Pathway DMX Pathfinder CR Manual - Manual (Page 10)

DMX Distribution System Page 10
Operation
(daisy-chain) topology to avoid the troublesome effects of signal reflection
caused by a star wiring configuration.
.11 Line Loading -- The star wiring configuration described above would also be
prone to excessive loading of the data line with too many DMX receivers.
Recall that an RS485 line driver is capable (under ideal conditions) of
supporting up to 32 receivers.
.12 Line Length -- Data signals do not travel over long distances without being
subjected to distortion and losses (or attenuation). Distortion effects are
compounded by moderate to excessive line loading.
.13 Repeaters -- The best solution to the three problems described above is to
use a signal repeater at the start of each run of data cable from the
distribution rack to the receiver station. Also known as a regenerative
repeater, this circuit receives a DMX signal from a data source and re-
creates it free of any losses or distortion effects. Repeaters differ from
amplifiers in that amplifiers increase the energy of the source signal (as well
as the amount of distortion present in the signal). Another advantage of
using a repeater is that the source signal can be routed to several parallel
repeater circuits at once, multiplying the "fan-out" of the transmitted signals
virtually infinitely.
.14 Opto-Isolation -- Opto-isolation involves the insertion of an electrical
separation or isolation stage into the data communications channel. This is
typically done for two reasons: a) to eliminate current loops due to ground
voltage potential between data source and receiver data cable shielding; and
b) to prevent high voltages caused by faulty equipment or cabling from
propagating throughout the rest of the data communications system and
causing severe damage. The conventional method of separation involves
the use of opto-isolators, which are self-contained integrated circuits
providing up to 2500 volts of isolation.
Repeaters and opto-isolators are combined into the same modules in the DMX
Distribution System, called opto-repeaters or opto-splitters, each of which routes
one to four source signals to four separate output signal channels. As previously