How To Successfully Implement A DMX Installation In 5 Steps
By Stefan Wijdeven
Technical Sales Manager, eldoLED
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The Digital MultipleX (DMX) protocol unlocks an endless possibility of dynamic and fast-changing lighting effects. This is the type of protocol seen in entertainment lighting and is recommended for designers of architectural lighting and other large-scale lighting schemes. Whether it's a rock band's stadium light show or a theatrical stage production, DMX is the key ingredient to maximizing the performance and experience.
Professional lighting designers now leverage DMX-enabled lighting to bring a new emotional dimension to large-scale indoor and outdoor lighting schemes. They need equipment to synchronize sophisticated dimming, switching and color-tuning controls across hundreds of luminaires. This means that the demand for DMX-enabled installations is rising fast—and this gives the lighting equipment supply chain a new incentive to master the technology of DMX.
Restaurant at Sea, Dronten The Netherlands – photo by Peter Baas Photography, courtesy of MoreSenz
Today, most lighting professionals are familiar with the various dimming control DALI protocols—but are less familiar with DMX. DMX offers a greater range of control features than DALI. This includes the independent controlling of 512 fixtures within a single network. Thus, resulting in lighting professionals believing that implementing a DMX network is much more complex and difficult than a DALI Control Scheme.
Contrary to popular belief, it's easy to understand how to operate a DMX network and it only requires attention to a few important rules and guidelines.
As the world's largest supplier of DMX-enabled LED drivers, eldoLED has a unique experience of supporting successful installations in architectural and other professional lighting. We've learned that it's easier to implement a DMX control network than most luminaire manufacturers and installers expect.
Ensure a successful project outcome with our 5 steps on how to implement DMX.
Step 1: Specify the right type of hardware
The main objective of the DMX protocol is guaranteed interoperability between DMX-compatible luminaires, controllers, LED drivers and ballasts from different manufacturers. Any product that's properly tested for conformance with the DMX specifications can work with any other certified DMX component.
This includes any combination of DMX-compatible LED drivers. Our DMX recommendation for luminaire OEMs is the latest POWERdrive family.
These three active components in a DMX network must be DMX-certified:
- Signal Boosters
Cabling 101: RS485 cables are suitable for DMX
It's also crucial to choose the right type of cabling so the installation network successfully operates. DMX signal transmission is identical to RS485 transmission: the high-frequency digital DMX signals are transmitted as a balanced pair of positive and negative mirror images. This is so the interference from high-voltage mains power cabling subtracts when the positive and negative versions of the signal are combined at the receiver (see Figure 1).
Figure 1: the DMX protocol uses shielded twisted pair cable to eliminate the effect of external interference
Like the RS485 signals, DMX signals rely on the use of the shielded twisted-pair cable for interference immunity. This cable may have a marking that shows its compatibility with DMX systems. In general, any cable certified for RS485 networks is also suitable for a DMX network: both the DMX and RS485 cable will have a shielded twisted-pair type.
Using any other cable types for DMX signals will likely result in reliability or performance problems. This interference affects signal integrity and leads to unwanted effects such as visible flicker, unstable operation and slow or failed responses to commands.
Step 2: Specify the right amount of hardware
A DMX network can connect upwards of 512 fixtures to a single controller. Achieve this network capacity by providing each fixture with a unique address. There are 512 available addresses to assign within a single network. All data traffic broadcasts to all nodes—and each node only acts on its addressable part of the data.
The message protocol couples a 0-5V signal to a cable that connects to nodes (luminaires). The cabling's resistance reduces the electrical signal. This means that a single transmitter cannot deliver a strong signal to the entire 512-node network.
0-5V Signal -> Certified DMX Cable -> Nodes/Luminaires
The DMX specifications require signal booster insertions for every 32 fixtures. So, a DMX network containing the maximum number of nodes (512) would require at least 16 signal boosters.
Don't forget the signal boosters
Signal Boosters are often left out of the specification stage due to the cost and the extra installation effort. This is always a mistake. Why? The absence of required signal boosters substantially impairs signal integrity—leading to communications glitches or even complete failure.
