64
7-1 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 ever both being ON at the same
time. Even if the PC is programmed improperly or malfunctions, the motor is pro-
tected.
7-2 Power Supply Output
Power Supply Output The 12 or 24 VDC output of the CPU Unit 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.
7-3 Input Circuits
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, con-
nect 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 leak-
age current is greater than 1.3 mA, determine the resistance and power rating
for the bleeder resistor using the following formulas.
For standard I/O Units:
7.2
2.4 x I – 3
––––––
R =
kΩ max.
W =
2.3
R
–––
W min.
I = leakage current in mA
Input Circuits Section 7-3
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