Installation guide

Installation
890USE17100 September 2003 31
Determining
Power
Distribution
Requirements
The island bus is designed to distribute field power to all its I/O modules over
separate sensor buses (to the input modules) and actuator buses (to the output
modules). The modules used to distribute field power are called PDMs. Two PDM
modules are available:
The STB PDT 3100, which distributes 24 VDC field power
The STB PDT 2100, which can distribute either 115 VAC field power or 230 VAC
field power
In general, analog I/O and relay output modules rely on STB PDT 3100 24 VDC
PDMs for power distribution. Some digital modules (with DDI or DDO in the model
number) rely on STB PDT 3100 PDMs, while other digital modules (with DAI and
DAO model numbers) rely on STB PDT 2100 VAC PDMs for power distribution.
The PDM needs to be installed directly to the left of the I/O modules to which it is
distributing field power. If you intend to support both VDC I/O modules and VAC I/O
modules in the same segment, you will need to install different PDMs in the segment
to support the different voltage groups.
As you plan your island layout, it is important to remember that all the I/O modules
that require 24 VDC need to be placed together in a voltage group that is separated
from any 115 or 230 VAC modules. Likewise, all I/O modules that require 115 VAC
need to be separated from any 230 VDC modules in the segment.
The following illustration shows a primary segment with two voltage groups in it. The
PDMs are used both to distribute power to their I/O modules and to segregate their
I/O modules from other voltage groups.
Note: For better immunity in noisy environments It is recommended, but not
imperative, that in the event a segment consists of groups of AC and DC I/O
modules, the AC group be placed before the DC group (from left to right).