Configuration Manual Owner manual

Publication 1757-PM002A-EN-E - June 2006
Set Up A System 2-7
Physical Media
Power Considerations
Fieldbus devices may be either powered from the segment (bus) or locally
powered, depending on the design. If at all possible, field devices should be
bus powered.
Power Supplies
Power supplies shall comply with IEC 61158-2 criteria and performance
requirements, with preferential consideration given to the low-power signal
option. We recommend using one power supply dedicated to the linking device
and any additional supplies dedicated toward the field devices.
Rockwell Automation manufactures a DIN rail mountable 1794-PS3 supply
that is Class 1, DIV2 compliant. It will supply +24VDC at 3 Amps.
Power Conditioning
If an ordinary power supply were used to power the fieldbus, the power supply
would absorb signals on the cable because it would try and maintain a constant
voltage level. For this reason, an ordinary power supply must be conditioned
for fieldbus use.
Putting an inductor between the power supply and the fieldbus wiring is a way
to isolate the fieldbus signal from the low impedance of the bulk supply. The
inductor lets in the DC power on the wiring, but it prevents signals from going
into the power supply.
One fieldbus power supply conditioner is required for each fieldbus network
segment (
Figure 2.2).
Figure 2.2 Power Supply With One Power Conditioner
Power conditioners should be redundant units that provide flawless transfer
from one unit to another. Primary and secondary sources should be
physically separated, not sharing a common backplane or AC source. Be
aware that power conditioners have limits on how much current they can
source.
DC Power Supply
Conditioner H1 Fieldbus