Omron 3G8F7-CRM21, User Manual

Page: 228 / 238

208
Wiring for Power Supply
Section E-5
E-5-6 Precautions when Providing the I/O Power Supply
When building a system, consideration must be given to the methods to
supply the communications and the I/O power. The consideration includes not
only the hardware elements, such as selecting power supplies and cables that
confirm the allowable currents and the voltage drop, but also cost and
software factors, such as system operation at power supply errors.
Supplying I/O Power from One Source
In a system where the I/O power is supplied collectively from one source,
the power consumption by individual device and load must also be
considered. Cable selection must satisfy that the power supplied to the last
Slave Unit or load is within the allowable voltage range.
Furthermore, attention should be paid to the power supply capacity and that
the total line current is within the allowable current range of the cable.
The following measures can be considered to keep the voltage drop within the
allowable range in a network with a single power supply.
• Increase the thickness of the cables.
• Increase the output voltage of the power supply.
• Shorten the wiring.
• Locate the power supply in the middle of the network.
Supplying I/O Power from Multiple Sources
Supplying the I/O power from multiple sources, instead of a single source, is
effective to reduce the line current, the voltage drop, and the cable size. This
method should be considered to ensure system safety at power errors.
Slave Unit Slave Unit Slave Unit Slave Unit
Load Load Load Load
Design the wiring so that
stable power voltage is
supplied to the end load.
If a stable power voltage cannot be supplied to the end load,
place the power supply in the middle of the network.
I
4
I
3
I
2
I
1
∆
E
4
∆
E
∆
E
∆
E
3 2 1
24-VDC Power
Supply
24-VDC Power
Supply
Slave
Power supply
(24 VDC)
Slave Slave Slave
Power supply
(24 VDC)