Emerson Rosemount 1410S Reference Manual page 30

Installing the Gateway
December 2023
Switch 2 is connected to a 120 Ω terminating resistor for Modbus connection. This resistor
is used to dampen signal reflections on long cable runs. RS-485 specifications indicate the
data bus should be terminated at both ends
3.5.7 Power over Ethernet (PoE)
This Gateway is equipped with PoE technology to derive its power from another PoE device
via the Ethernet connection (PD mode). This device complies with the IEEE 802.3af-2003 or
IEEE 802.3at -2009 for PD operation.
These standards require the use of Category 5 Ethernet cable or higher. In the operation
of IEEE 802.3a, PoE power is only transmitted from one device to another when the proper
impedance match is made. This prevents damage to non PoE devices on the network.
To use this feature, the Gateway must be connected over the Ethernet to a matching IEEE
802.3a device. Failure to do this will cause no power sourced. A switch on the power supply
board allows a PD (Powered Device) to be enabled or disabled.
PoE advantages
To save costs on planning, wiring and installation of networks, devices are supplied with
power directly via the Ethernet cable (e.g. via a Cat 5/5e cable up to 100 m). PoE makes
the network planning flexible, independent of power supply cabinets, and junction boxes.
There are no extra costs for the electrical wiring. An advantage of PoE is that you can install
devices with an Ethernet interface in places of difficult access or in areas in which running
cable would be inconvenient. This in turn saves installation time and costs. This technology
is in use today typically in IP telephones, cameras, or wireless transmission devices such as
WLAN Access Points.
An excellent application is a Gateway connected to a Wi-Fi back haul unit; such as a Cisco
unit. For example, a Cisco IW6300 unit could power the Gateway over a PoE connection.
Selecting devices to work with a PoE Gateway
When connecting the Gateway to a PSE device, the device must be labeled as compliant
with IEEE 802.3af or IEEE 802.3at. Many companies use labels on their packaging such
as PoE for IEEE 802.3af or PoE+ for IEEE 802.3at. Check the specific manufacturer's
specifications of any device to make sure IEEE 802.3 is referenced; otherwise the
connection may not work.
Caution is needed in selecting a companion device to the Gateway for PoE. Not all devices
labeled PoE will function. Before 2003, there was no standard and companies developed
their own techniques for powering over an Ethernet cable. These techniques are not
always interoperable. Before the standard, they used the term PoE on many of their
products. Most new products labeled PoE are IEEE compatible. Cisco products can be
ordered with their old standard (Online Power as it is sometimes referred to) or with the
IEEE 802.3 PoE standard. If in doubt, check with the appropriate manufacturer before
purchasing/installing the connecting equipment.
For reference, Cisco offers the following four versions:
1. Pre standard PoE (Online Power)
2. 802.3af-compliant PoE (15W)
3. 802.3at-compliant PoE Plus (PoE+) (25W)
4. Universal PoE (UPoE) (60W). (New Cisco standard, which Cisco claims is compatible
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with IEEE 802.3af PoE and IEEE 802.3at PoE +)
(Figure 3-8).
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