operating; external output relays are
automatically turned off.
Operation automatically resumes when the supply voltage is restored to
more than 85% of the rated voltage.
When the expansion I/O unit (3G2C7-MC ) is used, an external
power supply is required to drive the relays. This external power supply is
not necessary when only the CPU is used.
External power supply|
(for relay driving)
SYSMAC-C20 Expansion I/O unit
(8G2C7-MCOO0)
When a two-wire sensor is used for the input, the input signal may be
turned ON by a leakage current exceeding 3mA. To prevent this, connect
a bleeder resistor of 7.5kO or less as shown.
Power source
C20 input circuit
Two-wire
sensor