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The use and precautions of DMX512

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The use and precautions of DMX512


The purpose of understanding the characteristics of DMX512 signal is to better use it. All the lamps of Reggis can be controlled by DMX512 signal. When using DMX512 control signal, you need to pay attention to the following issues.


(1) DMX512 load: According to the USITT DMX512 protocol standard, each DMX512 output port of the console can control up to 32 "unit loads" connected in series. This "unit load" can be a computer lamp, or a silicon box or other equipment that can accept the DMX512 protocol. Therefore, if you want to control more "unit load" you must use a distributor. Normally, the distributor includes one input port and multiple output ports. In theory, each output port can control 32 "unit loads". However, the number of Chanaels controlled by each DMX512 output port can only be 512, so if you want to control more light paths, you need to have multiple DMX512 output ports. Table 3 lists the relationship between the serial number of the console output port and the number of controlled light paths.


Theoretically, there is no limit to the number of console output ports, but in fact, 4 to 8 DMX512 output ports per console are sufficient.


For example, a console with 6 DMX512 output ports, the number of light paths that can be controlled is: 512x6=3072 (pieces). This means that if it is used to control the dimming cabinet (silicon box), it can control 3072 dimming circuits (Dimmer). If you use it to control scanners, it can control 3072 channels (Chaneel). If the number of channels of a scanner is 20, then the number of scanners controlled by each DMX output port is 25 (512+20=25 more than 12), so the number of scanners that can be controlled by 6 DMX output ports is 150 (6x25=150).


(2) Address code setting problem: Just like each of us has a name, each controlled device must have an address code that can determine its identity. Take the dimming cabinet as an example, each of its loops corresponds to an address code. When the signal command sent by the console is sent to a certain loop, the loop will receive the command and execute it. Of course, this kind of address code needs to be set in advance. For the first DMX output port, maybe we can easily set 1 to 512 address codes, because the big address code is 512. But to set the address code of the subsequent DMX output port, it needs to be calculated carefully. For example, if we want to set the address code of 2331, first determine which output port it belongs to: According to the calculation 2331+512=4 remaining 283 to determine, it belongs to the fifth DMX512 output port. Therefore, when the address of the device needs to be set to the address code of 2331, it is necessary to connect the device to the fifth output port of the console, and the address code is set to 283.



DMX512 signal

DMX512 signal input and output


(3) Precautions in the use of DMX512: The correct use of DMX512 control signals is very important, but for each of our lighting workers, it is often overlooked. Therefore, it is necessary to discuss with you several issues that need to be paid attention to when using DMX512 signals.


①It is very useful to carry a portable DMX512 signal tester at any time. It can check the errors in the system at any time, quickly find the problematic parts, eliminate the faults in time, and ensure the normal operation of the lighting control system.


②The use of qualified signal lines can greatly reduce the trouble in the work. According to the requirements of the DMX512 protocol standard, use twisted-pair shielded cables that meet the specifications to make signal lines, and audio cables must not be used instead. Attention should also be paid to the correct connection of the core wire of the cylindrical plug. In actual work, many faults are caused by broken signal wires, unsoldering of signal wire connectors, and incorrect connection of wire numbers. Therefore, check the continuity of the signal wire and the phase of the core wire before use. , Can achieve the effect of getting twice the result with half the effort.


③When using a three-core DMX512 cylindrical plug, especially when using a five-to-three or three-to-five signal transfer cable, you must pay special attention. Before use, you must carefully understand the equipment's technical requirements for signal phase, and correct the wrong signal connection in time. line.


④Check the ground connection between the controlled device and the DMX512 cylindrical plug. According to the DMX512 standard, the No. 1 core of the cylindrical plug and the No. 1 wire of the controlled device are not allowed to be connected to the shell. Only No. 1 of the console DMX512 output port is allowed. The wire is connected to its chassis. Therefore, after connecting the signal line of the control system, use a tester or a multimeter to check whether there is a shell connection problem on the 1st line. Once it is found, it should be eliminated immediately, otherwise the signal system may be damaged due to accidental electrification of the equipment shell.


⑤When controlling different types of scanners on the same console, because the equipment of each manufacturer will be different, it is easy to cause problems when using mixed installations. Therefore, it is better to install an isolation amplifier between them to connect different types of computers. The lamp is used in isolation. In addition, when renting computer lights or other equipment from other companies, it is also important to install isolation amplifiers between equipment from different companies.


⑥Be careful to separate the power supply of computer lights from the power supply of other electrical equipment (such as silicon boxes and high-power lamps, etc.) in studios or performance venues, otherwise it is very easy to cause damage to the computer due to overload of other electrical equipment. Damage to the lamp.


⑦Keep in mind that a 120Ω terminal resistor should be added to the end of the signal connection line. According to the requirements of the DMX512 signal protocol, a terminal resistor must be connected at the end of each signal chain to form a "closed loop" of the control loop. Therefore, in actual work In, we need to prepare a few more terminal resistors.


⑧Pay attention to the "unit load" problem of the DMX512 system, so that the "unit load" of each output port cannot exceed 32, and add a signal distributor if necessary. In addition, according to our experience, the length of the signal line from the console or distributor to the end controlled device must be less than 200m in order to have a better control effect.


⑨Pay attention to the correct setting of the address code, especially when using scanners, be aware of the channel number of each scanner and the setting method of the address code. Some scanners (such as HIGH END in the United States and SGM in Italy) have their own Special attention should be paid to the special address code setting method.


⑩When laying DMX512 signal cables, try to avoid laying them in parallel with the power cables and light wires at a short distance to reduce the interference of the power supply and the dimming silicon box to the control signal.


In summary, the use of DMX512 signal provides great convenience to the control of stage lighting, and also provides the possibility for the perfect creation of lighting artistic effects. While enjoying the convenience that this technology brings to work, we also need to be more familiar with it, understand its technical characteristics, and know the problems that need to be paid attention to in the process of using it, so as to provide better technical services for the production of TV programs.


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