Omron SYSMAC C500, Installation Manual

Page: 55 / 112

Section 7
Safety Considerations
50
Introduction
There are certain safety requirements to be considered when installing the
PC. Some of these, such as the emergency stop circuit (refer to
Power Sup-
ply), are part of the initial wiring. The considerations described below should
be kept in mind when operating the PC and when connecting I/O devices to
the PC.
Interlock Circuits
When the PC controls an operation such as the clockwise and counterclock-
wise operation of a motor, provide an external interlock such as the one
shown below to prevent both the forward and reverse outputs from turning
ON at the same time.
PC
MC2
MC1
00501
00502
MC1
MC2
Motor clockwise
Motor counterclockwise
Interlock circuit
This circuit prevents outputs MC1 and MC2 from both being ON at the same
time. Even if the PC is programmed improperly or malfunctions, the motor is
protected.
Power Supply Output
The 24 VDC output of the CPU and Expansion I/O Power Supply may be
used to power other devices. The output current of these supplies is limited
to 0.3 A. A separate Power Supply must be provided if the devices being
powered require a higher current.
Input Leakage Current
When two-wire sensors, such as photoelectric sensors, proximity sensors or
limit switches with LEDs are connected to the PC as input devices, the input
bit may be turned ON erroneously by leakage current. In order to prevent
this, connect a bleeder resistor across the input as shown below.
Sensor
Input
power
supply
Bleeder
resistor
R
PC
If the leakage current is less than 1.3 mA, there should be no problem. If the
leakage current is greater than 1.3 mA, determine the value and rating for the
bleeder resistor using the following formulas.
I = leakage current in mA
7.2
2.4 x I – 3
R = k
Ω
max.
W =
2.3
R
W min.