Dmx Basics; Signal Transmission; The Cabling - GLP SCAN OPERATOR FX User Manual

2 DMX Basics

To operate the Scanoperator FX, a basic knowledge about the DMX signal
transmission, is necessary. This chapter offers a short introduction to the world of DMX
data transmission and addresses to beginners and those who have no, or just a little
experience with DMX.
2.1

Signal transmission

Up to 512 DMX channels can be transferred over a so called DMX cable during a DMX
signal transmission. Every DMX channel equals a value of numbers between 0 and 255.
A lightcontroller generates the DMX channels and constantly continues them with
current values. The Scanoperator FX sends 192 channels with a rate of repeatition of
36Hz. That means, that every one of the192 channels is sent 36 times per second.

The cabling

2.2
DMX fixtures are being cabled in series. There is only one transmitter but several
receivers. The order of receivers on a cable does not matter, because all units receive
all data and filter the relevant data. The cabling starts at the transmitter (the lightdesk)
and leads to the first DMX set. Beginning at the first DMX Fixture, there's a cable
leading to the second and so on, until the last set is reached. According to the standard
you need to plug in a DMX terminator into the last fixture. You can do without this plug if
you have smaller cable lengths (20m-30m length of the cable). But please keep in mind,
that without that plug, errors might show up in the DMX cabling. The maximum length of
the cable is 300m. You can overcome longer distances by a DMX Signal Booster.
Reference:
A DMX Terminator plug is the same as an ordinary XLR plug, where both DMX data
pins (data+ and data-) are connected over a 120Ohm resistor. This minimizes the
reflections at the end of the cable, which clearly raises the signal quality.
The DMX cables normally consist of one cable according to AES/EBU standard with 5
pin XLR plugs. Instead of using AES/EBU standard cables, often normal microphone
cable is being used. This should be considered like not using a Terminator plug: in case
of shorter distances it usually works – but might show errors in the DMX cabling as well.
GLP • German Light Products
(V1.3)
SCAN OPERATOR FX
11