At eldoLED, our recommendation is specifying a signal booster for every 25 fixtures. This provides some margin for the unexpected or late addition of fixtures in a section of the network. It also gives the user flexibility that isn't possible for signal boosters per 32 fixtures.
Step 3: Pay attention to the smaller components
The parts of a DMX system that's the most expensive and attracts the most attention from specifiers and installers is the control panel and the luminaires. At eldoLED, we've noticed that most problems arise from a failure to pay attention to two very small and inexpensive components: the termination resistor and surge protection device.
Why termination resistors matter
According to the DMX specifications, a 120Ω termination resistor is required for connection between the positive and negative terminals of the node at the far end of the cable run from the DMX control panel (see Figure 2).
Figure 2: how a termination resistor is connected at the end node of a DMX network
A perfectly specified and installed DMX network can fail due to lacking this simple device—which costs as little as 10 cents. Without it, the network can suffer from distortion and noise caused by signals that reflect back into the network from the farthest node (see Figure 3).
Figure 3: a clean DMX digital signal (left), and the distorted shape of the signal when the absence of a termination resistor causes reflections (right)
Failure to apply a termination resistor will result in faulty performance at the time of installation. Network failure can also occur at any time after the installation is exposed to a damaging surge voltage—which can be caused by a lightning strike.
Why installers matter
Installers are another necessary but often overlooked solution. The installer protects the voltage input line in a DMX system with a surge protection device. The system is only protected if the control line is protected – yet such protection is usually left out of a spec.
You also specify the installer appropriately. While the voltage input line might typically operate at a voltage of 48V, the control line operates at 0-5V—so the same protection device will not be appropriate for both lines.
Step 4: Plan before you install
The electrical and logical rules that encompass a DMX network are straightforward and clear. However, the actual layout is more complex when installing within the structure. This said, you should always make a cabling plan or map before installing the luminaires and cabling. There are two reasons why you should make a plan.
First, it's easier to map the routing for the cable on a map versus the physical space. A routing plan allows the installer to minimize the length—and therefore the cost—of the cabling. It also enables an easy and efficient installation.
Second, you need to keep count of the installed devices number—and then plan for accurate signal boosters insertion. Counting devices pictured on a map is much easier than climbing into a ceiling void or in the tight space underneath floorboards to count the actual devices themselves!
Step 5: Maximize your DMX capabilities
A specifier chooses DMX for architectural and entertainment lighting because of the dynamic and sophisticated effects that it produces—including color tuning and fast transitions.
It makes sense to choose system components that support all the capabilities that DMX has to offer. Even if these capabilities are not all used at the time of installation, the programmability of a DMX system gives the user the freedom to alter the scheme's lighting effects at a later date.
Your DMX system + eldoLED POWERdrive = Endless possibility
When a DMX system uses LED luminaires and eldoLED POWERdrive drivers, the user has guaranteed DMX Features support. Features of the POWERdrive products which support DMX operation in architectural and entertainment lighting include:
- Four (RGB+W) fully programmable, Class-2, constant-current LED outputs supplying up to 1.4A per channel, and up to 3.4A in total, for sophisticated color tuning
- Natural dimming capability, including dim-to-dark, and smooth brightness changes. Flicker-free operation even in broadcast TV environments
- Optically isolated DMX interface to give improved immunity to surge events. Built-in isolation also reduces the risk of damage caused by accidental miswiring
- Each output programmable in 1mA steps via the DMX terminal and eldoLED's proprietary FluxTool software
If you use DALI, you can use DMX
Luminaire manufacturers and lighting installers have become familiar and comfortable with the DALI protocol. On the other hand, DMX's specialized technology is primarily in entertainment lighting. Users elsewhere—such as architectural lighting—have not had as much time to familiarize themselves.
Don't let this deter you from enjoying the full potential that DMX offers. Start creating exciting, evocative and striking lighting displays. The operation of a DMX network follows a clear and limited set of rules. By complying with the five steps above, every manufacturer and installer can be confident of making a success of DMX for their customers.
And of course, the DMX specialists at eldoLED and the guidance on the eldoLED website are always available to give an extra helping hand.
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