At present, large-scale outdoor performances in China include professional lighting equipment such as square evenings, large and medium-sized individual concerts, and indoor large and medium-sized stage plays (including studios), such as digital lighting consoles, computer light control, and digital silicon boxes. , computer effect lights, computer color change lights, chasing lights, computer color changers, laser lights, etc., most of them have adopted digital control. How to achieve accurate and correct control of the interconnection between these devices and realize the overall scheduling of the stage lighting is a problem that causes a lot of lighting control. 
Modern stage lighting designers have proposed a new management concept for stage lighting – unified management and centralized control. It is to connect multiple digital lighting devices with different functional effects and control by a digital dimming station. For example, we connect digital dimming silicon boxes, digital color changers, computer effect lights, computer color changing lights, digital hoods, digital bubble machines, etc. to a computer console, controlled by a lighting engineer. Practice has proved to be feasible. This involves the DMX 512 signal transmission system that is well known in the industry.
DMX is an abbreviation for Digital Multipiex. The digital multiplex protocol, defined by the American Theatre Technology Society (USITT), has been recognized and adhered to by the world's production stage equipment manufacturers as a widely adopted digital lighting data protocol; that is, in this link Each controlled unit must comply with the requirements of this agreement in order to achieve centralized control.
DMX is based on RS422/RS485 serial transmission. The data transmission rate is 250Kbit/s and the maximum loop control is 512 channels (of course, there are also 1024\2048 loops, but that is based on 512). Due to the high transmission rate of DMX signal and the special needs of the application environment, DMX signal lines, signal transfer interfaces and signal transmission between various units have strict requirements to ensure the accuracy of signal transmission.
DMX allows an effective transmission distance of 250m. The condition is to use high-quality signal lines, and they should be placed in separate shielding slots during construction; if there is a serious flow or external interference, the length of the signal line should be reduced to shorten the transmission distance. If the engineering requires that the transmission distance of the signal line is greater than 250m, a signal amplifier conforming to the 512 protocol should be installed. Usually a DMX512 interface can drive up to 32 digital devices; if the receiving end uses the DMX487 integrated block to receive signals, then a DMX output interface can drive 128 digital devices.
If a DMX512 system has more than 32 devices, a signal splitter is added, which functions as signal isolation, signal distribution, and signal amplification. A signal distributor has 2~6 output ports (4~8 output ports on the inlet), a signal input port and a loop interface, which can meet the distribution of the lighting system signals of the small and medium stage or studio; If you are in a larger square (such as a stadium), you need to install multiple signal distributors to meet the system needs.
In our stage practice, after adding a signal distributor that conforms to the DMX512 protocol in a multi-unit centralized control link, in addition to amplifying the signal and extending the distance control effect of the cymbal, there is another advantage. : If a lighting device malfunctions (such as leakage, short circuit, etc.), the distributor has photoelectric isolation device, which can effectively protect the lighting equipment in the link.
In the DMX link of a multi-unit unit, the signal interface of the last lighting device should be equipped with a “terminal plug†as impedance matching to eliminate the phenomenon of clutter reflection in signal transmission and purify the signal components. At this time, an important part of the DMX512 system signal transmission is guaranteed. The specific connection method of “terminal plug†is as follows: a small metal film resistor of 90~120Ω 1/4 W is soldered between the 2~3 legs of a five-pin card plug. The impedance should be based on the use of the dimming station. Instructions. Once you're done, plug it into the signal output of the last device. In addition, some digital lighting devices have terminal switches. If such devices are placed at the end of the entire link, the switch should be set to the allowed position, otherwise it should be moved to an invalid position. The DMX protocol requires a five-core plug-in in the link. Only three cores are used in the construction, namely: 1, 2, 3 cores, 4, 5 cores are empty. At present, most imported equipment in the lighting system uses a five-core interface.
In summary, to do a centralized control of large-scale lighting systems requires construction personnel to define the concept and standardize the installation to ensure reliable operation of the system. This will ensure the smooth performance of live lighting effects such as large-scale variety shows and major conferences.
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