Doug Fleenor Design DMXOPTO-5 - Manual (Page 6)

5
Isolating the middle dimmers from reflections may be accomplished
by placing a DMX Optical Isolator at the "loop through"
connection of the dimmer in the middle of the control line.
Since the isolator is a "one-way" device (receiving a signal on
it's input and re-transmitting it on it's output) the reflection
cannot go backwards through the isolator and distort the signal
reaching the middle dimmer:
+---------+ +--------+ +----------+ +--------+
| CONSOLE |----------| DIMMER |-| ISOLATOR |-----------| DIMMER |
+---------+ +--------+ +----------+ +--------+
The DMX Optical Isolator has a passive input which loads the
control line more than a dimmer. If there are lots of dimmers
ahead of the isolator, the console may not be able to drive all
the dimmers and the isolator too. Although not likely, if
placing the isolator after the dimmers causes the dimmers to
flicker or blink, try placing the isolator just ahead of the
middle dimmers:
+---------+ +----------+ +---------+ +--------+
| CONSOLE |---------| ISOLATOR |-| DIMMERS |-----------| DIMMER |
+---------+ +----------+ +---------+ +--------+
This configuration does not "isolate" the reflections but
"suppresses" them by supplying a very strong, re-transmitted
signal to the middle dimmers.
It's not just because we make the isolator that we present the
next solution (but we don't mind selling all those isolators
either):
+-------+ +--------+ +--------+ +---+ +--------+ +---+
|CONSOLE|-|ISOLATOR|------|ISOLATOR|-|DIM|-|ISOLATOR|------|DIM|
+-------+ +--------+ +--------+ +---+ +--------+ +---+
In some cases this may be overkill... but it can't hurt. In fact
the need to daisy chain isolators is the main reason the DMX
Optical Isolator is 40 times faster than the DMX512 data rate; so
that daisy chaining will not degrade the signal quality. And
just look at all the protection you get from dimmer failure and
storm damage!