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WHAT IS DMX?
DMX stands for "Digital-Multiplexing".
The DMX system is a high-speed digital data
system, which can transmit all the information required for light dimmers,
multi-motor lighting effects etc. down a single cable, like a computer talking
to a printer. Up to 32 DMX controlled
products may be connected to the DMX signal on a single cable, and it is
recommended that the total cable length should not exceed 250m. Some controllers
have more than one output enabling the connection of 32 DMX controlled products
per output (See Merlin)
Each product connected to the DMX signal is given an "Address" (By
setting switches or a digital display), and it compares this to the data being
sent on the DMX cable, so it can determine which data is addressed to it. It
then uses this data to move a motor or set a brightness level as required by the
controller. As the DMX system can transmit as much information as 512 analogue
control wires down a single cable, it has to transmit very quickly, in fact, at
a frequency 12 times higher than the highest audio frequency.
Anyone who has used long leads for audio will realize that it is difficult to do
without losing the higher frequencies. To make the DMX system work at such high
frequencies, it requires special circuitry and special cable. Cable can be
designed to pass high frequencies with no loss if it has the correct resistance
connected at each end. Without it, the signal reflects off the end of the cable
and interferes with the new data coming the other way. If the cable is not
correct, the system will not work. Most good quality low-capacitance screened
twisted pair cables will work (Balanced Line microphone cable), but
twin individually screened
will not work. Also, if the cable is split or joined other
than end-to-end, the system will stop working.
It is recommended that a Termination resistor
(120W) is
connected across the positive and negative pins on the "out" socket of the last
product in a DMX chain to prevent data being corrupted by a reflected signal
boucing back off the open end of the chain.
More information can be gained by attending a
"MERLIN SEMINAR"
Merlin Seminars are held on the first
Wednesday in the month at the Premier Solutions premises.
(See Map)
The seminar lasts from approximately 10.00am to 3.00pm and is open to all.
The seminar covers an explanation of DMX
and
0-10V lighting control
as well as all aspects of the features and
programming of the Merlin Lighting Desk,
including "hands on" tuition on the
desk itself.
The cost is £75.00 per person including VAT
and includes a simple lunch.
(Maximum 5 persons per seminar)
Telephone Heather to book your place on
the next
Merlin Seminar
Tel: 0115 9394122 |
