Omron SYSMAC C500, Installation Manual

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Section 6
Power Considerations
44
Introduction
Use a commercially available 100 to 120 VAC, 200 to 240 VAC, or 24 VDC
power source, according to the PC you are using (refer to
Appendix B Speci-
fications). Expansion I/O Racks, if used, must also be connected to the
power source. If possible, use independent power sources for the PC, input
devices, and output devices. All Racks of the PC may be connected to one
power source.
Grounding
The Line Ground (LG) terminal is a noise-filtered neutral terminal that does
not normally require grounding. If electrical noise is a problem, however, this
terminal should be connected to the Ground (GR) terminal.
To avoid electrical shock, attach a grounded (earth ground) AWG 14 wire
(cross-sectional area: 2 mm
2
min.) to the GR terminal. The resistance to
ground must be less than 100
Ω
. Do not use a wire longer than 20 m. Care
must be taken, because ground resistance is affected by environmental con-
ditions such as soil composition, water content, time of year, and the length
of time since the wire was laid underground.
PC operation may be adversely affected if the ground wire is shared with
other equipment, or if the ground wire is attached to the metal structure of a
building. When using an Expansion I/O Rack, the Rack must also be
grounded to the GR terminal. The same ground can be used for all connec-
tions.
Power Failure
A sequential circuit is built into the PC to handle power interruptions. This
circuit prevents malfunctions due to momentary power loss or voltage drops.
A timing diagram for the operation of this circuit is shown below.
Momentary power
failure detection time
Approx. 1 s
Power Supply
Power failure
detection signal
CPU voltage (5 V)
Power reset
Run monitor outputs
OFF ON
The PC ignores all momentary power failures if the interruption lasts no
longer than 10 ms. If the interruption lasts between 10 and 25 ms, the inter-
ruption may or may not be detected. If the supply voltage drops below 85%
of the rated voltage for longer that 25 ms (less for the DC Power Supply), the
PC will stop operating and the external outputs will be automatically turned
OFF. Operation is resumed automatically when the voltage is restored to
more than 85% of the rated value.
Wiring
The following diagrams show the proper way to connect the power source to
the PC. The terminals marked “NC” are not connected internally.