At present, large outdoor performances, like plaza party, large-sized and medium-sized personal concert theater room (including studio) use professional lighting equipment, such as digital dimming, light control computer, digital silicon case computer effect lights, computers colored lights, track lights change color computer, laser lights, most of which are using a digital control. The interconnection between these devices on how to achieve accurate control and how to achieve the overall scheduling stage lighting is a headache issue.
Modern stage lighting designer for stage lighting presents a new management concept – unified management, centralized control. It means the multi-function digital lighting effects of different devices connected by a digital dimming control. For example, we put digital dimmer boxes, digital color changer, computer effects lights, computers colored lights, digital hood all connected to the digital bubble machine on a computer console to be controlled by a gaffer. Practice has proved that it is feasible. Here it involves the DMX 512 signal transmission system that people are very familiar with.
DMX is the acronym for Digital Multipiex and the translation of digital multiplexing protocol, which is defined by the American Society for Theatre Technology (USITT).It has been recognized and observed by the world’s production and stage equipment manufacturer as the widespread adoption of digital lighting data protocol; That is to say, each controlled unit must comply with the requirements of this agreement in order to achieve centralized control.
DMX RS422/RS485 serial transmission is based on the data transfer at the rate of 250Kbit / s , maximum loop control of which is 512 (of course there are 1024 \ \ 2048 circuit, but that is based on the complex plus 512 made??). Due to the high DMX signal transfer rate and the special needs of application environments, DMX signal transmission signal line and signaling interfaces between the various units have strict requirements to ensure the accuracy of signal transmission. DMX allows the effective transmission distance of 250m on the condition that you should use high-quality signal line and put it in a separate tank shield during construction; when in touring places with serious external interference, you should reduce the length of the corresponding signal lines to shorten the transmission distance. If the project requires the transmission distance to be greater than the signal line 250m, then it should be installed in line with the agreement of the signal amplifier 512. Usually a DMX512 interfaces can drive up to 32 digital devices; If the receiving end in all the manifold is designed to receive DMX487 signal, then a DMX output interface is able to drive 128 digital devices.
If the device with a DMX512 system has more than 32 units, then it is necessary to install a signal splitter to isolate, distribute and amplify signal. A signal splitter has 2 to 6 outputs (4 to 8 output s), a signal input port, a loop interface, which can satisfy the allocation of small and medium stage or studio lighting system signals; In the larger square (like the stadium), it is necessary to install more than one signal distributor to meet system requirements.
In our practice arena, such centralized control in a multi-unit chain in line with the installation of a signal splitter after DMX512 protocol, in addition to the signal amplification to extend the distance manipulation impeach the role, there is a benefit : if a lighting equipment fails (such as leakage, short circuit, etc.), the distributor has optical isolation device ,which can effectively protect the link in the lighting equipment. For DMX link in a multi-device unit, signal interface in the last one lighting equipment should be installed “terminal plug” to eliminate clutter reflection phenomenon in signal transmission and to purify signal components as impedance matching. This is an important part to ensure normal DMX512 signal transmission system. The specific connection method of “Terminal plug ” as follows: welding a 90 ~ 120Ω 1/4 W of small metal film resistors between a five-pin XLR plug 2 to 3 feet , the impedance of which should refer to the size of the instruction manual dimming . After doing that, putting it into the signal output of the last device. There are also some digital lighting equipped with switch terminal itself. If such a device is placed on the end of the entire link, you should switch to appropriate position, or move to an invalid location. DMX protocol requires using the link in the five core plugins. In the construction using only three cores, namely: core 1,2,3, core blank 4, 5. At present, most imported equipment are based on five core lighting system interfaces.