User`s guide

LONWORKS LPT-10 Transceiver User’s Guide 1-3
Applications
A conventional control system using bus topology wiring (such as RS-485) consists of a
network of sensors and control outputs that are interconnected using a shielded twisted
wire pair. In accordance with EIA 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 many elements 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 installation of local power supplies for each device is especially
expensive since it usually involves an AC mains connection.
Installing separate data and power wiring also implies that a technician's time will be
spent troubleshooting the wiring harness to isolate and repair cable faults. Moreover,
each time a sensor is added or an actuator is moved, both data and power wiring must be
changed accordingly, often resulting in network down time until the new connections can
be established.
The best solution for reducing installation and maintenance costs and simplifying
system modifications is a free topology communication system that combines power and
data on a common twisted wire pair. Echelon's link power technology offers just such a
solution, and provides an elegant and inexpensive method of interconnecting the
different elements of a distributed control system.
The link power system sends power and data on a common twisted wire pair, and allows
the user to wire the control devices with virtually no topology restrictions. Power is
supplied by a customer-furnished nominal 48VDC power supply, and flows through an
LPI-10 Power Supply Interface onto the twisted pair wire (figure 1.1). The LPI-10
module isolates the power supply from wiring faults on the twisted pair, couples power
to the system wiring, and terminates the twisted pair network.
There are two version of the LPI-10 interface: a simple, low-cost, inductor-based design
intended for customers who are building power supplies, and an electronic LPI-10
interface designed for use with off-the-shelf 48VDC power supplies.