Echelon FT 3150 Smart Transceiver - Manual (Page 10)

Chapter 1 - Introduction
4 FT 3120/FT 3150 Smart Transceiver Data Book
The FT Smart Transceivers also provide electrical isolation for I/O devices that are grounded, allowing such devices
to be used on a link power network segment. In many applications, some I/O devices are grounded, either to meet
functional requirements or safety regulations. The FT-X1or FT-X2 transformer electrically isolates the device from
the segment, allowing I/O circuitry to be grounded without impairing communications.
A twisted pair channel may be composed of multiple segments separated by EIA 709.1 routers or physical layer
repeaters. A physical layer repeater may be designed using FTT-10A transceivers (the FT Smart Transceivers cannot
be used as physical layer repeaters). The FTT-10A transceiver includes a physical layer repeater feature that allows
L
ON W ORKS data to be exchanged between network segments by interconnecting two or more FTT-10A transceivers.
This allows a twisted pair network to grow inexpensively to encompass many more devices or longer wire distances
than would otherwise be possible. Refer to the L
ON W ORKS FTT-10A Free Topology Transceiver User’s Guide for
more information on this.
The FT Smart Transceivers are designed to comply with both FCC and EN 55022 EMI requirements, minimizing
time-consuming and expensive testing.
Free Topology Technology Overview
A conventional control system using bus topology wiring (such as RS-485) consists of a network of sensors and
actuators that are interconnected using a shielded twisted wire pair. In accordance with RS-485 guidelines, all of the
devices must be wired in a bus topology to limit electrical reflections and ensure reliable communications. There is a
high cost associated with installing and maintaining the cable plant that links together the devices of an RS-485-based
control system. Bus topology wiring is more time consuming and expensive to install, because the installer is unable
to branch or star the wiring where convenient. All devices must be connected directly to the main bus.
The best solution to reduce installation and maintenance costs and to simplify system modifications is to use a free
topology communications system. Echelon's free topology transceiver technology offers such a solution, providing an
elegant and inexpensive method of interconnecting the different elements of a distributed control system.
A free topology architecture allows the installer to wire the control devices with virtually no topology restrictions.
Power is supplied by a local +5VDC power supply located at each device as shown in Figure 1.2.
Figure 1.2 Free Topology Transceiver System
Sensor
Actuator
+5VDC power
Termination
Smart
Device
Transceiver
Smart
Device
Transceiver
To additional
FT 3120 / FT 3150
devices
Smart Transceiver
Smart
Device
Transceiver
Smart
Device
Transceiver
Smart
Device
Transceiver
Smart
Device
Transceiver