LSC Lighting Redback Operators Manual - Manual (Page 21)

Redback Dimmer DMX512 Explained
Operator Manual V1.1
LSC Lighting Systems (Aust) Pty. Ltd Page 19
7 D M X 5 1 2 E x p l a i n e d
DMX512-A is the industry standard for the transmission of digital control signals between lighting
equipment. It utilises just a single pair of wires on which is transmitted the level information for the control
of up to 512 DMX slots (addresses or channels).
The information for each slot is sent sequentially. The level of slot 1 is transmitted, then the level of slot 2,
then 3, etc. up to a maximum of 512 slots. This stream of data containing the levels for all 512 DMX slots
is repeated a minimum (generally) of 44 times per second. This provides sufficient updates of channel
information for smooth fade transitions.
As the DMX512-A signal contains the level information for all slots, each piece of equipment needs to be
able to read the level(s) of the slots(s) that apply only to that piece of equipment. To enable this, the
Redback dimmer has a “SPatch” (softpatch) menu that allows you to patch (connect) each DMX slot
(address) from your lighting controller to a Redback dimmer channel number.
When good quality data cables are used, DMX512 cable runs may be up to 1,000 metres in length. When
several DMX feeds are required (to feed different locations), DMX512 splitters must be used. These
provides multiple isolated DMX512 feeds.
The Redback uses a high impedance DMX input circuit allowing you to loop the DMX signal from one
Redback to the next. The last Redback in the chain will require a DMX Termination device plugged in to
the Thru socket.
Note: Do not use unscreened microphone or low speed data cables for DMX. This can cause problems in
the DMX network. Make sure the cable conforms to the EIA485 cable requirements by providing the
following specifications:
• Low
capacitance
• One or more twisted pairs
• Foil and braid shielded
• Impedance of 85 -150 Ohms, nominally 120 Ohms
• 22AWG gauge for continuous lengths over 300 metres
7.1 Typical DMX Installations
In the following example, the DMX output signal from the lighting control desk is fed to the DMX
connector of the first Redback dimmer. The DMX cable is then looped to the following Redback
dimmers. The order of the daisy chaining is not important as each Redback dimmer channel can be
patched to any DMX slot number. The end of the DMX line is terminated to prevent the signal reflecting
back up the line and causing possible errors.
Redback
12
DMX
Slots
13-24
Redback
12
DMX
Slots
31 42
Redback
6
DMX
Slots
7-12
Redback
6
DMX
Slots
1-6
Lighting
Controller
Terminating
device in
DMX THRU
socket on
Redback
DMX
Cable